@article {5974, title = {Fire and browsing interact to alter intra-clonal stem dynamics of an encroaching shrub in tallgrass prairie}, journal = {Oecologia}, volume = {196}, year = {2021}, pages = {1039 - 1048}, abstract = {

The expansion of woody species into grasslands has altered community structure and ecosystem function of grasslands worldwide. In tallgrass prairie of the Central Great Plains, USA, decreased fire frequency and intensity have increased the cover and abundance of woody species. In particular, clonal shrub cover has increased at accelerated rates due to vegetative reproduction and resprouting after disturbance. We measured the intra-clonal stem demography and relative growth rates (estimated change in woody biomass) of the shrub Cornus drummondii in response to fire frequency (4 vs 20year burn intervals) and simulated browsing during the 2018 and 2019 growing seasons at Konza Prairie Biological Station (Manhattan, Kansas). Overall, infrequent fire (4year burn interval) increased intra-clonal stem relative growth rates and shrub relative growth rates. Intra-clonal stem relative growth rates were reduced in unbrowsed clones in 2018 due to drought and simu-lated browsing reduced intra-clonal stem relative growth rates in 2019. Additionally, simulated browsing nearly eliminated flower production within clones but did not affect intra-clonal stem mortality or recruitment within a growing season. Fire in conjunction with simulated browsing reduced estimated relative growth rates for entire shrub clones. Browsed shrubs that experienced prescribed fire in 2017 had reduced intra-clonal stem densities compared to unbrowsed shrubs and stem densities of browsed shrubs did not recover in 2018 or 2019. These results illustrate that infrequent fire alone promotes the expansion of clonal shrubs in tallgrass prairie and multiple interacting disturbances (e.g., fire and browsing) are required to control the spread of clonal shrubs into grasslands.

}, keywords = {LTER-KNZ}, doi = {10.1007/s00442-021-04980-1}, url = {https://link.springer.com/10.1007/s00442-021-04980-1}, author = {Wedel, E.R. and Nippert, J.B. and D.C. Hartnett} } @article {KNZ001956, title = {The ecology and significance of below-ground bud banks in plants}, journal = {Annals of Botany}, volume = {123}, year = {2019}, pages = {1099 - 1118}, abstract = {

Background
Below-ground bud banks have experienced much recent interest due to discoveries that they (1) account for the majority of seasonal population renewal in many communities, (2) are crucial to regeneration following disturbance, and (3) have important consequences for plant population dynamics and plant and ecosystem function across a number of habitats.

Scope
This review presents an overview of the role of bud banks in plant population renewal, examines bud bank life history, summarizes bud bank traits and their potential ecological implications, synthesizes the response of bud banks to disturbance, and highlights gaps to guide future research. The characteristics and life history of buds, including their natality, dormancy, protection and longevity, provide a useful framework for advancing our understanding of bud banks. The fate of buds depends on their age, size, type, location, and biotic and abiotic factors that collectively regulate bud bank dynamics. A bud bank can provide a demographic storage effect stabilizing population dynamics, and also confer resistance to disturbance and invasion. Regeneration capacity following disturbance is determined by interactions among the rates of bud natality, depletion and dormancy (meristem limitation), and the resources available to support the regeneration process. The resulting response of plants and their bud banks to disturbances such as fire, herbivory and anthropogenic sources determines the community\’s regenerative capacity.

Conclusions
Vegetation responses to environmental change may be mediated through changes in bud bank dynamics and phenology. Environmental change that depletes the bud bank or prohibits its formation likely results in a loss of vegetation resilience and plant species diversity. Standardization of bud sampling, examination of bud banks in more ecosystems and their response to environmental variation and disturbance regimes, employment of stage-structured bud bank modelling and evaluation of the cost of bud bank construction and maintenance will benefit this expanding field of research.

}, keywords = {LTER-KNZ, below-ground organs, Bud, Bud bank, clonal, disturbance, Meristem, Plant traits, population dynamics}, issn = {0305-7364}, doi = {10.1093/aob/mcz051}, url = {https://academic.oup.com/aob/article/123/7/1099/5511692}, author = {Ott, Jacqueline P and Klime{\v s}ov{\'a}, Jitka and D.C. Hartnett} } @mastersthesis {KNZ001957, title = {The ecology of grazing lawns on the tallgrass prairie}, volume = {MS Thesis}, year = {2019}, school = {Kansas State University}, type = {M.S. Thesis}, address = {Manhattan, KS}, keywords = {LTER-KNZ}, url = {https://krex.k-state.edu/dspace/handle/2097/39462}, author = {Shaffer, Monica} } @article {KNZ001836, title = {Bison increase the growth and reproduction of forbs in Tallgrass Prairie}, journal = {American Midland Naturalist}, volume = {178}, year = {2017}, pages = {259}, chapter = {245}, abstract = {

Grazers may increase grassland plant species diversity through mechanisms such as selective consumption of graminoids resulting in release from competition in subordinate forb species, or the enhancement of small-scale habitat heterogeneity. This study tested the hypothesis bison on tallgrass prairie reduce local plant competition and increase the growth, reproduction, abundance, and diversity of forbs. In addition, because grazers, fire, and other drivers result in high spatio-temporal variation in limiting plant resources in tallgrass prairie, we tested the hypothesis that prairie forbs show high phenotypic plasticity in life history traits in response to large grazers.

The growth, reproduction, biomass allocation, and abundances of six common perennial forb species, and estimates of local neighborhood and physical environmental factors were compared in replicate tallgrass prairie sites with and without bison. Greater light availability and percent bare ground; and lower grass canopy density, height, and cover in habitats with bison indicated reduced aboveground plant competition in sites with large grazers. The activities of bison resulted in higher growth and reproduction for all six forb species studied and higher forb species richness. Habitats with bison were also characterized by much higher seed reproduction but no differences in vegetative reproduction compared to habitats without large grazers. Patterns of biomass allocation also showed high plasticity in these species, with reduced allocation to stem and increased allocation to reproduction in habitats with bison. The results of this study provide evidence the activities of bison reduce grass-forb competition, and that release from aboveground competition with grasses increases the growth, seed reproduction, abundance, and ultimately the diversity of perennial forb species in tallgrass prairie. The results further indicate perennial forbs in tallgrass prairie show high phenotypic plasticity in life history traits such as growth, reproduction, and resource allocation patterns.

}, keywords = {LTER-KNZ}, doi = {10.1674/0003-0031-178.2.245}, url = {https://bioone.org/journals/The-American-Midland-Naturalist/volume-178/issue-2/0003-0031-178.2.245/Bison-Increase-the-Growth-and-Reproduction-of-Forbs-in-Tallgrass/10.1674/0003-0031-178.2.245.short}, author = {Elson, A. and D.C. Hartnett} } @article {KNZ001695, title = {Belowground bud bank response to grazing under severe, short-term drought}, journal = {Oecologia}, volume = {178}, year = {2015}, pages = {795-806}, abstract = {

While the effects of drought and grazing are often studied separately, these disturbances co-occur in grasslands worldwide and interactively influence population, community, and ecosystem processes. The effects of drought and grazing on the belowground bud bank may dictate the trajectory of community recovery because new shoots arise from belowground buds after disturbance in perennial grasslands. We therefore investigated the separate and interactive effects of severe drought and grazing on the belowground bud bank and aboveground vegetation in the tallgrass prairie of northeast Kansas, USA. Contrary to our expectations, we observed changes in community structure and declines in species richness both above and below ground in response to drought and grazing. We also hypothesized that drought would reduce bud bank density of all taxonomic groups, but found that grass bud and shoot densities remained constant across all drought and grazing treatment combinations. While sedge and forb bud and shoot densities were reduced by drought, only sedge bud density declined to a greater extent when grazed under drought conditions. Live rhizome biomass did not vary by treatment and was highly correlated with bud bank density, suggesting that bud demography is tightly linked to the production and senescence of rhizomes. Despite the effects of drought and grazing on aboveground net primary productivity and community structure, our work suggests that grasses stabilize tallgrass prairie plant communities because their rhizomes and associated buds persist through co-occurring disturbances.

}, keywords = {LTER-KNZ, Climate change, Ecological stability, Herbivory, tallgrass prairie, water stress}, doi = {10.1007/s00442-015-3249-y}, url = {https://link.springer.com/article/10.1007\%2Fs00442-015-3249-y}, author = {VanderWeide, B.L. and D.C. Hartnett} } @article {KNZ001692, title = {Bud bank dynamics and clonal growth strategy in the rhizomatous grass Pascopyrum smithii}, journal = {Plant Ecology}, volume = {216}, year = {2015}, pages = {395 -405}, abstract = {

Recruitment of rhizomatous perennial grass ramets primarily occurs from the belowground bud bank. Investment in guerilla versus phalanx growth is determined by bud availability, development, and spatial distribution. The tiller and bud bank dynamics of Pascopyrum smithii, a dominant rhizomatous grass of the northern mixed-grass prairie, were examined in South Dakota throughout an annual cycle to assess the investment in guerilla versus phalanx growth and the role of different bud populations in renewal versus regenerative functions and vegetative spread via rhizomes. Pascopyrum smithii invested substantially in both phalanx and guerilla tiller production. However, investment in rhizome production before tiller recruitment prioritized guerilla over phalanx growth. Annual tiller recruitment of P. smithii was capable of flexible timing, occurring in either spring or fall. Renewal buds, from which rhizomes and tillers were recruited, primarily consisted of the youngest generation of buds borne at the base of tillers. Although rhizome axillary buds and older tiller axillary buds were rarely used in annual tiller recruitment, they provided a sizable reserve (regenerative) bud bank. The spatial distribution of bud development produced the mixed guerrilla\–phalanx growth pattern and flexible tiller recruitment timing of P. smithii. Therefore, P. smithii is capable of employing both conservative and foraging growth strategies which will facilitate its persistence under local neighborhood variability and changing resource availability associated with environmental change. Understanding the spatial distribution of buds as determined by rhizome architecture is essential to understanding the distribution and composition of species within plant communities dominated by clonal species.

}, keywords = {LTER-KNZ, Bud, Guerilla, Phalanx Rhizome, Vegetative reproduction, Western wheatgrass}, doi = {10.1007/s11258-014-0444-6}, url = {https://link.springer.com/article/10.1007\%2Fs11258-014-0444-6}, author = {Ott, J.P. and D.C. Hartnett} } @article {KNZ001694, title = {Effects of mycorrhizal symbiosis on aboveground arthropod herbivory in tallgrass prairie: an in situ experiment}, journal = {Plant Ecology}, volume = {216}, year = {2015}, pages = {589 -597}, abstract = {

Plant\–herbivore interactions and mycorrhizal symbiosis are important associations in grasslands that may interact due to their relationships with a common host plant and its resources. However, few studies have explored the effect of mycorrhizal symbiosis on plant\–herbivore interactions. An understanding of the complex interactions between host plants, mycorrhizal fungi, and insect herbivores is enhanced by in situ examinations of the three parties acting simultaneously. The objective of this study was to quantify the effects of mycorrhizal symbiosis on insect herbivory and the host-plant community in tallgrass prairie. We used long-term mycorrhizal and fungicide-treated plots at Konza Prairie Biological Station (Manhattan, KS) to determine whether insect herbivory is altered by suppression of mycorrhizal fungi. Herbivory on plants in mycorrhizal control plots was greater than in fungicide-treated plots, and for one plant guild, C3 graminoids, the difference was significant. In fungicide-treated plots, plant diversity was significantly greater and herbivory was negatively correlated with plant species diversity. Differences in productivity of plant functional groups due to mycorrhizal symbiosis may be a key factor in patterns of insect herbivory. The results indicate that mycorrhizal symbiosis has diverse consequences, influencing the abundance and the quality of host plants in tallgrass prairie, as well as their responses to consumers.

}, keywords = {LTER-KNZ, Arbuscular mycorrhizal fungi, Cool season grass, Forb Mycorrhizal symbiosis, Plant{\textendash}herbivore interactions, Warm-season grass}, doi = {10.1007/s11258-015-0461-0}, url = {https://link.springer.com/article/10.1007\%2Fs11258-015-0461-0}, author = {Kula, A.A.R. and D.C. Hartnett} } @mastersthesis {KNZ001696, title = {Plant responses to grazer-mediated habitat alterations in tallgrass prairie}, volume = {MS Thesis}, year = {2015}, school = {Kansas State University}, type = {M.S. Thesis}, address = {Manhattan, KS}, abstract = {

The effects of bison activities on forb diversity and cover have been well-established, but less is known about how forb life history is altered by bison-mediated habitat changes. This study had three main objectives: 1) to evaluate the hypothesis that release from aboveground competition with grasses may contribute to the increased cover and diversity of forbs in prairie grazed by bison relative to ungrazed prairie, 2) to determine whether differences in forb reproductive effort between grazed and ungrazed habitats were size-dependent, and 3) to look for evidence of a trade-off between allocation to vegetative and sexual reproduction. The growth, biomass allocation, and sexual reproduction of six common unpalatable perennial species were measured and compared between bison-grazed and ungrazed tallgrass prairie burned at 2-year intervals: Ambrosia psilostachya, Artemisia ludoviciana, Baptisia australis, Psoralidium tenuiflorum, Solidago canadensis, and Vernonia baldwinii. Vegetative reproduction was also measured for B. australis\¸ S. canadensis, and V. baldwinii. Light availability, canopy density and height, and percent cover of neighboring plants were measured in each studied individual\’s immediate neighborhood and compared between habitats to establish the possibility of differing aboveground competition. Aboveground competition may be lower in bison-grazed habitats, as evidenced by differences in habitat characteristics and plant performance found in this study. In bison-present habitats, sexual reproduction was elevated for all six species and average plant size was greater for all species except A. psilostachya. Vegetative reproduction was not clearly different between habitats for all three species examined. Sexual reproduction increased with size for all species, and the relationship differed significantly between habitats for all species except A. psilostachya. Allocation to vegetative reproduction was not generally related to aboveground biomass, nor was there a clear trade-off between allocation to vegetative and sexual reproduction. The results of this study provide evidence that release from aboveground competition with grasses promotes the growth and sexual reproduction of the studied species of forb, and that differences in sexual reproduction are not entirely size-dependent. Patterns in allocation to vegetative reproduction were less clear and were not clearly tied to sexual reproductive allocation.

}, keywords = {LTER-KNZ, Competition, forb, Grazing, Life history, Resource allocation, tallgrass prairie}, url = {http://krex.k-state.edu/dspace/handle/2097/19065}, author = {Zahner, A.} } @article {KNZ001693, title = {Vegetative reproduction and bud Bank dynamics of the perennial grass andropogon gerardii in mixed-grass and tallgrass prairie}, journal = {American Midland Naturalist}, volume = {174}, year = {2015}, pages = {14 -34}, abstract = {

Plant species with wide distributions may differ in their population dynamics across their range, especially in contrasting habitats. Most tiller recruitment of perennial grasses occurs vegetatively from the belowground bud bank rather than from seed. Seed reproduction often occurs under a narrower range of environmental conditions than vegetative reproduction. As a result flowering and seedling recruitment patterns of a species often differ between contrasting habitats and across its range. How vegetative reproduction and bud bank dynamics of a species vary between contrasting habitats has not been well studied and could explain the differences in its persistence and productivity between habitats. Therefore, the vegetative reproduction and dynamics of Andropogon gerardii, a dominant C4 perennial grass of the Great Plains of North America, were compared between tallgrass and northern mixedgrass prairie habitats. Bud production and tiller recruitment in 10 populations were examined throughout an annual growing cycle in the northern mixedgrass prairie of South Dakota. Bud bank characteristics, and individual and population performance were compared with previous work conducted in Kansas tallgrass prairie. Stage-structured matrix models examined population growth rates. Andropogon gerardii tillers produced lower numbers of buds and had lower flowering rates in mixedgrass prairie populations. The annual phenology of bud and tiller development was also contracted to fit within the shorter growing season in northern mixedgrass prairie. However, bud longevity and bud bank age structure were similar between habitats, both having buds that lived for \> 2 y and multi-aged bud banks. Similar population growth rates occurred in both habitats despite lower individual performance of both flowering and vegetative reproductive capacity (i.e., bud production) in mixedgrass prairie populations. Lower regional productivity of A. gerardii in northern mixedgrass prairie than in tallgrass prairie does not appear to be due to differences in bud and tiller population growth. Instead, sparse or patchy suitable habitat and/or reduction in tiller size may explain its reduced productivity. Lower population growth rates may be observed in other habitats or in years with harsher environmental conditions that further lower individual performance.

}, keywords = {LTER-KNZ}, doi = {http://dx.doi.org/10.1674/0003-0031-174.1.14}, url = {https://doi.org/10.1674/0003-0031-174.1.14}, author = {Ott, J.P. and D.C. Hartnett} } @article {KNZ001645, title = {Belowground bud banks of tallgrass prairie are insensitive to multi-year, growing-season drought}, journal = {Ecosphere}, volume = {5: art103}, year = {2014}, abstract = {

In tallgrass prairie plant communities, new shoots are recruited from belowground bud banks, often in response to disturbance. We explored the contribution of belowground bud banks to grassland stability when perturbed by severe drought. We sought to quantify changes in bud bank density and demography, assess the contribution of the bud bank to aboveground net primary productivity, and compare shifts in above- and belowground plant community structure in response to drought. We experimentally reduced precipitation 76\% from ambient levels for two years, and compared responses of drought plots to ambient and irrigated controls during the two years of drought and two years of recovery. We measured belowground bud bank density and aboveground shoot density, canopy cover, and aboveground net primary productivity. While aboveground net primary productivity and C4 grass flowering shoot density declined during drought, bud bank density was insensitive to drought. Rapid resilience of the aboveground plant community following cessation of drought appears to be mediated by the resistance of bud banks to drought. Shoot density, but not bud bank density, was positively correlated with total aboveground net primary productivity. Furthermore, proportional reductions in aboveground net primary productivity increased as shoot density increased. Plant community structure shifted both above- and belowground in response to precipitation treatments. Our results suggest that the response of perennial grasslands to drought may be mediated by the stable belowground bud bank, with shifts in abundance of individual species maintaining overall bud bank density and ecosystem function.

}, keywords = {LTER-KNZ}, doi = {10.1890/ES14-00058.1}, url = {https://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/ES14-00058.1}, author = {VanderWeide, B.L. and D.C. Hartnett and Carter, D.L.} } @phdthesis {KNZ001650, title = {Ecological implications of grass bud bank and tiller dynamics in mixed-grass prairie}, volume = {PhD. Dissertation}, year = {2014}, school = {Kansas State University}, type = {Ph.D. Thesis}, address = {Manhattan, KS}, abstract = {

Perennial grass populations propagate vegetatively via the belowground bud bank. Climate, photosynthetic pathway, and growth form impact bud production, longevity, and dormancy; leading to alterations in bud bank and tiller dynamics. Previous research in mesic C$_{4}$-dominated tallgrass prairie revealed that a C$_{4}$ grass had greater bud longevity and differing bud bank dynamics than a C$_{3}$ species. This study examined the bud bank dynamics of rhizomatous and caespitose grasses in a more arid C$_{3}$ dominated prairie to gain insights into how bud banks differ among grass species, growth forms, and environments, and the relationship between bud bank characteristics and grass architecture and growth patterns. The bud bank and tiller dynamics of four perennial grasses in the C$_{3}$-dominated northern mixed grass prairie were examined over 15 months. The C$_{3}$ caespitose and rhizomatous grasses produced similar numbers of buds per tiller and their bud longevity was [greater than or equal to] 2 years. Tiller longevity drove the turnover within the bud bank of the dominant C$_{3}$ caespitose grasses Hesperostipa comata and Nassella viridula. Their polycyclic tillers (tillers that lived for more than one year) created multi-aged bud banks. The rhizomatous C$_{3}$ grass Pascopyrum smithii also had a multi-aged bud bank because buds were able to live longer than its annual tillers. Differences between caespitose and rhizomatous C$_{3}$ grass bud banks were driven by differences in tiller and rhizome production and spatial distribution. Responses to water availability fluctuations are likely buffered by the maintenance of polycyclic tillers in the caespitose grasses and flexible timing of annual tiller recruitment in the rhizomatous grass. The C$_{4}$ rhizomatous grass Andropogon gerardii had similar phenology to populations in its tallgrass prairie range center. Despite declines in bud production per tiller and lowered flowering probability in mixed-grass prairie, A. gerardii maintained a multi-aged bud bank and a positive population growth rate via vegetative reproduction at both the center and edge of its range. Bud bank dynamics of different growth forms and photosynthetic pathways, as they offer insight into the control of grass population dynamics and production, will enhance understanding of the mechanisms by which management practices and environmental change can alter perennial grasslands.

}, keywords = {LTER-KNZ, Bud bank, Grass; Mixed-grass prairie, perennial grass, Tiller dynamics, Vegetative reproduction}, url = {http://hdl.handle.net/2097/17277}, author = {Ott, J.P.} } @phdthesis {KNZ001571, title = {Grazing and drought in tallgrass prairie: the role of belowground bud banks in vegetation dynamics}, volume = {PhD. Dissertation}, year = {2013}, school = {Kansas State University}, type = {Ph.D. Thesis}, address = {Manhattan, KS}, abstract = {

Grazing and drought are instrumental in the development and maintenance of perennial grasslands. In this research I tested the belowground bud bank contribution to tallgrass prairie resistance and resilience when perturbed by grazing and drought. First, I tested the bud bank role in vegetation response to and recovery from severe drought (Chapter 2). I compared above- and belowground responses of experimentally droughted plots to ambient controls and irrigated plots during two years of severe drought and two years of recovery. I found that although aboveground net primary productivity declined 30-60\% during drought, bud bank density and demography were insensitive to drought. These results suggest that grassland resistance and resilience when perturbed by drought may be mediated by stability of belowground bud banks. Second, I investigated vegetation and soil nutrient legacies following release from long-term grazing (Chapter 3). I documented a relatively rapid shift in aboveground vegetation within four years of grazer exclusion, with productivity, stem density, and diversity becoming relatively more similar to ungrazed than grazed prairie. The density and composition of the belowground bud bank and soil seed bank shifted more slowly, remaining more similar to grazed than ungrazed prairie. Responses of soil nutrients to removal of grazers varied, and in some cases was affected by recent fire history. These results demonstrate the contribution of belowground propagules to the maintenance of a diverse plant community both during grazing and after grazers are removed. Finally, I examined short-term vegetation responses to both drought and grazing (Chapter 4). Despite extreme drought and simulated grazing that reduced productivity and increased mortality of individual stems, the dominant C4 grasses maintained a stable bud bank. Aboveground net primary productivity and bud bank density of sedges and forbs, however, were reduced by both drought and grazing. This differential response of species to extreme drought and grazing led to shifts in community composition and species diversity over one growing season. Across drought and grazing treatments, live rhizome biomass was highly correlated with bud bank density and may be a useful, more easily measured index of bud bank density.

}, keywords = {LTER-KNZ, Bud bank, Grazing; Drought, Resistance and resilience, Seed bank, tallgrass prairie}, url = {http://hdl.handle.net/2097/16622}, author = {VanderWeide, B.L.} } @article {KNZ001548, title = {Variation in root system traits among African semi-arid savanna grasses: implications for drought tolerance}, journal = {Austral Ecology}, volume = {38}, year = {2013}, pages = {383 -392}, abstract = {

In arid to semi-arid grasslands and savannas, plant growth, population dynamics, and productivity are consistently and strongly limited by soil water and nutrient availability. Adaptive traits of the root systems of grasses in these ecosystems are crucial to their ability to cope with strong water and/or nutrient limitation and the increasing drought stress associated with ecosystem degradation or projected climate change. We studied 18 grass species in semi-arid savanna of the Kalahari region of Botswana to quantify interspecific variation in three important root system traits including root system architecture, rhizosheath thickness and mycorrhizal colonization. Drought-tolerant species and shorter-lived species showed greater rhizosheath thickness and fine root development but lower mycorrhizal colonization compared to later successional climax grasses and those characteristic of wetter sites. In addition, there was a significant positive correlation between root fibrousness index and rhizosheath thickness among species and a weak negative correlation between root fibrousness index and mycorrhizal colonization. These patterns suggest that an extensive fine root system and rhizosheath development may be important complementary traits of grasses coping with drought conditions, the former aiding in the acquisition of water by the grass plant and the latter aiding in water uptake and retention, and reducing water loss in the rhizosphere. Within species, both rhizosheath development and mycorrhizal colonization were significantly greater in a wet year than in a year with below-average precipitation. The observed patterns suggest that the primary benefit of rhizosheath development in African savanna grasses is improved drought tolerance and that it is a plastic trait that can be adjusted annually to changing environmental conditions. The functioning of mycorrhizal symbiosis is likely to be relatively more important in infertile savannas where nutrient limitation is higher relative to water limitation.

}, keywords = {LTER-KNZ, grass, mycorrhiza, rhizosheath, root architecture, savanna}, doi = {10.1111/j.1442-9993.2012.02422.x}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1442-9993.2012.02422.x}, author = {D.C. Hartnett and Ott, J.P. and G.T. Wilson and Setshogo, M.} } @article {KNZ001492, title = {Contrasting bud bank dynamics of two co-occurring grasses in tallgrass prairie: implications for grassland dynamics}, journal = {Plant Ecology}, volume = {213}, year = {2012}, pages = {1437 -1448}, abstract = {

Because most shoot recruitment in perennial grasses occurs from belowground axillary buds, bud dynamics determine plant population dynamics and meristem limitation to population growth. Therefore, grassland vegetation responses to environmental change or disturbance may be influenced by interspecific differences in bud banks and the patterns and environmental controls of bud development and demography. We examined bud bank dynamics in Andropogon gerardii and Dichanthelium oligosanthes in tallgrass prairie by enumerating and classifying buds throughout 15 months to determine whether grass buds live for multiple years and accumulate; whether bud natality, dormancy and outgrowth are synchronous or variable; and whether bud bank dynamics differ between these co-occurring species. Andropogon gerardii (a C4 species) maintained a larger dormant bud bank, showed synchrony in bud development and transition to tiller, and its buds lived for multiple years. Thus, multiple previous years\’ bud cohorts contributed to recruitment. By contrast, D. oligosanthes (a C3 species) maintained a smaller dormant bud bank, had asynchronous bud development with active buds present year-round, and its buds lived for 1 year. Buds played different roles in the dynamics of each species, allowing A. gerardii to over-winter and recruit new spring tillers and D. oligosanthes to survive and recruit new tillers following summer dormancy. These differences in bud bank age structure, phenology, and dynamics between these species suggest greater demographic buffering and time-lag effects in A. gerardii populations. Interspecific differences in bud bank structure and dynamics may explain and help predict grassland responses to environmental change.

}, keywords = {LTER-KNZ, Meristem, Photosynthetic pathway, Plant demography, Plant population dynamics, Tiller recruitment, Vegetative reproduction}, doi = {10.1007/s11258-012-0102-9}, url = {https://link.springer.com/article/10.1007\%2Fs11258-012-0102-9}, author = {Ott, J.P. and D.C. Hartnett} } @article {KNZ001551, title = {Controls on bud activation and tiller initiation in C3 and C4 tallgrass prairie grasses: the role of light and nitrogen}, journal = {Botany}, volume = {90}, year = {2012}, pages = {1221 -1228}, abstract = {

Population dynamics of perennial grasses in tallgrass prairie ecosystems are strongly influenced by vegetative outgrowth from their belowground bud banks. We examined the role of light and nitrogen in regulating tiller initiation and tested an integrated model of controls on bud dormancy and activation in several C3 and C4 grasses. In addition, we assessed the interaction of nitrogen and light quantity and red \– far red spectral composition on tiller initiation. Belowground perennating organs of three C3 and three C4 species were grown under full light or dark conditions, amended with one of four nitrogen concentrations (0 to 350 ppm N). Dormant buds were also subjected to full light under different spectral compositions or to continuous darkness. Our results among C3 grasses support the integrated model as light and nitrogen played important and interacting roles in the regulation of bud banks. However, differences in responses among C4 grasses and a lack of light \× nitrogen interactions suggest that an alternative model may be necessary for this functional group. Our results provide predictions of responses to nitrogen enrichment or light imitations in prairie ecosystems due to interacting disturbances such as reduction in fire frequencies, alterations in grazing intensities, or climate change.

}, keywords = {LTER-KNZ, bud banks, C3 grasses, C4 grasses, perennial grasses, Tiller recruitment, Vegetative reproduction}, doi = {10.1139/b2012-091}, url = {http://www.nrcresearchpress.com/doi/10.1139/b2012-091}, author = {Williamson, M. and G.T. Wilson and D.C. Hartnett} } @article {KNZ001549, title = {Coping with herbivory at the juvenile stage: Responses to defoliation and browsing in the African savanna tree Colophospermum mopane}, journal = {Journal of Tropical Ecology}, volume = {28}, year = {2012}, pages = {161 -169}, abstract = {

Responses of plants to herbivory are dependent on the type of damage and the ontogenetic stage of the plant. We compared the effects of stem pruning and defoliation on seedlings of Colophospermum mopane, an ecologically important tree species widely distributed in southern Africa. The growth of 160 greenhouse-grown juveniles were measured for 6-mo after germination and then 6-mo after treatments including 50\% defoliation, 100\% defoliation, 50\% stem pruning and controls. Pruning resulted in 30\% reductions in total leaf area, height and biomass. Partial defoliation resulted in 30\% reductions in total leaf area and plant biomass. However, complete defoliation resulted in a 30\% increase in biomass production, a doubling in leaf and lateral branch number, a 45\% reduction in leaf size, and no change in total leaf area. Thus, completely defoliated seedlings showed greater performance than those that were only partially defoliated, indicating that C. mopane has become adapted to the chronic and severe defoliation inflicted by Imbrasia belina caterpillars. Comparison of our results with other studies indicates that C. mopane seedlings are less herbivory-tolerant than adults and that pruning has more negative effects than defoliation. Thus, seedling browsers may constrain recruitment in C. mopane, influencing its population dynamics and abundance.

}, keywords = {LTER-KNZ, Botswana, browsing, defoliation, Herbivory, Plant{\textendash}herbivore interactions, savanna, seedlings, tree recruitment}, doi = {http://dx.doi.org/10.1017/S0266467412000028 }, url = {https://www.cambridge.org/core/journals/journal-of-tropical-ecology/article/coping-with-herbivory-at-the-juvenile-stage-responses-to-defoliation-and-stem-browsing-in-the-african-savanna-tree-colophospermum-mopane/5B519E0F1B9BD889D4905FD311257D9A}, author = {D.C. Hartnett and Ott, J.P. and Sebes, K. and Ditlhogo, M.} } @article {KNZ001486, title = {Higher-order bud production increases tillering capacity in the perennial caespitose grass Scribner{\textquoteright}s Panicum (Dichanthelium oligosanthes)}, journal = {Botany}, volume = {90}, year = {2012}, pages = {884 -890}, abstract = {

The persistence and dynamics of perennial grass populations strongly depend on tiller recruitment from the bud bank. Because of the structural organization of grasses as populations of phytomers, bud production and tillering are constrained by morphology. An infrequent trait observed in only a few caespitose grasses is the branching of buds to produce higher-order buds prior to tiller development. We studied bud bank dynamics in Dichanthelium oligosanthes (Schult.) Gould a C3 perennial caespitose grass widely distributed in the eastern Great Plains. A hierarchy of bud development occurred in D. oligosanthes, with primary buds branching to produce secondary, tertiary, and quaternary buds. This higher-order bud production increased the overwintering propagule supply for spring recruitment by 4.5 times, and more than half of successful tiller recruits originated as higher-order buds. The temporal patterns of higher-order bud production and development suggest that growing season length may be an important factor determining the extent of higher-order bud production and subsequent year tiller natality in D. oligosanthes. Higher-order bud production likely has important consequences for the population dynamics of grasses. It may increase bud bank densities and tillering capacity, buffer population dynamics, and increase intraclonal tiller densities and resource consolidation in caespitose grasses.

}, keywords = {LTER-KNZ, Bud bank, bunchgrass, Dichanthelium oligosanthes, tillering}, doi = {10.1139/b2012-043}, url = {http://www.nrcresearchpress.com/doi/10.1139/b2012-043}, author = {Ott, J.P. and D.C. Hartnett} } @article {KNZ001550, title = {Interspecific variation in bud banks and flowering effort among semi-arid African savanna grasses}, journal = {South African Journal of Botany}, volume = {83}, year = {2012}, pages = {127 -133}, abstract = {

Population viability and productivity of grasses in southern African savannas are dependent upon both successful seed production and tiller recruitment from the belowground bud bank. Relative recruitment rates from buds versus seeds influence population dynamics, genetic diversity, and patterns of vegetation productivity. We assessed patterns in bud bank size and flowering effort in fourteen semi-arid savanna grass species in the Kalahari region of Botswana. There was high inter-specific variability and between-year variability in flowering effort (percentage of tillers flowering). Bud production (number of buds per tiller) exhibited high inter-specific variability, but was more consistent between-years than flowering effort. Relative allocation to flowering versus bud production varied with life history, with longer-lived perennial grasses showing higher bud production and lower flowering effort relative to shorter-lived grasses. Several species showed higher bud production and lower flowering effort in a wet year compared to a dry year, and grass species that are regularly grazed maintained significantly larger bud banks than non-grazed species. These differential demographic responses among co-occurring species suggest that environmental change in semi-arid savannas may alter the composition, relative abundances and diversity of grasses, and that the maintenance of a belowground bud bank is an important factor influencing their resiliency, their capacity to recover from grazing and/or drought, and their persistence and sustainability under changing environmental conditions. Meristem-limitation in species that maintain few viable buds may constrain their population viability under changing conditions in semi-arid savannas.

}, keywords = {LTER-KNZ, Bud bank, Meristem, Poaceae, Reproductive allocation, Vegetative reproduction}, doi = {10.1016/j.sajb.2012.08.010}, url = {https://www.sciencedirect.com/science/article/pii/S0254629912001275?via\%3Dihub}, author = {Dalgleish, H.J. and Ott, J.P. and Setshogo, M. and Muzilla, M. and D.C. Hartnett} } @article {KNZ001415, title = {Bud production and dynamics of flowering and vegetative tillers of the perennial grass Andropogon gerardii (Poaceae): the role of developmental constraints}, journal = {American Journal of Botany}, volume = {98}, year = {2011}, pages = {1293 -1298}, abstract = {

\•Premise of the Study: Perennial grasses maintain aboveground tiller populations through vegetative reproduction via belowground buds and sexual reproduction via seed. The maintenance of a bud bank has important demographic consequences for perennial grasses. A tradeoff between these reproductive modes would be expected for a plant with limited resource availability. However, the ontogeny of the tiller could affect its ability to allocate between these two modes of reproduction. \•Methods: Vegetative bud production and dynamics and tiller production were examined biweekly through an annual cycle on vegetative and flowering tillers of Andropogon gerardii. \•Key Results: Andropogon gerardii maintains a large reserve of dormant buds. Although vegetative and flowering tillers had similar bud phenology, flowering tillers produced larger numbers of buds of larger size, and transitioned a larger proportion of their buds to tiller, than did vegetative tillers. Therefore, a negative consequence of sexual reproduction on vegetative reproduction was not evident at the tiller level. A size threshold for floral induction likely exists that results in flowering tillers having more buds per tiller than vegetative tillers. The increased bud outgrowth of flowering tillers could be a result of their larger bud size or weaker apical dominance as compared to vegetative tillers. \•Conclusions: Plant development can place significant constraints on tradeoffs between the reproductive modes in perennial grasses and could affect their plasticity in plant reproductive allocation. Differences in developmental phenology and bud production between flowering and vegetative tillers may influence grass responses to environmental changes such as altered precipitation regimes or resource availability.

}, keywords = {LTER-KNZ, allocation, axillary bud, Bud bank, Meristem, ontogeny, perennial grass, Tiller recruitment, tradeoff, Vegetative reproduction}, doi = {10.3732/ajb.1000264}, url = {https://bsapubs.onlinelibrary.wiley.com/doi/full/10.3732/ajb.1000264}, author = {Ott, J.P. and D.C. Hartnett} } @article {KNZ001363, title = {Differential responses to defoliation frequency in Little Bluestem (Schizachyrium scoparium) in tallgrass prairie: Implications for herbivory tolerance and avoidance}, journal = {Plant Ecology}, volume = {212}, year = {2011}, pages = {1275 -1285}, abstract = {

Plant responses to herbivory are complex. In grasses, relative growth rate (RGR), seed, and vegetative reproduction, resource allocation, and architecture vary differentially and often nonlinearly with grazing intensity. High grazing tolerance may be achieved through compensatory photosynthesis and leaf growth, or through demographic mechanisms such as activation of a belowground dormant bud bank. This study assessed the relationship between grazing frequency and responses of Schizachyrium scoparium (little bluestem) in a tallgrass prairie, and examined the roles of tiller growth, reproduction, and bud (meristem) populations in its persistence under grazing. Genets were subjected to varying simulated grazing frequencies for a period of 2 years. Strong differential responses were observed among plant traits. RGR, biomass, and flowering showed strong nonlinear reductions in response to increasing clipping frequency, with no evidence of threshold effects. However, meristem density was unaffected, and plants maintained a large bud bank across all clipping treatments. Tiller natality decreased initially, but increased with \>4 clippings, suggesting that declines in tiller RGR are partially offset by increasing tiller natality, and that variation in genet size is driven more by demography than by variation in individual tiller growth. Increased grazing frequency also resulted in differential activation of buds at different positions (emerging within vs. outside the subtending leaf sheath), explaining the shift to a more prostrate growth form observed in many caespitose grasses under persistent grazing. Thus, although this grass species lacks the capacity for compensatory foliage re-growth, the maintenance of a large dormant bud bank and the differential activation of buds in different positions contribute to its grazing tolerance and avoidance, respectively, and its long-term persistence in grazed grasslands.

}, keywords = {LTER-KNZ, bud banks, Compensation, demography, Grasses, Grazing, Herbivory}, doi = {10.1007/s11258-011-9904-4}, url = {https://link.springer.com/article/10.1007\%2Fs11258-011-9904-4}, author = {N{\textquoteright}Guessan, M. and D.C. Hartnett} } @article {KNZ001414, title = {Fire resistance of tree species explains gallery forest community composition}, journal = {Forest Ecology and Management}, volume = {261}, year = {2011}, pages = {1530 -1538}, abstract = {

Fire, climatic variability, and grazing by large herbivores have historically limited woody vegetation in the tallgrass prairie region of North America to gallery forests in protected areas along rivers and streams. Fire, in particular, has been a strong selective pressure against woody vegetation. Consequently, we expect that dominant tree species in these forests have developed mechanisms for tolerating periodic surface fires. Susceptibility of trees to fire damage depends in part on key properties of bark which influence heat transfer to the vascular cambium, including thickness, density, and moisture content. An historical (1983) survey of Konza Prairie Biological Station in northeast Kansas, USA indicated that gallery forests were co-dominated by Quercus macrocarpa and Quercus muehlenbergii, while Celtis occidentalis occurred as an important sub-dominant species. Populus deltoides, Gleditsia triacanthos, and Juniperus virginiana were relatively uncommon. To test the hypothesis that historically dominant gallery forest tree species are more resistant to fire damage than uncommon species, fire was applied to the bark of 10 individuals of each of these six species under conditions mimicking surface fires (400 \°C for 120 s). Maximum temperature at the vascular cambium, bark thickness, bark moisture content, and bark density were measured. Trees were considered fire-resistant if the vascular cambium temperature remained below the thermal cell death threshold, 60 \°C, throughout the treatment. Using logistic regression, bark thickness was found to be a significant predictor of lethal cambium temperatures (P = 0.002), while neither bark density nor moisture content were significantly related to lethal cambium temperature (P = 0.279 and P = 0.131, respectively). Across species, a minimum bark thickness of approximately 8.6 mm was necessary to maintain the vascular cambium temperature below 60 \°C. Trees that produce thick bark quickly in juvenile size classes (P. deltoides, Q. macrocarpa, and Q. muehlenbergii) experienced lower temperatures at the vascular cambium than those which do not develop thick bark with increasing diameter (C. occidentalis, G. triacanthos, and J. virginiana). Ranking these tree species by either the DBH or age needed to develop the minimum protective bark thickness largely agreed with ranking based on historical relative importance. As fire frequency and intensity decrease in remnant tallgrass prairie of North America as a result of habitat fragmentation, fire suppression, and changing land management, fire-sensitive species may increase in relative importance in gallery forests because of increased juvenile survival.

}, keywords = {LTER-KNZ, Bark, Fire resistance, Forest composition, gallery forest, Konza Prairie}, doi = {10.1016/j.foreco.2011.01.044}, url = {https://www.sciencedirect.com/science/article/pii/S0378112711000764?via\%3Dihub}, author = {Vanderweide, B. and D.C. Hartnett} } @article {KNZ001362, title = {Rhus glabra response to season and intensity of fire in tallgrass prairie}, journal = {International Journal of Wildland Fire}, volume = {20}, year = {2011}, pages = {709 -720}, abstract = {

Altered fire regimes play a key role in shrub expansion in grasslands worldwide. We assessed how season and type or intensity of fire affected the growth and demography of Rhus glabra, a common woody invader in North American mesic grasslands. Fire during any season killed 99\% of ramets but stimulated new ramet recruitment from belowground buds, resulting in a near-complete turnover of ramet populations. During the first 2 years following fire, populations on spring-burned sites had the greatest post-fire ramet densities and population growth rates, and winter- and spring-burned populations showed the highest resprouting rates. However, after 10 years, R. glabra cover on summer-burned sites was 3.5 times greater than on autumn- or winter-burned treatments. Thus, short-term post-fire responses may not be good predictors of long-term changes in abundance. Low-intensity spring backfires resulted in the highest ramet population growth rates, whereas high-intensity headfires in any season resulted in slower growth, and populations burned with low-intensity winter fires declined. In addition, season of fire influenced browsing pressure, suggesting that plant responses may be partially a result of indirect effects of fire on rates of herbivory. Overall, our results demonstrate that the application of frequent autumn or winter backfires is an effective management tool for limiting R. glabra expansion in grasslands, and that long-term data are critical for management decision-making, particularly in systems characterised by high interannual climate variability.

}, keywords = {LTER-KNZ, shrub demography, shrub encroachment, smooth sumac}, doi = {10.1071/WF09127}, url = {http://www.publish.csiro.au/wf/WF09127}, author = {K.M. Hajny and D.C. Hartnett and G.T. Wilson} } @mastersthesis {KNZ001394, title = {Controls on bud activation and tiller initiation in tallgrass prairie: The effect of light and nitrogen}, volume = {MS Thesis}, year = {2010}, pages = {1 -52}, school = {Oklahoma State University}, type = {M.S. Thesis}, address = {Stillwater, OK}, abstract = {

Chapter 1: Perennial grass populations in tallgrass prairie ecosystems are maintained primarily through vegetative outgrowth from their belowground bud banks. Resources in these ecosystems that have been found to limit plant productivity include nitrogen and light. I tested the Tomlinson and O\&$\#$39;Connor (2004) theory, on the interactions of two environmental cues, nitrogen and light quantity, and the roles they have on bud outgrowth and tiller initiation in six perennial grass species in two functional groups (C 3 and C 4 photosynthetic pathways). I hypothesized that (1) an interaction between nitrogen and light availability regulated bud activation and tiller emergence in the two functional groups (C 3 species and C 4 species), (2) nitrogen would have the largest effect on the activation of buds, and (3) responses to the two environmental cues would differ between the two functional groups. Environmental growth chambers were used to conduct all studies, plants received one of three NH 4 NO 3 amendments or water (control), and were placed in a light treatment chamber or a dark (control) chamber. Strong interactions between nitrogen and light influenced bud outgrowth in the C c species, but not in the C 4 species. When I assessed the impacts of nitrogen as a key cue in tiller initiation in all six species, C 3 species responded favorably to N, while C 4 species did not. These results indicate that another abiotic environmental cue may be influencing the C 4 species. The results of this study suggest that environmental cues such as these that impact belowground bud bank dynamics in the tallgrass prairie have to potential to significantly impact grassland dynamics in response to current and future global changes. Chapter 2: Three species of C 3 grasses and three species of C 4 grasses were studied to test a proposed theory (Tomlinson and O\&$\#$39;Connor 2004), to determine the role that light spectral quality (R:FR) and light quantity have on belowground bud outgrowth. I hypothesized that (1) R:FR will be an important cue in the regulation of bud bank dynamics, (2) reductions in light quantity due to litter accumulation will significantly reduce bud outgrowth, and (3) the response to the two factors will not be consistent across the two functional groups. Environmental growth chambers were used to conduct all study treatments. Plants were placed in chambers under one of three light treatments: light, reduced R:FR, or a full dark (control). To assess the effects of light availability under natural conditions, litter was used to reduce light availability in the C 4 species. Light spectral quality and quantity elicited species-specific responses in both of the functional groups. A suppression in bud outgrowth in response to R:FR reductions were observed in four of the six species. Alterations to light quantity due to litter accumulation did not reduce bud outgrowth, but a reduction in R:FR did, suggesting that light spectral quality is a more important regulator of bud dormancy and outgrowth than light intensity. Surprisingly, the response to light spectral quality and quantity were consistent across both functional groups. As we continue to seek answers to enhance rangeland quality, assessing how environmental cues are interacting may be a stronger predictor of how rangelands will respond to current and future global changes, than assessing the cues individually.

}, keywords = {LTER-KNZ}, url = {http://hdl.handle.net/11244/9577}, author = {Williamson, M.M.} } @article {KNZ001344, title = {Into Africa: Promoting international ecological research and training in the developing world}, journal = {Bulletin of the Ecological Society of America}, volume = {91}, year = {2010}, pages = {202 -206}, keywords = {LTER-KNZ}, doi = {10.1890/0012-9623-91.2.202}, author = {D.C. Hartnett} } @article {KNZ001317, title = {The effects of fire frequency and grazing on tallgrass prairie productivity and plant composition are mediated through bud bank demography}, journal = {Plant Ecology}, volume = {201}, year = {2009}, pages = {411 -420}, abstract = {

Periodic fire, grazing, and a variable climate are considered the most important drivers of tallgrass prairie ecosystems, having large impacts on the component species and on ecosystem structure and function. We used long-term experiments at Konza Prairie Biological Station to explore the underlying demographic mechanisms responsible for tallgrass prairie responses to two key ecological drivers: fire and grazing. Our data indicate that belowground bud banks (populations of meristems associated with rhizomes or other perennating organs) mediate tallgrass prairie plant response. Fire and grazing altered rates of belowground bud natality, tiller emergence from the bud bank, and both short-term (fire cycle) and long-term (\>15 year) changes in bud bank density. Annual burning increased grass bud banks by 25\% and decreased forb bud banks by 125\% compared to burning every 4 years. Grazing increased the rate of emergence from the grass bud bank resulting in increased grass stem densities while decreasing grass bud banks compared to ungrazed prairie. By contrast, grazing increased both bud and stem density of forbs in annually burned prairie but grazing had no effect on forb bud or stem density in the 4-year burn frequency treatment. Lastly, the size of the reserve grass bud bank is an excellent predictor of long-term ANPP in tallgrass prairie and also of short-term interannual variation in ANPP associated with fire cycles, supporting our hypothesis that ANPP is strongly regulated by belowground demographic processes. Meristem limitation due to management practices such as different fire frequencies or grazing regimes may constrain tallgrass prairie responses to interannual changes in resource availability. An important consequence is that grasslands with a large bud bank may be the most responsive to future climatic change or other global change phenomena such as nutrient enrichment, and may be most resistant to exotic species invasions.

}, keywords = {LTER-KNZ, Bud bank, fire, Grazing, Konza Prairie LTER, Meristem, Vegetative reproduction}, doi = {10.1007/s11258-008-9562-3}, url = {https://link.springer.com/article/10.1007\%2Fs11258-008-9562-3}, author = {Dalgleish, H.J. and D.C. Hartnett} } @article {KNZ001286, title = {High propagule production and reproductive fitness homeostasis contribute to the invasiveness of Lespedeza cuneata (Fabaceae)}, journal = {Biological Invasions}, volume = {11}, year = {2009}, pages = {1913 -1927}, abstract = {

Comparative studies of congeneric native and exotic species have proved fruitful in understanding plant traits that foster invasion. Using this approach, we investigate the complex reproductive system of the invasive Lespedeza cuneata (Dum.-Cours.) G. Don in relation to three native congeners in the variable environment of the North American tallgrass prairie. Lespedeza species produce both chasmogamous (CH) and cleistogamous (CL) flowers, and propagate clonally via vegetative buds. Utilizing multiple natural populations over 2 years, we investigated reproductive modes of individuals from bagged and unbagged treatments of each species. We found that L. cuneata produced a mean of five times as many seeds and a significantly greater number of vegetative buds than any native studied, and over twenty times as many CH flowers. Insect visitation significantly affected seed set in CH flowers, though some autonomous CH selfing occurred in all species. The invasive relied relatively less on selfing than the natives and exhibited less variation in reproductive output from both modes of reproduction. We conclude that the diverse reproductive biology and wide regeneration niche of L. cuneata in relation to its native congeners confer a fitness homeostasis that facilitates the successful spread of this invasive under a wide range of conditions.

}, keywords = {LTER-KNZ, Cleistogamy, Fitness homeostasis, Invasive, Lespedeza, Pollination, Propagule production, Regeneration niche, tallgrass prairie}, doi = {10.1007/s10530-008-9369-0}, url = {https://link.springer.com/article/10.1007\%2Fs10530-008-9369-0}, author = {Woods, T.M. and D.C. Hartnett and Ferguson, C.J.} } @article {KNZ001248, title = {Soil aggregation and carbon sequestration are tightly correlated with the abundance of arbuscular mycorrhizal fungi: results from long-term field experiments}, journal = {Ecology Letters}, volume = {12}, year = {2009}, pages = {452 -461}, abstract = {

We examined the role of arbuscular mycorrhizal fungi (AMF) in ecosystems using soil aggregate stability and C and N storage as representative ecosystem processes. We utilized a wide gradient in AMF abundance, obtained through long-term (17 and 6 years) large-scale field manipulations. Burning and N-fertilization increased soil AMF hyphae, glomalin-related soil protein (GRSP) pools and water-stable macroaggregates while fungicide applications reduced AMF hyphae, GRSP and water-stable macroaggregates. We found that AMF abundance was a surprisingly dominant factor explaining the vast majority of variability in soil aggregation. This experimental field study, involving long-term diverse management practices of native multispecies prairie communities, invariably showed a close positive correlation between AMF hyphal abundance and soil aggregation, and C and N sequestration. This highly significant linear correlation suggests there are serious consequences to the loss of AMF from ecosystems.

}, keywords = {LTER-KNZ}, doi = {10.1111/j.1461-0248.2009.01303.x}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1461-0248.2009.01303.x}, author = {G.T. Wilson and C. W. Rice and Rillig, M.C. and Springer, A. and D.C. Hartnett} } @article {KNZ001212, title = {Responses of two bunchgrasses to nitrogen addition in tallgrass prairie: the role of bud bank demography}, journal = {American Journal of Botany}, volume = {95}, year = {2008}, pages = {672 -680}, abstract = {Growth of tallgrass prairie plants, many of which maintain substantial bud banks, can be limited by nitrogen (N), water, and/or light. We hypothesized that tallgrass prairie plants respond to increases in N through demographic effects on the bud bank. We tested the effects of a pulse of N on (1) bud bank demography, (2) plant reproductive allocation, and (3) ramet size. We parameterized matrix models, considering each genet as a population of plant parts. Nitrogen addition significantly impacted bud bank demography in two subdominant species of bunchgrass: Sporobolus heterolepis (a C4 grass) and Koeleria macrantha (a C3 grass), but had no effect on the size of individual ramets. Emergence from the bud bank and ramet population growth rates (λ) were significantly higher in S. heterolepis genets that received supplemental N. Nitrogen addition also affected the bud demography of K. macrantha, but N addition decreased rather than increased λ. Prospective and retrospective demographic analyses indicated that bud bank dynamics were the most important demographic processes driving plant responses to nutrient availability. Thus, the variation in productivity in these tallgrass prairie species is driven principally by the demography of the bud bank rather than by the physiology and growth of aboveground tillers. Improved understanding of bud bank dynamics may lead to improved predictive models of grassland responses to environmental changes such as altered N deposition and precipitation.}, keywords = {LTER-KNZ, kansas, Koeleria macrantha, Konza Prairie Long-Term Ecological Research Site, Meristem, Poaceae, Sporobolus heterolepis}, doi = {10.3732/ajb.2007277}, author = {Dalgleish, H.J. and Kula, A.R. and D.C. Hartnett and Sandercock, B.K.} } @article {KNZ001043, title = {Belowground bud banks increase along a precipitation gradient of the North American Great Plains: a test of the meristem limitation hypothesis}, journal = {New Phytologist}, volume = {171}, year = {2006}, pages = {81 -89}, abstract = {{\textbullet} In perennial grasslands, the below-ground population of meristems (bud bank) plays a fundamental role in plant population dynamics. Here, we tested the {\textquoteleft}meristem limitation hypothesis{\textquoteright} prediction {\textendash} that bud banks increase along an increasing precipitation/productivity gradient in North American grasslands {\textendash} and assessed the seasonal dynamics of bud banks. {\textbullet} We sampled bud and stem populations quarterly at six sites across a 1100 km gradient in central North America. {\textbullet} Bud banks increased with average annual precipitation, which explained 80\% of the variability between the sites. In addition, seasonal changes in grass bud banks were surprisingly similar across a 2.5-fold range in precipitation and a 4-fold range of productivity: densities peaked in March, decreased in June and increased slightly in September. {\textbullet} Increasing meristem limitation may constrain vegetation responses to inter-annual changes in resources. An important consequence of this is that biomes with large bud banks may be the most responsive to environmental change. If meristem limitation represents an important constraint on productivity responses to environmental variability, then bud banks must be considered in developing predictive models for grassland responses to environmental change.}, keywords = {LTER-KNZ}, doi = {10.1111/j.1469-8137.2006.01739.x}, author = {Dalgleish, H.J. and D.C. Hartnett} } @article {KNZ001044, title = {Bud banks of perennial savanna grasses in Botswana}, journal = {African Journal of Ecology}, volume = {44}, year = {2006}, pages = {256 -263}, abstract = {Three semi-arid savanna grasses in Botswana (Stipagrostis uniplumis, Eragrostis lehmanniana, and Aristida stipitata) were sampled to quantify their belowground bud banks during the dormant season and to estimate their relative allocation to vegetative and sexual reproduction. Bud banks of these African perennial caespitose grasses were also compared with four perennial caespitose grasses of semi-arid North American grasslands. The three African grasses each maintained approximately two buds per tiller and showed a high percentage (88{\textendash}99\%) of tillers producing seed. Only E. lehmanniana produced new aerial tillers from axillary buds at elevated nodes on the stem as well as from the belowground bud bank. Compared with species of North American grasslands, these African grasses produced fewer belowground buds but showed a much higher percentage of tillers producing seed. These patterns indicate relatively greater belowground meristem limitation, lower allocation to vegetative reproduction (tillering) and higher allocation to seed reproduction in these African grasses, although studies of more species are needed to assess the generality of this pattern. The management of savannas in ways that favour the maintenance of a reserve population of belowground buds may increase the ability of grasses to respond to pulses of resource availability, increase their compensatory growth capacity following grazing or drought, and decrease the invasibility of these plant communities by exotic species, whereas maintaining allocation to sexual reproduction may be important for conserving genetic variation and enhancing their capacity to adapt to environmental change.}, keywords = {LTER-KNZ, clonal plants, meristems, Plant demography, reproductive strategy, Vegetative reproduction}, doi = {10.1111/j.1365-2028.2006.00646.x}, author = {D.C. Hartnett and Setshogo, M.P. and Dalgleish, H.J.} } @booklet {KNZ001045, title = {Enhancing collaborative research on the environment in sub-Saharan Africa}, journal = {OISE National Science Foundation Report}, year = {2006}, pages = {1 -99}, keywords = {LTER-KNZ}, author = {D.C. Hartnett and Semazzi, F.H.M.} } @article {KNZ001046, title = {Mycorrhizal-mediated phosphorus transfer between tallgrass prairie plants Sorghastrum nutans and Artemisia ludoviciana}, journal = {Functional Ecology}, volume = {20}, year = {2006}, pages = {427 -435}, abstract = {1A glasshouse 32P-labelling study examined arbuscular mycorrhizal (AM)-mediated transfer of phosphorus between individuals of two tallgrass prairie species, an obligately mycotrophic grass (Sorghastrum nutans Vitm.) and a facultatively mycotrophic forb (Artemisia ludoviciana Nutt.). 2Regardless of which species served as donor, 32P was transferred between both intra- and interspecific neighbours via AM mycelia. However, nutrient transfer via AM fungi was not uniform between neighbouring species. 3Conservative estimates indicate that interplant transfer via AM fungi accounted for >50\% of the total 32P acquisition by S. nutans, but accounted for only 20\% of 32P uptake into A. ludoviciana. 4While this study did not show conclusively that a common mycelial network acted as a conduit for nutrient transfer, it clearly demonstrated that mycorrhizae facilitated transfer. 5The results indicate that differential movement of plant resources via AM mycelium may be a mechanism whereby a dominant, highly mycotrophic grass extends competitive advantage over a less mycotrophic, subdominant forb species in grasslands.}, keywords = {LTER-KNZ}, doi = {10.1111/j.1365-2435.2006.01134.x}, author = {G.T. Wilson and D.C. Hartnett and C. W. Rice} } @article {KNZ00938, title = {The role of seed and vegetative reproduction in plant recruitment and demography in tallgrass prairie}, journal = {Plant Ecology}, volume = {187}, year = {2006}, pages = {163 -177}, abstract = {Recruitment, establishment and survivorship of seed- and vegetatively-derived shoots were quantified biweekly in annually burned and infrequently burned tallgrass prairie to investigate the contributions of seed and vegetative reproduction to the maintenance and dynamics of tallgrass prairie plant populations, the demography of seedlings and ramets, and the influence of fire on the demography of grasses and forbs. Clonally produced grass and forb ramets comprised >99\%of all established shoots present at the end of the growing season, whereas established seedlings accounted for <1\%,emphasizing the rarity of successful seedling establishment and the importance of vegetative reproduction in driving the annual regeneration and dynamics of aboveground plant populations in tallgrass prairie. Most recruitment from vegetative reproduction occurred early in the growing season and was higher in annually burned than infrequently burned sites, although low levels of new stem recruitment occurred continuously throughout the growing season. Peak recruitment on annually burned prairie coincided with peak recruitment of the dominant C4 grasses Andropogon gerardii and Sorghastrum nutans prior to prescribed spring fire, with a second peak in recruitment occurring following fire. On infrequently burned prairie, grass and forb recruitment was highest in early April and declined steadily through May. The naturalized C3 grass, Poa pratensis, was responsible for most of the early recruitment on unburned sites, whereas A. gerardii contributed most to recruitment later in May. Infrequently burned prairie was dominated by these two grasses and contained a larger forb component than annually burned prairie. The principal demographic effect of fire was on ramet natality rather than mortality. Fire regime, plant functional group, or timing of cohort emergence before or after fire did not affect ramet survivorship. C4 grass shoots that emerged early and were damaged by fire showed similar survivorship patterns to tillers that emerged after fire. Differences in species composition between annually burned and infrequently burned prairie are driven by fire effects on vegetative reproduction and appear to be related principally to the effect of fire and detritus accumulation on the development of belowground vegetative meristems of C4 grasses and their emergence dynamics.}, keywords = {LTER-KNZ, fire ecology, grassland, Rhizomes, Sexual reproduction, Survivorship}, doi = {10.1007/s11258-005-0975-y}, author = {Benson, E. and D.C. Hartnett} } @article {KNZ001042, title = {The use of pasture reflectance characteristics and arbuscular mycorrhizal root colonization to predict pasture characteristics of tallgrass prairie grazed by cattle and bison}, journal = {Grass and Forage Science}, volume = {61}, year = {2006}, pages = {32 -41}, abstract = {An experiment was conducted to evaluate the potential for using arbuscular mycorrhizal fungal (AMF) root colonization and pasture reflectance characteristics as indicators of changes in tallgrass prairie vegetation resulting from differences in grazing history. The experiment was conducted within the context of a separate long-term experiment in which eight 4{\textperiodcentered}9-ha pastures were grazed by either bison or cattle for nine consecutive years. Two separate ungrazed pastures were selected for comparison with grazed areas on the basis of similarity in burning regime, vegetation, soil and topographic characteristics. Four 45 m-long transects were located in the upland sites within each pasture, and four plots were clipped to ground level along each transect. Reflectance readings were taken with a hand-held radiometer at each sampling location and a soil core was collected within each plot for analysis of AMF root colonization. Reflectance readings at sixteen different wavelengths were used directly as inputs during multiple regression development or were transformed into each of three vegetation indices (normalized difference vegetation index, soil-adjusted vegetation index and wide-dynamic-range vegetation index) and used in simple linear regressions. Ungrazed pastures were characterized by higher (P < 0{\textperiodcentered}01) grass biomass, total biomass and canopy height than grazed pastures, but had a lower proportional abundance of forbs (P < 0{\textperiodcentered}01) and amounts of forb biomass (P = 0{\textperiodcentered}04). Species of herbivore did not significantly influence above-ground characteristics that were measured. In general, AMF root colonization was relatively small and was not significantly affected by treatment and, accordingly, the variation was insufficient to test its potential as an indicator of grazing effects on vegetation or its potential relationship with pasture reflectance. Multiple regression equations based on individual wavelength reflectance values explained significantly more of the variation in above-ground vegetation characteristics than did simple regressions using vegetation indices as predictor variables (r2 values from 0{\textperiodcentered}36 to 0{\textperiodcentered}46 vs. 0{\textperiodcentered}11 to 0{\textperiodcentered}27) and have the potential to predict above-ground vegetation characteristics in heterogeneous rangelands.}, keywords = {LTER-KNZ, Arbuscular mycorrhizal fungi, bison, Cattle, pasture characteristics, reflectance methods, tallgrass prairie}, doi = {10.1111/j.1365-2494.2006.00505.x}, author = {Villarreal, M. and Cochran, R.C. and Johnson, D.E. and Towne, E.G. and G.T. Wilson and D.C. Hartnett and Goodin, D.G.} } @article {KNZ00976, title = {Mycorrhizal symbiosis and insect herbivory in tallgrass prairie microcosms}, journal = {Ecology Letters}, volume = {81}, year = {2005}, pages = {61 -69}, keywords = {LTER-KNZ}, author = {Kula, A.R. and D.C. Hartnett and G.T. Wilson} } @article {KNZ00975, title = {Vegetationtrends in tallgrass prairie from bison and cattle grazing}, journal = {Ecological Applications}, volume = {15}, year = {2005}, pages = {1550 -1559}, abstract = {Comparisons between how bison and cattle grazing affect the plant community are understood poorly because of confounding differences in how the herbivores are typically managed. This 10-year study compared vegetation changes in Kansas (USA) tallgrass prairie that was burned and grazed season-long at a moderate stocking rate by either bison or cattle. We held management practices constant between the herbivores and equalized grazing pressure by matching animals so that the total body mass in all pastures was similar each year. Trends in species cover and diversity indices in the bison and cattle pastures were compared with ungrazed prairie that also was burned annually. We found that little bluestem (Schizachyrium scoparium) cover decreased over time in bison pastures, and big bluestem (Andropogon gerardii) cover increased over time in cattle pastures. Grazing by either herbivore increased the canopy cover of annual forbs, perennial forbs, and cool-season graminoids, but both annual and perennial forb cover increased at a greater rate in bison pastures than in cattle pastures. Missouri goldenrod (Solidago missouriensis) and heath aster (Symphyotrichum ericoides) were primarily responsible for the increased forb cover in grazed pastures. Species richness at both small (10 m2) and large (200 m2) spatial scales increased at a greater rate in bison pastures than in cattle pastures, but richness did not change through time in ungrazed prairie. The number of annual forb species was significantly higher in bison pastures than in pastures grazed by cattle. Residual graminoid biomass at the end of the grazing season was lower in bison pastures than in cattle pastures, whereas forb residuum increased over time at a greater rate in pastures grazed by bison than in pastures grazed by cattle. Although bison and cattle differentially altered some vegetation components, the plant communities in bison and cattle pastures were 85\% similar after 10 years of grazing. We conclude that most measurable differences between bison-grazed and cattle-grazed pastures in tallgrass prairie are relatively minor, and differences in how the herbivores are typically managed may play a larger role in their impact on prairie vegetation than differences between the species.}, keywords = {LTER-KNZ}, doi = {10.1890/04-1958}, author = {Towne, E.G. and D.C. Hartnett and Cochran, R.C.} } @article {KNZ00876, title = {Belowground bud banks and meristem limitation in tallgrass prairie plant populations}, journal = {American Journal of Botany}, volume = {91}, year = {2004}, pages = {416 -421}, abstract = {Rhizome meristem populations were sampled in tallgrass prairie to quantify the size, grass : forb composition, and temporal and spatial variability of the soil bud bank and to compare fire effects on bud bank and seed bank composition. Soil cores (10.5 cm diameter, 15 cm deep) were collected from replicate annually and infrequently burned tallgrass prairie sites, and intact rhizomes and rhizome buds were censused. Bud bank densities ranged from approximately 600 to 1800 meristems/m2 among sites and had high spatial and seasonal variability. In annually burned prairie, the total bud bank density was two-fold greater and the grass : forb meristem ratio was more than 30-fold greater than that of infrequently burned prairie. These patterns are opposite those observed in soil seed banks at this site. The rhizome population in annually burned prairie was 34\% larger than the established aboveground tiller population. By contrast, the bud bank density in unburned prairie was significantly lower than aboveground stem densities, indicating possible belowground meristem limitation of stem density and net primary production on infrequently burned prairie. The patterns observed in this study suggest that the densities and dynamics of tallgrass prairie plant populations, as well as their response to disturbance (e.g., fire and grazing) and climatic variability, may be mediated principally through effects on the demography of belowground bud populations. Patterns of seed reproduction and seed bank populations have little influence on short-term aboveground population dynamics of tallgrass prairie perennials.}, keywords = {LTER-KNZ, fire, Rhizomes, Seed bank, tallgrass prairie}, doi = {10.3732/ajb.91.3.416}, author = {Benson, E. and D.C. Hartnett and Mann, K.} } @article {KNZ00900, title = {Fire effects on mycorrhizal symbiosis and root system architecture in southern African savanna grasses}, journal = {African Journal of Ecology}, volume = {42}, year = {2004}, pages = {1 -10}, abstract = {Mycorrhizal symbiosis is a key factor influencing aspects of grassland and savanna structure and functioning including plant growth, competition, population and community dynamics, and responses to fire and herbivory. This study assessed the effects of fire on mycorrhizal symbiosis and root system architecture (RSA) in South African savanna grasses. Eighteen grass species were sampled across contrasting fire frequency treatments in the Kruger National Park experimental burn plots. All eighteen species studied were highly colonized by arbuscular mycorrhizal fungi (AMF). Both mycorrhizal symbiosis and RSA were strongly affected by fire, with an increase in AMF colonization and a decrease in root branching and fine root development with decreasing fire frequency. Greater water limitation in frequently burned savanna may result in greater fine root development, thus reducing plant dependency on AMF for acquisition of soil resources. Reduced mycorrhizal colonization in frequently burned savanna may also be driven by higher phosphorus : nitrogen ratios, or indirect effects related to higher grazing intensities in frequently burned sites.}, keywords = {LTER-KNZ, fire, Grasses, mycorrhizas, root architecture, Savannas}, doi = {10.1111/j.1365-2028.2004.00533.x}, author = {D.C. Hartnett and Potgieter, A.L.F. and G.T. Wilson} } @article {KNZ00879, title = {Grazing management effects on plant species diversity in tallgrass prairie}, journal = {Journal of Range Management}, volume = {57}, year = {2004}, pages = {58 -65}, abstract = {A 6-year study was conducted in tallgrass prairie to assess the effects of grazing management (cattle stocking densities and grazing systems) on plant community composition and diversity. Treatments included sites grazed season-long (May to October) at 3 stocking densities (3.8, 2.8, and 1.8 hectares per animal unit), ungrazed control sites, and sites under a late-season rest rotation grazing system at this same range of stocking densities. Plant communities were sampled twice each season using a nearest-point procedure. Native plant species diversity, species richness, and growth form diversity were significantly higher in grazed compared to ungrazed prairie, and diversity was greatest at the highest stocking density. This enhancement of plant species diversity under grazing was not a result of increased frequency of weedy/exotic species. There were no significant effects of grazing system on plant diversity, nor any significant stocking density {\texttimes} grazing system interactions, indicating that animal density is a key management variable influencing plant species diversity and composition in tallgrass prairie and that effects of animal density override effects of grazing systems. Increasing cattle stocking densities decreased the abundance of the dominant perennial tall grasses, and increased abundance of the C4 perennial mid-grasses. The frequency of perennial forbs was relatively stable across grazing treatments. Abundance of annual forbs varied among years and grazing treatments. In half of the years sampled, annual forbs showed the highest frequency under intermediate stocking density. Patterns of responses among plant groups suggest that some species may respond principally to direct effects of grazers and others may respond to indirect effects of grazers on competitive relationships or on the spatial patterns of fuel loads and fires. Thus, this study suggests that large grazer densities, fire, and annual climatic variability interact to influence patterns of plant community composition and diversity in tallgrass prairie. Effects of varying management such as stocking densities and grazing systems on plant species diversity and the relative abundances of different plant growth forms or functional groups may have important consequences for grassland community stability and ecosystem function.}, keywords = {LTER-KNZ, Biodiversity, cattle grazing, Flint Hills, grazing systems, plant ecology, range management, stocking rates}, doi = {10.2111/1551-5028(2004)057[0058:GMEOPS]2.0.CO;2}, author = {Hickman, K.R. and D.C. Hartnett and Cochran, R.C. and Owensby, C.E.} } @article {KNZ00937, title = {Interactive effects of burn regime and bison activity on tallgrass prairie vegetation}, journal = {American Midland Naturalist}, volume = {152}, year = {2004}, pages = {237 -247}, keywords = {LTER-KNZ}, author = {Trager, M. and G.T. Wilson and D.C. Hartnett} } @article {KNZ009, title = {Effects of grazing intensity on growth, reproduction, and abundances of three palatable forbs in Kansas tallgrass prairie}, journal = {Plant Ecology}, volume = {159}, year = {2002}, pages = {23 -33}, abstract = {

The effects of different intensities of cattle grazing on the aboveground growth, reproduction, and abundances of three palatable forbs were studied in native tallgrass prairie. Populations of Aster ericoides, Ruellia humilis, and Amorpha canescens were sampled at peak flowering during the 1993-1995 growing seasons in four annually-burned sites varying in cattle stocking density [ungrazed, low, moderate, high]. The three forbs exhibitedreduced shoot growth and/or reproduction under moderate to heavy grazing, and in no case did grazing increase any measure of plant performance. Ruellia showed reduced shoot height and biomass, percentage of stemsflowering, and reproductive biomass in response to grazing. Aster showed decreases in shoot biomass and height with grazing. Amorpha showed no change in shoot or reproductive biomass, but a decrease in percent of flowering stems and in reproductive allocation with grazing. Patterns in the percentage of stems grazed indicated generally high but variable palatability among these species. By contrast, the three species showedinconsistent population response to grazing. Abundance (frequency) of all three species indicated no short-term change between years in response to grazing intensity. Responses of these species differ considerably from those of most other perennial tallgrass prairie forbs that are unpalatable, unconsumed, and increase in performance (e.g. size, abundance) due to release from competition from the dominant grasses under ungulate grazing. The results demonstrate that immediate aboveground growth and reproductiveresponses of established adults to grazing are not good predictors of grazer effects on population abundances in tallgrass prairie.

}, keywords = {LTER-KNZ, flowering}, doi = {10.1023/A:1015534721939}, url = {http://ipsapp008.lwwonline.com/content/getfile/5220/57/6/fulltext.pdf}, author = {Hickman, K.R. and D.C. Hartnett} } @inbook {KNZ00986, title = {Fire behaviour as a key factor in the fire ecology of African grasslands and savannas}, booktitle = {Forest Fire Research and Wildland Fire}, year = {2002}, pages = {204 -}, publisher = {Millpress, Rotterdam Netherlands}, organization = {Millpress, Rotterdam Netherlands}, abstract = {

The effect of fire on natural ecosystems involves the response of living organisms to the release of heat energy through the combustion of plant material. The manner in which and the factors that influence the release of heat energy, involves the study of fire behaviour. In Africa there is a serious deficiency of knowledge concerning the behaviour of fires and this is particularly applicable to the savanna and grassland areas of the continent. Virtually no attempt has been made to quantify the dynamics of the release of heat energy during a fire and the subsequent response of plants to it. The determination of such relationships helps explain many of the apparently inexplicable effects of fire that are often cited in the literature. Research on the effects of fire has been conducted throughout the grassland and savanna areas of Africa, particularly in southern Africa, since the early period of the 20th century. An interesting feature about these early investigations and subsequent research up until 1971, was that it focused on the effects of season and frequency of burning on the forage production potential of the grass sward and the ratio of bush to grass in savanna areas However, in 1971 a conference was convened in the United States of America in Florida, by the Tall Timbers Research Station on the theme of \"Fire in Africa\". The major benefit that accrued from this conference was the realization that in Africa the study of fire behaviour and its effects on the ecosystem, as described by type and intensity of fire, had been largely ignored in all the fire research that had been conducted up until that time. As a consequence a research program was initiated in South Africa and later extended to East Africa, to characterise the behaviour of fires burning in savanna and grassland vegetation and determine the effect of type and intensity of fire on the vegetation. The overall effect of type of fire is that surface head fires and crown fires have the least effect on grasses and have the potential to have the greatest effect on trees. This is because the heat is released above ground level away from the growing points of the grasses and closest to the growing points of the trees. Conversely, surface back fires have the opposite effect on grass and tree vegetation. This is because the heat is released close to ground level where the growing points of grasses are located and away from the growing points of the trees in the canopy. The overall effect of fire intensity is that grasses are generally not sensitive to increasing fire intensities because their growing points are located close to ground level away from the release of heat energy. Conversely trees are sensitive to increasing fire intensities because their growing points are generally exposed to the release of heat energy in the canopy of the trees. These effects explain why intense fires favour the development of grassland and open savannas and vice versa. The behaviour of surface head and back fires is currently being compared in southern African savannas and tall grass prairies in North America and results indicate that fires burning in grass dominated communities behave similarly and may therefore have similar effects on grass and tree vegetation globally.

}, keywords = {LTER-KNZ, African grasslands, American prairies, fire, Savannas}, author = {Trollope, W.S.W. and Trollope, L.A. and D.C. Hartnett}, editor = {Viegas, D.X.} } @article {KNZ00829, title = {The role of mycorrhizas in plant community structure and dynamics: lessons from grasslands}, journal = {Plant and Soil}, volume = {244}, year = {2002}, pages = {319 -331}, abstract = {Research on the mycorrhizal associations over the past several decades has yielded increased understanding and appreciation of the important role of this symbiosis in the functioning and performance of plants in a wide array of terrestrial ecosystems. We now understand that the role of mycorrhizal fungi extends beyond the symbiotic acquisition of phosphorus for the host plant and reciprocal carbon provision from the host to fungus. Additional effects of mycorrhizal fungi on the functioning of their host plants including increased disease resistance, improved water relations, acquisition of other soil nutrients, and alterations in other soil physico-chemical properties have been documented. Other aspects of the ecology of mycorrhizas, including variation in the costs and benefits of carbon and nutrient exchange, the ecological significance of mycelial networks, the role of mycorrhizal symbiosis in multi-species interactions, and the extent and consequences of host-specificity in these associations have also recently been explored.}, keywords = {LTER-KNZ}, doi = {10.1007/978-94-017-1284-2_31}, author = {D.C. Hartnett and G.T. Wilson} } @article {KNZ00828, title = {Variation in grazing tolerance among three tallgrass prairie plant species}, journal = {American Journal of Botany}, volume = {89}, year = {2002}, pages = {1634 -1643}, abstract = {Three tallgrass prairie plant species, two common perennial forbs (Artemisia ludoviciana and Aster ericoides [Asteraceae]) and a dominant C4 perennial grass (Sorghastrum nutans) were studied under field and greenhouse conditions to evaluate interspecific variation in grazing tolerance (compensatory growth capacity). Adaptation to ungulate grazing was also assessed by comparing defoliation responses of plants from populations with a 25-yr history of no grazing or moderate ungulate grazing. Under field conditions, all three species showed significant reductions in shoot relative growth rates (RGR), biomass, and reproduction with defoliation. In the two forbs, clipping resulted in negative shoot RGR and reductions in both number and length of shoot branches per ramet. Sorghastrum nutans maintained positive RGR under defoliation due to a compensatory increase in leaf production. Defoliation reduced rhizome production in A. ericoides and S. nutans, but not in A. ludoviciana. Clipping significantly reduced sexual reproductive allocation in all three species, although S. nutans showed a smaller reduction than the forbs. All three species showed similar responses to defoliation in burned and unburned sites. Under greenhouse conditions, a similar clipping regimen resulted in smaller reductions in growth and reproduction than those observed in the field. For all three species, the grazing tolerance indices calculated under natural field conditions were significantly lower than those estimated from greenhouse-grown plants, and the interspecific patterns of grazing tolerance were different. Aster ericoides exhibited the highest overall defoliation tolerance under greenhouse conditions, followed by S. nutans. Artemisia ludoviciana, the only study species that is typically not grazed by ungulates in the field, showed the lowest grazing tolerance. In the field experiment S. nutans showed the highest grazing tolerance and the two forbs had similar low tolerance indices. These patterns indicate that, despite high compensatory growth potential, limited resource availability and competition in the field significantly reduce the degree of compensation and alter interspecific differences in grazing tolerance among prairie plants. In all three species, defoliation suppressed sexual reproduction more than growth or vegetative reproduction. Significant interactions between plant responses to defoliation and site of origin (historically grazed or ungrazed sites) for some response variables (root/shoot ratios, rhizome bud initiation, and reproductive allocation) indicated some degree of population differentiation and genetic adaptation in response to a relatively short history of ungulate grazing pressure. The results of this study indicate that patterns of grazing tolerance in tallgrass prairie are both genetically based and also environmentally dependent. }, keywords = {LTER-KNZ, Ambrosia ludoviciana, Aster ericoides, compensatory growth, forbs, Grasses, grazing tolerance, Sorghastrum nutans, tallgrass prairie}, doi = {10.3732/ajb.89.10.1634}, author = {Damhoureyeh, S.A. and D.C. Hartnett} } @article {KNZ0017, title = {Effects of mycorrhizas on growth and demography of tallgrass prairie forbs}, journal = {American Journal of Botany}, volume = {88}, year = {2001}, pages = {1452 -1457}, abstract = {The effects of arbuscular mycorrhizal (AM) symbiosis on ramet and genet densities, vegetative growth rates, and flowering of three forb species were studied in native tallgrass prairie in northeastern Kansas. Mycorrhizal activity was experimentally suppressed for six growing seasons on replicate plots in an annually burned and an infrequently burned watershed with the fungicide benomyl. Benomyl reduced mycorrhizal root colonization to an average of 4.2\%, approximately a two-thirds reduction relative to controls (13.7\% colonization). Mycorrhizae influenced the population structure of these forbs. Although mycorrhizal suppression had no long-term effect on genet densities and no effect on ramet survivorship throughout the growing season, the number of ramets per individual was significantly increased such that ramet densities of all three species were approximately doubled in response to long-term mycorrhizal suppression. Effects of mycorrhizae on ramet growth and reproduction varied among species. Ramet growth rates, biomass, and flowering of Salvia azurea were greater in plots with active mycorrhizal symbiosis, whereas mycorrhizae reduced ramet growth rates and biomass of Artemesia ludoviciana. Aster sericeus ramet growth rates and biomass were unaffected by the fungicide applications, but its flowering was reduced.The pattern of responses of these three species to mycorrhizae differed considerably between the two sites of contrasting fire regime, indicating that the interaction of fire-induced shifts in resource availability and mycorrhizal symbiosis together modulates plant responses and the intensity and patterns of interspecific competition between and among tallgrass prairie grass and forb species. Further, the results indicate that effects of mycorrhizae on community structure are a result of interspecific differences in the balance between direct positive effects of the symbiosis on host plant performance and indirect negative effects mediated through altered competitive interactions.}, keywords = {LTER-KNZ, demography, forb, tallgrass prairie}, url = {http://www.ncbi.nlm.nih.gov/pubmed/21669678}, author = {G.T. Wilson and D.C. Hartnett and M.D. Smith and Kobbeman, K.} } @article {KNZ00784, title = {Effects of plains pocket gopher (Geomys bursarius) disturbances on tallgrass-prairie community structure}, journal = {American Midland Naturalist}, volume = {145}, year = {2001}, pages = {344 -357}, abstract = {Our objective was to evaluate the effects of soil disturbances created by the plains pocket gopher (Geomys bursarius) on the structure of a tallgrass-prairie plant community. We predicted that soil mounds and burrows would provide sites for the establishment of subordinate plant species, thereby increasing regional plant community richness in this ecosystem that is highly dominated by perennial C4 tallgrasses. Our results, however, revealed that plant species richness and biomass were temporarily decreased or unaffected in areas disturbed by gophers. Moreover, the species found locally on mounds and burrows were a subset of the dominant plants present in the undisturbed plant community and graminoids were more frequent on disturbances than forbs. Our results indicate that perennial graminoids predominate in the rapid recovery of vegetation on pocket gopher mounds and burrows. This preempts the establishment of less frequent forbs and, contrary to our predictions, decreases plant community richness.}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.1674/0003-0031(2001)145[0344:EOPPGG]2.0.CO;2}, author = {Rogers, W.E. and D.C. Hartnett and Elder, B.} } @article {KNZ00768, title = {Effects of ungulate grazers on arbuscular mycorrhizal symbiosis and fungal community structure in tallgrass prairie}, journal = {Mycology}, volume = {93}, year = {2001}, pages = {233 -242}, abstract = {Complex interactions among mycorrhizal fungi, plants, and herbivores occur in grasslands. Grazing of aboveground vegetation may influence plants directly and indirectly through the alteration of mycorrhizal symbiosis and other below-ground processes, and mycorrhizae in turn can influence plant responses to defoliation. An understanding of these interactions is important to our understanding of the dynamics of plant and fungal communities and to the sound management and conservation of grass- land ecosystems. In this study, the effects of grazing in tallgrass prairie on mycorrhizal colonization of plant roots, fungal community composition, and ex- traradical mycorrhizal hyphal (EMH) development were examined. In October 1994 and 1995 rhizo- sphere samples were taken at different topographical positions in tallgrass prairie sites grazed for several years by cattle at varying intensities, in ungrazed sites, and inside and outside permanent 25-m2 exclosures at each site. Spores of 19 species of AM fungi were encountered in these sites, and Glomus heterosporum was the most abundant species present. Moderate and intense grazing increased root colonization by mycorrhizal fungi in both years of this study. Similar root colonization levels inside and outside permanent exclosures in the ungrazed sites indicated no confounding effects of the exclosure structure itself. In 1995, EMH development was also increased under intense grazing. AM fungal species diversity (based on AM fungal spores present) decreased with grazing under both moderate and high grazer densities in both years. Different fungal species varied in abun- dance with topographical position, however topography did not significantly affect AM fungal spore species diversity, mycorrhizal root colonization or EMH development in either year. Although overall total spore density was unaffected by grazing intensity or soil type, several individual species increased or decreased in response to these factors. These results suggest that defoliation alters plant resources which stimulates greater development of mycorrhizal symbiosis. The shifts in fungal species composition and decrease in diversity with grazing also indicates that defoliation, or alteration of the soil microenviron- ment by grazers, favors certain species of grazing- adapted AM fungi that increase under grazed conditions. The high mycorrhizal dependency of many tallgrass prairie grasses and these results together suggest significant interactions between plant-grazer and plant-fungal relationships in tallgrass prairie. In addition to direct effects of herbivory, our results indicate that grazers may influence grassland plants in- directly through alterations in soil communities and in mycorrhizal symbiosis. }, keywords = {LTER-KNZ, fungal communities, fungal diversity, Glomus, hyphal development, mycorrhizae}, url = {http://www.jstor.org/stable/3761643?seq=1$\#$page_scan_tab_contents}, author = {Eom, A.H. and G.T. Wilson and D.C. Hartnett} } @article {KNZ00785, title = {Temporal vegetation dynamics and recolonization mechanisms on different-sized soil disturbances in tallgrass prairie}, journal = {American Journal of Botany}, volume = {88}, year = {2001}, pages = {1634 -1642}, abstract = {Assessing the various mechanisms by which plants revegetate disturbances is important for understanding the effects of disturbances on plant population dynamics, plant community structure, community assembly processes, and ecosystem function. We initiated a 2-yr experiment examining temporal vegetation dynamics and mechanisms of recolonization on different-sized soil disturbances created to simulate pocket gopher mounds in North American tallgrass prairie. Treatments were designed to assess potential contributions of the seed rain, soil seed bank, clonal propagation from the edges of a soil mound, and regrowth of buried plants. Small mounds were more rapidly recolonized than large mounds. Vegetative regrowth strategies were the dominant recolonization mechanisms, while the seed rain was considerably less important in maintaining the diversity of forbs and annuals than previously believed. All recolonization mechanisms influenced plant succession, but stem densities and plant mass on soil mounds remained significantly lower than undisturbed controls after two growing seasons. Because natural pocket gopher mounds are indistinguishable from undisturbed areas after two seasons, these results suggest that multiple modes of recruitment concurrently, albeit differentially, contribute to the recolonization of soil disturbances and influence tallgrass prairie plant community structure and successional dynamics.}, keywords = {LTER-KNZ, tallgrass prairie}, url = {http://www.ncbi.nlm.nih.gov/pubmed/21669697}, author = {Rogers, W.E. and D.C. Hartnett} } @article {KNZ0016, title = {Vegetation responses to different spatial patterns of soil disturbances in burned and unburned tallgrass prairie}, journal = {Plant Ecology}, volume = {155}, year = {2001}, pages = {99 -109}, abstract = {Pocket gopher (Geomyidae) disturbances are created in spatiallypredictable patterns. This may influence resource heterogeneity and affectgrassland vegetation in a unique manner. We attempt to determine the extent towhich density and spatial pattern of soil disturbances influence tallgrassprairie plant community structure and determine how these disturbances interactwith fire. To investigate the effects of explicit disturbance patterns we createdsimulated pocket gopher burrows and mounds in various spatial patterns.Simulated burrows were drilled into the soil at different densities inreplicated plots of burned and unburned prairie. Separate plots of simulatedmounds were created in burned and unburned prairie at low, medium, or high mounddensities in clumped, uniform, or random spatial dispersions. In both burned and unburned plots, increased burrow density decreasedgraminoid biomass and increased forb biomass. Total-plant and graminoid biomasswere higher in burned than unburned plots while forb biomass was higher inunburned plots. Total-plant species richness was not significantly affected byburrow density or burning treatments, but graminoid species richness increasedin unburned plots and forb species richness increased in burned plots. Plant species richness was temporarily reduced directly on mounddisturbances compared to undisturbed prairie. Over time and at larger samplingscales, the interaction of fire and mound disturbance patterns significantlyaffected total-plant and graminoid species richness. The principal effect inburned and unburned prairie was decreased total-plant and graminoid speciesrichness with increased mound disturbance intensity. Although species richness at small patch scales was not increased by anyintensity of disturbance and species composition was not altered by theestablishment of a unique guild of disturbance colonizing plants, our studyrevealed that interactions between soil disturbances and fire alter the plantcommunity dominance structure of North American tallgrass prairie primarily viachanges to graminoids. Moreover, these effects become increasingly pronouncedover time and at larger spatial sampling scales.}, keywords = {LTER-KNZ, pattern, soil, spatial, tallgrass prairie, vegetation}, doi = {10.1023/A:1013264308786}, author = {Rogers, W.E. and D.C. Hartnett} } @article {KNZ00749, title = {Effects of long-term fungicide application on microbial processes in tallgrass prairie soils}, journal = {Soil Biology \& Biochemistry}, volume = {32}, year = {2000}, pages = {935 -946}, abstract = {Several studies investigating the role of arbuscular mycorrhizal (AM) fungi in plant communities have included manipulations of AM fungal symbiosis using the fungicide benomyl. The objectives of this study were to evaluate the potential non-target effects of benomyl on soil biota and nutrient cycling in tallgrass prairie and to determine how mycorrhizae may influence these belowground properties. To accomplish these objectives, soil samples were collected during the 1996{\textendash}1997 growing seasons from long-term benomyl-treated plots established on tallgrass prairie (Manhattan, KS) in 1991, and the following measurements were made: total bacterial and fungal biomass; abundance of nematodes; microbial biomass carbon and nitrogen; substrate-induced respiration; and potentially mineralizable C and N. Long-term benomyl applications resulted in an 80\% reduction in mycorrhizal root colonization. By reducing root colonization, benomyl applications resulted in significant decreases in total bacterial biomass and abundance of fungal-feeding and predatory nematodes (20, 12 and 33\% reductions compared to control, respectively). Total microbial potential activity (i.e., substrate-induced respiration) increased by 10\% with benomyl treatment, whereas the relative contribution of fungi to total microbial activity decreased significantly with benomyl applications. In addition, microbial biomass C increased from 1364 ({\textpm} 51.2 SE) to 1485 ({\textpm} 51.2 SE) with benomyl treatment, and total carbon increased significantly (\~{}8\%) only in annually burned soils treated with benomyl. The magnitude of benomyl effects on soil components and processes were small (<33\% change with benomyl) relative to effects on mycorrhizal root colonization (80\% decrease with benomyl). These results indicate that rather than having large non-target effects, benomyl applications principally affect mycorrhizal root colonization, thereby indirectly influencing soil biota and nutrient availability. Results also indicate that mycorrhizal fungi play an important role in altering the availability and flow of carbon in prairie soil and may influence the composition and abundance of groups of some soil biota. Changes in soil organisms and nutrient availability associated with altered mycorrhizal symbiosis may influence aboveground plant species responses to mycorrhizal suppression, but further research is needed to understand these potential effects.}, keywords = {LTER-KNZ, Arbuscular mycorrhizal fungi, Benomyl, carbon, Microbial biomass, Nematodes, nitrogen}, doi = {10.1016/S0038-0717(99)00223-0}, author = {M.D. Smith and D.C. Hartnett and C. W. Rice} } @article {KNZ00732, title = {Host plant species effects on arbuscular mycorrhizal fungal communities in tallgrass prairie}, journal = {Oecologia}, volume = {122}, year = {2000}, pages = {435 -444}, abstract = {Symbiotic associations between plants and arbuscular mycorrhizal (AM) fungi are ubiquitous in many herbaceous plant communities and can have large effects on these communities and ecosystem processes. The extent of species-specificity between these plant and fungal symbionts in nature is poorly known, yet reciprocal effects of the composition of plant and soil microbe communities is an important assumption of recent theoretical models of plant community structure. In grassland ecosystems, host plant species may have an important role in determining development and sporulation of AM fungi and patterns of fungal species composition and diversity. In this study, the effects of five different host plant species [Poa pratensis L., Sporobolus heterolepis (A. Gray) A. Gray, Panicum virgatum L., Baptisia bracteata Muhl. ex Ell., Solidago missouriensis Nutt.] on spore communities of AM fungi in tallgrass prairie were examined. Spore abundances and species composition of fungal communities of soil samples collected from patches within tallgrass prairie were significantly influenced by the host plant species that dominated the patch. The AM fungal spore community associated with B. bracteata showed the highest species diversity and the fungi associated with Pa. virgatum showed the lowest diversity. Results from sorghum trap cultures using soil collected from under different host plant species showed differential sporulations of AM fungal species. In addition, a greenhouse study was conducted in which different host plant species were grown in similar tallgrass prairie soil. After 4 months of growth, AM fungal species composition was significantly different beneath each host species. These results strongly suggest that AM fungi show some degree of host-specificity and are not randomly distributed in tallgrass prairie. The demonstration that host plant species composition influences AM fungal species composition provides support for current feedback models predicting strong regulatory effects of soil communities on plant community structure. Differential responses of AM fungi to host plant species may also play an important role in the regulation of species composition and diversity in AM fungal communities.}, keywords = {LTER-KNZ, Arbuscular mycorrhizal fungi, fungal diversity, Grasslands, Host specificity, Soil communities}, doi = {10.1007/s004420050050}, author = {Eom, A.H. and D.C. Hartnett and G.T. Wilson} } @article {KNZ00688, title = {Designs for greenhouse studies of interactions between plants}, journal = {Journal of Ecology}, volume = {87}, year = {1999}, pages = {1 -16}, abstract = {1 Designs for greenhouse studies of interactions between plants are reviewed and recommendations for their use are provided. 2 Papers published over a 10-year period showed the replacement series design to be the most popular, especially in studying crop{\textendash}weed interactions. Fifty per cent of the studies involved only two species, although studies testing the interaction between different genotypes of only a few species were also popular. 3 Limitations imposed by the choice of design, the variables measured, and the analysis used on the range of inferences that may be validly drawn from the experiment are frequently not well understood or appropriate for the questions that appear to be addressed. One example is the failure to distinguish the outcome of competition (the long-term outcome of interaction) and the effects of species on each other. 4 Studies in which only final yield is measured are severely limited as to the inferences which may be drawn. Effects due to interspecific interaction during the course of the experiment cannot then be separated from pre-existing differences, and interpretation may be biased towards species whose individuals were initially larger. In addition, measurements at several times are necessary to understand the changing dynamics of species interaction. 5 Simple pair-wise mixtures can assess the effect of treatment factors on the outcome of competition. Replacement series and related diallel designs generally produce results that may be size-biased even when initial interspecific differences are known. Additive designs (including target{\textendash}neighbour designs), despite confounding density with species proportions, offer considerable scope for addressing mechanistic questions about interspecific interactions. Designs that allow response surface analysis can avoid many of the problems inherent in the other methods, but all need to be adjusted for initial interspecific differences. Designs for multiple species experiments are still largely untested, although several designs have been used. At the level of the individual plant, hexagonal fan designs permit study of the effects of varying the spatial pattern, and the densities and the relative proportions of interacting species, but suffer from lack of independence and lack of randomization.}, keywords = {LTER-KNZ}, doi = {10.1046/j.1365-2745.1999.00321.x}, author = {D.J. Gibson and Connolly, J. and D.C. Hartnett and Weidenhamer, J.D.} } @article {KNZ00685, title = {The Effects of fire, mowing, and fertilizer amendments on arbuscular mycorrhizas in tallgrass prairie}, journal = {American Midland Naturalist}, volume = {142}, year = {1999}, pages = {55 -69}, abstract = {Tallgrass prairie sites subjected to 10 y of annual burning, mowing, nitrogen (N) fertilization or phosphorus (P) fertilization and untreated reference sites were studied to examine effects of these management practices on arbuscular mycorrhizal (AM) symbiosis. Spring burning of native prairie field plots significantly reduced AM fungal species diversity, while increasing spore abundance. This increase in total spore number was due to a general increase in most of the 17 fungal species present. In general, the management treatments had larger effects on the richness component of diversity than on the evenness of AM species abundances. Burning and mowing had no significant effects on AM fungal colonization of roots or extraradical mycorrhizal hyphae (EMH) development. However, nitrogen fertilization significantly increased root colonization and EMH development, and P amendment decreased EMH development. There was no significant effect of fertilizer amendment on AM spore abundance, fungal species diversity or richness, but N and P fertilization decreased fungal species evenness. Effects of management practices on AM fungi may be mediated through changes in soil resources or microclimate or through changes in their host plants. These effects on AM symbiosis and community structure are important because AM fungi strongly influence the growth, demography, competitive relationships, relative abundances and diversity of plants in grassland communities.}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.1674/0003-0031(1999)142[0055:TEOFMA]2.0.CO;2}, author = {Eom, A.H. and D.C. Hartnett and G.T. Wilson and Figge, D.A.} } @article {KNZ00709, title = {Interacting influence of mycorrhizal symbiosis and competition on plant diversity in tallgrass prairie}, journal = {Oecologia}, volume = {121}, year = {1999}, pages = {574 -582}, abstract = {In tallgrass prairie, plant species interactions regulated by their associated mycorrhizal fungi may be important forces that influence species coexistence and community structure; however, the mechanisms and magnitude of these interactions remain unknown. The objective of this study was to determine how interspecific competition, mycorrhizal symbiosis, and their interactions influence plant community structure. We conducted a factorial experiment, which incorporated manipulations of abundance of dominant competitors, Andropogon gerardii and Sorghastrum nutans, and suppression of mycorrhizal symbiosis using the fungicide benomyl under two fire regimes (annual and 4-year burn intervals). Removal of the two dominant C4 grass species altered the community structure, increased plant species richness, diversity, and evenness, and increased abundance of subdominant graminoid and forb species. Suppression of mycorrhizal fungi resulted in smaller shifts in community structure, although plant species richness and diversity increased. Responses of individual plant species were associated with their degree of mycorrhizal responsiveness: highly mycorrhizal responsive species decreased in abundance and less mycorrhizal responsive species increased in abundance. The combination of dominant-grass removal and mycorrhizal suppression treatments interacted to increase synergistically the abundance of several species, indicating that both processes influence species interactions and community organization in tallgrass prairie. These results provide evidence that mycorrhizal fungi affect plant communities indirectly by influencing the pattern and strength of plant competitive interactions. Burning strongly influenced the outcome of these interactions, which suggests that plant species diversity in tallgrass prairie is influenced by a complex array of interacting processes, including both competition and mycorrhizal symbiosis.}, keywords = {LTER-KNZ, Arbuscular mycorrhizal fungi, Competition, diversity, Species coexistence, tallgrass prairie}, doi = {10.1007/s004420050964}, author = {M.D. Smith and D.C. Hartnett and G.T. Wilson} } @article {KNZ00697, title = {The keystone role of bison in North American tallgrass prairie}, journal = {BioScience}, volume = {49}, year = {1999}, pages = {39 -50}, keywords = {LTER-KNZ}, url = {http://www.jstor.org/stable/10.1525/bisi.1999.49.1.39}, author = {Alan K. Knapp and John M. Blair and J. M. Briggs and Scott. L. Collins and D.C. Hartnett and Johnson, L.C. and Towne, E.G.} } @article {KNZ00692, title = {Mycorrhizae influence plant community structure and diversity in tallgrass prairie}, journal = {Ecology}, volume = {80}, year = {1999}, pages = {1187 -1195}, abstract = {In grassland ecosystems, symbiotic associations between plants and mycorrhizal fungi are widespread and have important influences on the life histories, demography, and species interactions of plants, and on belowground ecosystem processes. To assess the consequences of the symbiosis at the plant community level, we conducted a 5-yr field experiment in tallgrass prairie to investigate the influence of arbuscular mycorrhizal fungi on plant species composition, relative abundances, and diversity. Replicate plots in which mycorrhizal fungi were suppressed with benomyl application every two weeks during each growing season, were compared to nontreated mycorrhizal control plots on six watershed units at the Konza Prairie in northeastern Kansas. Benomyl successfully reduced mycorrhizal colonization to <25\% of mycorrhizal control plots. Mycorrhizal colonization of roots in control plots was inversely related to annual precipitation. Suppression of mycorrhizae resulted in decreases in abundances of the dominant, obligately mycotrophic C4 tall grasses, compensatory increases in abundances of many subordinate facultatively mycotrophic C3 grasses and forbs, but no change in total aboveground biomass, as estimated from canopy density. Suppression of mycorrhizal symbiosis resulted in a large increase in plant species diversity. Two possible mechanisms for mycorrhizal mediation of plant species composition and diversity are: (1) alterations in resource distribution among neighbors via hyphal connections, and (2) differential host species responses to mycorrhizal fungal colonization in communities in which the competitive dominants are more strongly or more weakly mycotrophic than their neighbors. The results of this study demonstrate that mycorrhizal symbiosis can have large effects on plant community structure, and that differential host species response to fungal colonization is a key factor explaining the dominance of warm-season C4 grasses in tallgrass prairie and limiting plant species evenness and diversity. The results also underscore the importance of above- and belowground linkages in tallgrass prairie and indicate that alterations in belowground fungi and rhizosphere processes can have large effects on aboveground floristic composition and diversity in grasslands.}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.1890/0012-9658(1999)080[1187:MIPCSA]2.0.CO;2}, author = {D.C. Hartnett and G.T. Wilson} } @inbook {KNZ00649, title = {Animal populations and communities}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {113 -139}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {D.W. Kaufman and Kaufman, G.A. and Fay, P.A. and Zimmerman, J.L. and Evans, E.W.}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00661, title = {Belowground biology and processes}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {244 -264}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {C. W. Rice and Todd, T.C. and John M. Blair and Seastedt, T.R. and Ramundo, R.A. and G.T. Wilson}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00665, title = {Climate change, elevated CO2 and predictive modeling: Past and future climate change scenarios for the tallgrass prairie}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {283 -300}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, url = {http://www.colostate.edu/Depts/GDPE/Distinguished_Ecologists/2005/Hayden/grassland\%20dynamics\%20ch16.pdf}, author = {Seastedt, T.R. and Hayden, B.P. and Owensby, C.E. and Alan K. Knapp}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00633, title = {Disturbance, diversity and species interactions in tallgrass prairie}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {140 -156}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Scott. L. Collins and Steinauer, E.M.}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00648, title = {Diversity of terrestrial macrofauna}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {101 -112}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {D.W. Kaufman and Fay, P.A. and Kaufman, G.A. and Zimmerman, J.L.}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00632, title = {The dynamic tallgrass prairie: Synthesis and research opportunities}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {301 -315}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Scott. L. Collins and Alan K. Knapp and D.C. Hartnett and J. M. Briggs}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00639, title = {The flora of Konza Prairie: A historical review and contemporary patterns}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {69 -80}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Freeman, C.C.}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00657, title = {Geomorphology of the Konza Prairie}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {35 -47}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Oviatt, C.G.}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @book {KNZ001010, title = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {364 -364}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00652, title = {Grasslands, Konza Prairie and long-term ecological Research}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {3 -15}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Alan K. Knapp and Seastedt, T.R.}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00642, title = {Hydrology and aquatic chemistry}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {159 -176}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Gray, L.J. and G. L. Macpherson and Koelliker, J.K. and W. K. Dodds}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @article {KNZ00669, title = {Interspecific variation in plant responses to mycorrhizal colonization in prairie grasses and forbs}, journal = {American Journal of Botany}, volume = {85}, year = {1998}, pages = {1732 -1738}, keywords = {LTER-KNZ}, author = {G.T. Wilson and D.C. Hartnett} } @inbook {KNZ00626, title = {A landscape perspective of patterns and processes in tallgrass prairie}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {265 -279}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {J. M. Briggs and Nellis, M.D. and Turner, C.L. and Henebry, G.M. and Su, H.}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00651, title = {Patterns and controls of aboveground net primary production in tallgrass prairie}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {193 -221}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Alan K. Knapp and J. M. Briggs and John M. Blair and Turner, C.L.}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00645, title = {Plant populations: Patterns and processes}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {81 -100}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {D.C. Hartnett and Fay, P.A.}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00646, title = {Regional climate and the distribution of tallgrass prairie}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {19 -34}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, url = {http://www.colostate.edu/Depts/GDPE/Distinguished_Ecologists/2005/Hayden/grassland\%20dynamics\%20ch2.pdf}, author = {Hayden, B.P.}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00660, title = {Soils and soil biota}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {48 -66}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Ransom, M.D. and C. W. Rice and Todd, T.C. and Wehmueller, W.A.}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00643, title = {Structure and dynamics of aquatic communities}, booktitle = {Grassland Dynamics: Long-Term Ecological Research in Tallgrass Prairie}, year = {1998}, pages = {177 -189}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Gray, L.J. and W. K. Dodds}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00620, title = {Terrestrial nutrient cycling in tallgrass prairie}, booktitle = {Grassland Dynamics: Long-term Ecological Research}, year = {1998}, pages = {222 -243}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {New York}, keywords = {LTER-KNZ, tallgrass prairie}, author = {John M. Blair and Seastedt, T.R. and C. W. Rice and Ramundo, R.A.}, editor = {Alan K. Knapp and J. M. Briggs and D.C. Hartnett and Scott. L. Collins} } @inbook {KNZ00591, title = {Comparative ecology of native and introduced ungulates}, booktitle = {Ecology and Conservation of Great Plains Vertebrates}, year = {1997}, pages = {72 -101}, publisher = {Springer-Verlag}, organization = {Springer-Verlag}, address = {New York}, abstract = {The defining period of coevolution among Great Plains plant and ungulate species occurred during the past 12,000 years (Mack and Thompson 1982, Axelrod 1985). In the late Pleistocene and early Holocene, a diverse array of large grazers and browsers were reduced to a much smaller group of ungulate species represented by bison (Bison bison), pronghorn (Antilocapra americana), deer (Odocoileus hemionus and O. virginianus), and elk (Cervus canadensis). These changes occurred in the presence of nomadic humans from the Asian steppe who were immigrating to the Great Plains during the same time. The landscape was characterized by gently rolling interfluvial surfaces covered with perennial herbaceous vegetation. These exposed grasslands were periodically interrupted by more protected wetland, riparian woodland, or scarp woodland habitats. Although wetlands and woodlands occupied less than 7 and less than 3\% of the Great Plains, respectively (National Wetlands Inventory, and Nebraska Natural Heritage Program data bases), the heterogeneity that they created at landscape scales played a major role in determining the distribution and abundance of native ungulates. Extreme cold and heat, drought, flood, fire, wind, and countless biotic interactions caused locally short-term fluctuations in ungulate populations and long-term shifts in landscape features. These dynamic temporal changes were overlayed on a multi-scale spatial mosaic. Native ungulates were adapted to this landscape.}, keywords = {LTER-KNZ}, doi = {10.1007/978-1-4757-2703-6_4}, author = {D.C. Hartnett and Steuter, A.A. and Hickman, K.R.}, editor = {Knopf, F.L. and Samson, F.B.} } @article {KNZ00584, title = {Effects of bison and cattle on growth, reproduction, and abundances of five tallgrass prairie forbs}, journal = {American Journal of Botany}, volume = {84}, year = {1997}, pages = {1719 -1728}, abstract = {Forb populations were sampled on Kansas tallgrass prairie to examine the effects of native (bison) and domestic (cattle) ungulates on plant growth, reproduction, and species abundances. Five locally and regionally abundant native tallgrass prairie perennials, Baptisia bracteata, Oenothera speciosa, Vernonia baldwinii, Solidago missouriensis, and Salvia azurea, were selected for study. Replicate watershed-level treatments included three grazing regimes (ungrazed, grazed by cattle, and grazed by bison), and two spring fire frequencies (annually burned and burned at 4-yr intervals). The results show that forb responses to ungulates in tallgrass prairie are complex and vary significantly among plant species, ungulate species, fire regimes, and plant life history stages. Some forbs (e.g., B. bracteata, O. speciosa, and V. baldwinii) increased in growth and reproduction in grazed sites, indicating competitive release in response to selective grazing of the dominant warm-season matrix grasses. Forbs that reduced performance in grazed sites are likely negatively affected by disturbances generated by ungulate nongrazing activities, because none of the forbs studied were directly consumed by bison or cattle. Large grazers had no detectable effect on the frequency of plant damage by other herbivores or pathogens. Significant effects of grazers on patterns of flowering and seed production were not congruent with their effects on population densities, indicating that variation in sexual reproduction plays a minor role in regulating local population abundances. Furthermore, the native and domestic ungulates differ significantly in their effects on forb growth and reproduction.}, keywords = {LTER-KNZ, tallgrass prairie}, url = {http://www.amjbot.org/content/84/12/1719.short}, author = {Damhoureyeh, S.A. and D.C. Hartnett} } @article {KNZ00616, title = {Effects of mycorrhizae on plant productivity and species abundances in tallgrass prairie microcosms}, journal = {American Journal of Botany}, volume = {84}, year = {1997}, pages = {478 -482}, abstract = {Experimental microcosms (40 X 52 X 32 cm) containing an assemblage of eight tallgrass prairie grass and forb species in native prairie soil were maintained under mycorrhizal (untreated control) or mycorrhizal-suppressed (fungicide-treated) conditions to examine plant growth, demographic, and community responses to mycorrhizal symbiosis. The fungicide benomyl successfully reduced mycorrhizal root colonization in the fungicide-treated microcosms to only 6.4\% (an 83\% reduction relative to mycorrhizal controls). Suppression of mycorrhizas resulted in a 31\% reduction in total net aboveground plant production and changes in the relative production of C4 and C3 plants. The C4 tallgrasses Andropogon gerardi and Sorghastrum nutans produced less plant biomass in the fungicide-treated microcosms, and had a greater ratio of reproductive to vegetative biomass. Cool-season C3 grasses, Koeleria pyramidata and Poa pratensis accumulated more biomass and were a significantly greater proportion of total community biomass in mycorrhizal-suppressed microcosms. Forbs showed variable responses to mycorrhizal suppression. The two legumes Amorpha canescens and Dalea purpurea had significantly lower survivorship in the fungicide-treated microcosms, relative to the controls. The results confirm the high mycorrhizal dependency and growth responsiveness of dominant prairie grasses, and indicate that differential growth and demographic responses to mycorrhizal colonization among species may significantly affect plant productivity and species relative abundances in tallgrass prairie}, keywords = {LTER-KNZ, tallgrass prairie}, url = {http://www.ncbi.nlm.nih.gov/pubmed/21708601}, author = {G.T. Wilson and D.C. Hartnett} } @article {KNZ00547, title = {Effects of bison grazing, fire and topography on floristic diversity in tallgrass prairie}, journal = {Journal of Range Management}, volume = {49}, year = {1996}, pages = {413 -420}, abstract = {Grazed and ungrazed sites subjected to different fire frequencies were sampled on the Konza Prairie Research Natural Area in northeast Kansas after 4 years of bison grazing (1987-1991). The objective was to study effects of bison grazing on plant species composition and diversity components (plant species richness, equitability, and spatial heterogeneity) in sites of contrasting fire frequency. Cover and frequency of cool-season graminoids (e.g. Poa pratensis L., Agropyron smithii Rydb., Carex spp.) and some forbs (e.g. Aster ericoides [A. Gray] Howell, and Oxalis stricta L.) were consistently higher in sites grazed by bison than in ungrazed exclosures, whereas the dominant warm-season grasses (Andropogon gerardii Vitman, Sorghastrum nutans [L.] Nash, Panicum virgatum L., Schizachyrium scoparium [Michx.] Nash) and other forbs (e.g. Solidago missouriensis Nutt.) decreased in response to bison. Plant species diversity (H') and spatial heterogeneity in all areas sampled were significantly increased by bison. Increased heterogeneity and mean species richness in grazed prairie (40 species per sample site) compared to ungrazed prairie (29 species per site) were likely a result of greater microsite diversity generated by bison, whereas preferential grazing of the dominant grasses and concomitant increases in subordinate species resulted in an increase in equitability of species abundances. Species/area relationships indicated greater effects of bison on plant species richness with increasing sample area. Increases in plant diversity components associated with bison grazing were generally greater in annually burned than in 4-year burned sites. Effects of ungulate grazers on floristic diversity have important implications given recent evidence that plant species diversity and the compositional and production stability of grassland plant communities are positively related.}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.2307/4002922}, author = {D.C. Hartnett and Hickman, K.R. and Walter, L.E.F.} } @proceedings {KNZ00548, title = {Effects of bison grazing on plant species diversity in tallgrass prairie}, year = {1996}, pages = {215 -216}, keywords = {LTER-KNZ, tallgrass prairie}, author = {D.C. Hartnett and Hickman, K.R. and Walter, L.E.F.}, editor = {West, N.E.} } @proceedings {KNZ00551, title = {Effects of grazing systems and stocking rates on plant species diversity in Kansas tallgrass prairie}, year = {1996}, pages = {228 -229}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Hickman, K.R. and D.C. Hartnett and Cochran, R.C.}, editor = {West, N.E.} } @article {KNZ00541, title = {Interspecific nutrient transfer in a tallgrass prairie plant community}, journal = {American Journal of Botany}, volume = {83}, year = {1996}, pages = {180 -184}, abstract = {Interplant nutrient transfer may be an important ecological process in grasslands, and may significantly influence plant neighborhood interactions. We investigated the potential for phosphorus transfer between the dominant grass Andropogon gerardii and several neighboring plant species in tallgrass prairie via a field 32PO4 labelling experiment. The mean amount of 32P received from donor shoots differed significantly among neighboring species and decreased with increasing distance from the donor. In general, forbs and cool-season C3 grasses received more labelled 32P than warm-season C4 grasses. Phosphorus transfer occurred over distances up to 0.5 m. The effects of species and distance on movement of phosphorus changed with increasing time after labelling. The relative mass of receiver and donor shoots did not affect amounts of 32P transfer. A benomyl fungicide treatment, applied to suppress mycorrhizal activity, likely did not affect existing vegetative hyphae and did not affect the amount of 32P transferred. These studies demonstrate that: (1) phosphorus is transferred among neighboring species in tallgrass prairie plant communities, (2) phosphorus may be transferred over significantly greater distances than reported in other grasslands, and (3) there is differential transfer among co-occurring species. Hypothesized mechanisms accounting for these patterns in tallgrass prairie include mycorrhizal hyphal interconnections and/or extensive and differential root and rhizosphere overlap among neighboring species.}, keywords = {LTER-KNZ, mycorrhizae, Phosphorus, tallgrass prairie}, url = {http://www.jstor.org/stable/2445936}, author = {Walter, L.E.F. and D.C. Hartnett and Hetrick, B.A.D. and Schwab, A.P.} } @article {KNZ00540, title = {Plant tolerance of gall-insect attack and gall-insect performance}, journal = {Ecology}, volume = {77}, year = {1996}, pages = {521 -534}, abstract = {We examined plant tolerance of gall{\textemdash}insect attack and gall{\textemdash}insect performance in rosinweed (Silphium integrifolium, Asteraceae) and its apical meristem galler Antistrophus silphii (Hymenoptera: Cynipidae). Gall densities were varied in field rosinweed populations, while gall densities, water, and nutrients were varied for rosinweed in an experimental garden. Field plants grew under prevailing resource and competitive conditions, but garden plants grew free from competition, so gall{\textemdash}insect impacts, rosinweed regrowth, and gall{\textemdash}insect performance were observed under widely different growing conditions. Seasonal measures of rosinweed growth and leaf physiology, and end{\textemdash}of{\textemdash}season measures of biomass, reproduction, gall{\textemdash}wasp emergence, growth, sex ratios, and parasitism were made for both experiments. Rosinweed poorly tolerated Antistrophus gall damage in the field. Galls reduced plant height, leaf area, and inflorescence production. Rosinweed diverted biomass to stems, but produced no regrowth from axillary meristems. In the garden, rosinweed was much more tolerant of Antistrophus gall damage. Galls initially reduced plant height and leaf area, but axillary meristems grew profusely after gall formation, producing nearly all galled plant inflorescences and more than replacing leaf area initially lost to gall formation. Water{\textemdash} and nutrient{\textemdash}supplemented rosinweed were most tolerant of gall damage, experiencing little loss of total biomass or reproductive output. Field rosinweed failed to mount a tolerance{\textemdash}enhancing regrowth response because galls, resource availability, and competition combined to constrain axillary meristem growth. Gall{\textemdash}wasp performance was largely independent of rosinweed tolerance. Emergence, growth, sex ratios, and parasitism were comparable in field and garden, and only slightly affected by resource availability. Gall{\textemdash}insect performance may be buffered from environmental variation, disconnecting plant and herbivore population dynamics. Rosinweed{\textquoteright}s poor tolerance of gall damage may typify forb responses to herbivory in highly competitive grassland plant communities.}, keywords = {LTER-KNZ}, doi = {10.2307/2265627}, author = {Fay, P.A. and D.C. Hartnett and Alan K. Knapp} } @article {KNZ00511, title = {Bison selectivity and grazing responses of little bluestem in tallgrass prairie}, journal = {Journal of Range Management}, volume = {48}, year = {1995}, pages = {26 -31}, abstract = {The perennial bunchgrass little bluestem (Schizachyrium scoparium [Michx.] Nash) was examined in a 5-yr study on tallgrass prairie to determine how fire influences its use by bison and its responses to grazing. On unburned prairie, bison grazed only 5\% of the available little bluestem, selecting it only 30\% as frequently as big bluestem, the dominant co-occurring species. On burned prairie, grazing frequency of little bluestem was over 3-fold greater and equal to that of its dominant neighbor. Grazing frequency of little bluestem was affected by plant size (basal area). On burned sites, plants of intermediate size classes were least abundant (<10\% of total) but were grazed most frequently (>50\%). Small plants were most abundant but were grazed least frequently. Density, tiller numbers, and basal area of little bluestem were significantly greater in annually burned compared to infrequently burned sites but were decreased by > 50\% in grazed compared to ungrazed sites. Grazing shifted the population size distribution toward higher frequencies of smaller individuals (< 50 cm2 basal area), whereas burning increased the frequency of large (> 200 cm2 basal area) individuals. In unburned prairie, little bluestem accumulates a persistent clump of standing dead tillers that appear to serve as a physical deterrent to grazing. Although burning enhances its growth, it also removes its canopy of dead tillers exposing the plant to grazers. The shift in population structure toward a high frequency of smaller (and perhaps less drought- or grazing-tolerant) individuals may contribute to the decline of little bluestem populations under persistent grazing. Thus, plant growth form, population size structure, and fire interact to influence bison grazing patterns and responses of little bluestem to grazing on tallgrass prairie.}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.2307/4002500}, author = {Pfeiffer, K.E. and D.C. Hartnett} } @proceedings {KNZ00487, title = {Dynamics of big bluestem (Andropogon gerardii) in ungrazed tallgrass prairie}, year = {1995}, pages = {9 -15}, keywords = {LTER-KNZ}, author = {D.J. Gibson and Towne, E.G.}, editor = {D.C. Hartnett} } @proceedings {KNZ00506, title = {Effect of topography on the distribution of small mammals on the Konza Prairie Research Natural Area, Kansas}, year = {1995}, pages = {97 -102}, keywords = {LTER-KNZ}, url = {http://images.library.wisc.edu/EcoNatRes/EFacs/NAPC/NAPC14/reference/econatres.napc14.gkaufman.pdf}, author = {Kaufman, G.K. and D.W. Kaufman and Brillhart, D.E. and Finck, E.J.}, editor = {D.C. Hartnett} } @proceedings {KNZ00493, title = {Effects of bison grazing, on floristic diversity in tallgrass prairie}, year = {1995}, pages = {215 -216}, keywords = {LTER-KNZ, tallgrass prairie}, author = {D.C. Hartnett and Hickman, K.R. and Walter, L.E.F.} } @proceedings {KNZ00490, title = {Environmental and physiological factors influencing the distribution of oaks near the edge of their range}, year = {1995}, pages = {17 -20}, keywords = {LTER-KNZ}, url = {http://images.library.wisc.edu/EcoNatRes/EFacs/NAPC/NAPC14/reference/econatres.napc14.ehamerlynck.pdf}, author = {Hamerlynck, E.P. and Alan K. Knapp}, editor = {D.C. Hartnett} } @proceedings {KNZ00501, title = {Gas exchange and reproduction of Spiranthes vernalis (Orchidaceae) in a Kansas tallgrass prairie}, year = {1995}, pages = {21 -24}, keywords = {LTER-KNZ, tallgrass prairie}, url = {http://images.library.wisc.edu/EcoNatRes/EFacs/NAPC/NAPC14/reference/econatres.napc14.sjohnson.pdf}, author = {Johnson, S.R.}, editor = {D.C. Hartnett} } @proceedings {KNZ00514, title = {The influence of crowding and pocket gopher disturbance on growth and reproduction of a biennial, Tragopogon dubius}, year = {1995}, pages = {123 -127}, keywords = {LTER-KNZ}, url = {http://images.library.wisc.edu/EcoNatRes/EFacs/NAPC/NAPC14/reference/econatres.napc14.oreichman.pdf}, author = {Reichman, O.J.}, editor = {D.C. Hartnett} } @proceedings {KNZ00521, title = {Influence of fire frequency and burning date on the proportion of reproductive tillers in big bluestem and indiangrass}, year = {1995}, pages = {75 -78}, keywords = {LTER-KNZ, fire}, url = {http://images.library.wisc.edu/EcoNatRes/EFacs/NAPC/NAPC14/reference/econatres.napc14.etowne.pdf}, author = {Towne, E.G.}, editor = {D.C. Hartnett} } @proceedings {KNZ00496, title = {Observing spatial structure in the Flint Hills using AVHRR biweekly composites of maximum NDVI}, year = {1995}, pages = {143 -151}, keywords = {LTER-KNZ}, author = {Henebry, G.M. and Su, H.}, editor = {D.C. Hartnett} } @proceedings {KNZ00480, title = {Population ecology of Elliot{\textquoteright}s short-tail shrew and least shrew in ungrazed tallgrass prairie}, year = {1995}, pages = {87 -92}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Clark, B.K. and D.W. Kaufman and Kaufman, G.A. and Gurtz, S.K.}, editor = {D.C. Hartnett} } @inbook {KNZ00492, title = {Population Processes}, booktitle = {The Changing Prairie}, year = {1995}, pages = {82 -99}, publisher = {Oxford University Press}, organization = {Oxford University Press}, address = {Oxford}, keywords = {LTER-KNZ}, author = {D.C. Hartnett and Keeler, K.H.}, editor = {Anthony Joern and Keeler, K.K.} } @proceedings {KNZ00505, title = {Prairie voles impact plants in tallgrass prairie}, year = {1995}, pages = {117 -121}, keywords = {LTER-KNZ, tallgrass prairie}, author = {D.W. Kaufman and Bixler, S.H.}, editor = {D.C. Hartnett} } @proceedings {KNZ00479, title = {Small-mammal use of experimental patches of tallgrass prairie: influence of topographic position and fire history}, year = {1995}, pages = {59 -65}, keywords = {LTER-KNZ, tallgrass prairie}, author = {Brillhart, D.E. and Kaufman, G.A. and D.W. Kaufman}, editor = {D.C. Hartnett} } @proceedings {KNZ00524, title = {Wetlands may change tallgrass prairie from a sink to a source for atmospheric methane}, year = {1995}, pages = {137 -141}, keywords = {LTER-KNZ, tallgrass prairie}, url = {http://images.library.wisc.edu/EcoNatRes/EFacs/NAPC/NAPC14/reference/econatres.napc14.jyavitt.pdf}, author = {Yavitt, J.B. and Alan K. Knapp}, editor = {D.C. Hartnett} } @article {KNZ00447, title = {Effects of mycorrhizal and plant density on yield relationships among competing tallgrass prairie grasses}, journal = {Canadian Journal of Botany}, volume = {72}, year = {1994}, pages = {168 -176}, abstract = {A replacement series experiment was used to investigate the effects of mycorrhizae, phosphorus availability, and plant density on competitive relationships between three tallgrass prairie species of varying mycorrhizal dependencies. Under mycorrhizal conditions, the obligately mycorrhizal dependent warm-season grass Andropogon gerardii (big bluestem) was a better competitor in mixture with the nonmycorrhiza-dependent cool-season grass Koeleria pyramidata (Junegrass). In the absence of mycorrhizae, however, competitive effects of big bluestem were greatly reduced and Junegrass experienced competitive release. Relative yield totals increased when mycorrhizae were suppressed, suggesting greater intensity of interspecific competition in the presence of mycorrhizae. Thus, the competitive dominance of big bluestem in tallgrass prairie is strongly related to its mycorrhizal status. Elymus canadensis (Canada wild rye) outcompeted big bluestem both with and without mycorrhizae. Relative yield totals of this species mixture were also lower under mycorrhizal conditions, indicating that mycorrhizae increase the intensity of interspecific competition between them. Relative yields of wild rye competing with big bluestem increased in the absence of mycorrhizae, suggesting that it also experiences competitive release when big blue-stem are not mycorrhizal. The outcomes of competition were generally similar among the three total plant density treatments and between P-fertilized and nonfertilized treatments. However, interactions between mycorrhizal effects and plant density confirm that outcomes of interspecific competitive interactions may be density dependent in some cases.}, keywords = {LTER-KNZ, Andropogon gerardii, arbuscular mycorrhizae, de Wit replacement series, Elymus canadensis, Koeleria pyramidata}, doi = {10.1139/b94-023}, author = {Hetrick, B.A.D. and D.C. Hartnett and G.T. Wilson and D.J. Gibson} } @article {KNZ00445, title = {Plant demographic responses to mycorrhizal symbiosis in tallgrass prairie}, journal = {Oecologia}, volume = {99}, year = {1994}, pages = {21 -26}, abstract = {The effects of mycorrhizal symbiosis on seedling emergence, flowering and densities of several grasses and forbs were assessed in native tallgrass prairie and in sown garden populations at the Konza Prairie in northeastern Kansas. Mycorrhizal activity was experimentally suppressed with the fungicide benomyl. Flowering and stem densities of the cool-season grass, Dichanthelium oligosanthes, sedges (Carex spp.), and the forb Aster ericoides were higher in non-mycorrhizal (benomyl-treated) than in mycorrhizal plots and the magnitude of these differences was significantly affected by burning. Mycorrhizae significantly enhanced flowering of the warmseason grasses Andropogon gerardii and Sorghastrum nutans in burned prairie, but not in unburned sites. These patterns suggest that mycorrhizal effects on the dynamics of cool-season graminoid and forb populations are likely to be mediated indirectly through effects of the symbiosis on the competitive dominance of their neighbors. Seedling emergence rates of the cool-season C3 grasses Elymus canadensis and Koeleria cristata were significantly reduced in the benomyl-treated plots, whereas benomyl treatment had no significant effect on seedling emergence of the warm-season C4 grasses A. gerardii and Panicum virgatum. The forbs showed variable responses. Seedling emergence of Liatris aspera was greater under mycorrhizal conditions, but that of Dalea purpurea was unaffected by mycorrhizal treatment. These results show that effects of mycorrhizal symbiosis on the population dynamics of co-occurring prairie plants vary significantly both among species and among different life history stages within species. The results also indicate that mycorrhizas and fire interact to influence competitive interactions and demographic patterns of tallgrass prairie plant populations.}, keywords = {LTER-KNZ, fire, tallgrass prairie, VA mycorrhizas Plant demography}, doi = {10.1007/BF00317079}, author = {D.C. Hartnett and Samenus, R.H. and Fischer, L.E. and Hetrick, B.A.D.} } @article {KNZ00399, title = {Increased photosynthesis and water potentials in Silphium integrifolium galled by cynipid wasps}, journal = {Oecologia}, volume = {93}, year = {1993}, pages = {114 -120}, abstract = {Interactions between drought, insect herbivory, photosynthesis, and water potential play a key role in determining how plants tolerate and defend against herbivory, yet the effects of insect herbivores on photosynthesis and water potential are seldom assessed. We present evidence that cynipid wasp galls formed by Antistrophus silphii on Silphium integrifolium increase photosynthesis (A), stomatal conductance (g), and xylem water potential (Ψ). Preliminary data showed that in drought-stressed plants galled shoots had 36\% greater A, and 10\% greater stem Ψ than ungalled shoots, while in well-watered plants leaf gas exchange was not affected by galls. We hypothesized that 1) galled shoots have higher Ψ, g, and A than ungalled shoots, but this differences diminishes if plant drought stress is reduced, and 2) galls can reduce decreases in A and g if water availability decreases. A field experiment testing the first hypothesis found that galls increased g and Ψ, but that differences between galled and ungalled shoots did not diminish after plants were heavily watered. A laboratory test of the second hypothesis using potted Silphium found that galled plants had smaller drops in A and g over a 4-day dry-down period. A vs g and A vs intercellular CO2 concentration relationships were consistent with the explanation that increased Ψ allows galls to increase A by reducing stomatal limitation of A, rather than by altering sink-source relationships or by removing low-Ψ limitations on non-stomatal components of A. Our working hypothesis is that galls increase Ψ and A by reducing the shoot: root ratio so that the plant is exploiting a greater soil volume per unit leaf area. We argue that increased A is an ineffective way for Silphium to compensate for negative effects of gall insect attack. Instead, increased Ψ and A may protect gall insects from variation in resource availability caused by periodic drought stress, potentially reducing negative effects of drought on plant quality and on gall insect populations.}, keywords = {LTER-KNZ, Gall insect, photosynthesis, Plant-insect interactions, Silphium integrifolium, Water potential}, doi = {10.1007/BF00321200}, author = {Fay, P.A. and D.C. Hartnett and Alan K. Knapp} } @article {KNZ00430, title = {The interactive effects of fire, bison (Bison bison) grazing and plant community composition in tallgrass prairie}, journal = {American Midland Naturalist}, volume = {129}, year = {1993}, pages = {10 -18}, abstract = {Fire and native large herbivore grazing were two important influences on the structure and function of North American grasslands. In 1988 and 1989 the influence of fire regime on grazing patterns of North American bison (Bison bison) was studied on the Konza Prairie in northeastern Kansas. Bison grazing was spatially and temporally nonrandom and was influenced by fire regime and local plant community composition. During the growing season, bison were observed up to 3 x more frequently than expected on watersheds burned in the spring. Summer grazing was concentrated in large watershed areas (79-119 ha) dominated by warm-season, perennial, C4 grasses. During the autumn and winter, bison grazed both burned and unburned watersheds more uniformly but grazed most intensively in areas with large stands of cool-season, C3 grasses. On a smaller spatial scale (5-10 m2), bison selected patches during the growing season with low forb cover dominated by the perennial C4 grass, Andropogon gerardii. Grazed patches were larger on frequently burned than on infrequently burned watersheds. The importance of fire history in determining patterns of bison grazing over the landscape indicates that interactions between bison grazing and fire regime may be important to the composition and spatial heterogeneity of tallgrass prairie vegetation.}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.2307/2426430}, author = {Vinton, M.A. and D.C. Hartnett and Finck, E.J. and J. M. Briggs} } @article {KNZ00404, title = {Regulation of clonal growth and dynamics of Panicum virgatum in tallgrass prairie: effects of neighbor removal and nutrient addition}, journal = {American Journal of Botany}, volume = {80}, year = {1993}, pages = {1114 -1120}, abstract = {Clones of the perennial grass Panicum virgatum were studied on the Konza Prairie in northeast Kansas to determine the effects of neighbors, nutrient availability, and physiological integration on ramet population dynamics and clonal growth and architecture. Opposite halves of established clones in the field were subjected differentially to treatments including neighbor removal and nitrogen addition, with intact or severed rhizome connections between halves. Neighborhood competition strongly influenced clone architecture and expansion rates. Removal of neighbors resulted in a >95\% increase in radial clone expansion, intraclonal ramet densities, ramet population growth rates, ramet biomass, and percent of stems flowering, averaged over a 4-year period relative to halves or clones with intact competitors. Plant responses suggest that effects of interclonal neighbors are mediated through alteration of the light environment in the clone canopy and water availability. Addition of nitrogen did not affect lateral spread or clone structure, but resulted in significant increases in ramet size, flowering, and seed production. ANOVA revealed no significant effect of rhizome severing or treatment x severing interactions, suggesting that the size of the integrated physiological unit is much smaller than clone size and/or that physiological integration had no effect on clone responses to environmental heterogeneity at the scale of the diameter of established clones.}, keywords = {LTER-KNZ, tallgrass prairie}, url = {http://www.jstor.org/stable/2445538}, author = {D.C. Hartnett} } @article {KNZ00405, title = {VA-Mycorrhizal influence on intra- and interspecific neighbor interactions among co-occurring prairie grasses}, journal = {Journal of Ecology}, volume = {81}, year = {1993}, pages = {787 -795}, abstract = {1 A strongly obligately mycorrhiza-dependent grass, Andropogon gerardii, and a less dependent species, Elymus canadensis, were grown in intra- and interspecific combination in a target-neighbour experiment with and without mycorrhizal fungi to examine their influence on competition. 2 Mycorrhizal fungi significantly influenced the competitive effects and responses of both plant species. Strong competitive effects of Andropogon disappeared in the absence of mycorrhizas indicating that its competitive dominance in tallgrass prairie is highly dependent upon its mycorrhizal associations. The influence of mycorrhizal fungi on Andropogon responses to neighbours decreased with increasing neighbour density indicating reduced host plant benefit from mycorrhizas under crowded conditions. 3 Effects of mycorrhizas on competition were generally smaller for the less mycorrhiza-dependent Elymus. Elymus effects on target plants were not strongly affected by mycorrhizas. Elymus target plants in competition with Andropogon neighbours performed better when nonmycorrhizal, due to the lack of significant competitive suppression by Andropogon in the absence of mycorrhizas. The influence of mycorrhizal fungi on Elymus responses to Andropogon neighbours increased with increasing neighbour density. Neither mycorrhizas nor phosphorus fertilization had a significant effect on intraspecific competition among Elymus. 4 Patterns of tiller production by target plants were similar to patterns in their total dry weight, indicating that competitive and mycorrhizal effects on target plant size were primarily a result of effects on tiller numbers rather than individual tiller size. 5 The results show that mycorrhizal symbiosis can strongly influence the patterns and intensity of both intraspecific density effects and interspecific competition between co-occurring prairie grasses and that the degree of host-plant benefit derived from mycorrhizas is density dependent.}, keywords = {LTER-KNZ}, doi = {10.2307/2261676}, author = {D.C. Hartnett and Hetrick, B.A.D. and G.T. Wilson and D.J. Gibson} } @article {KNZ00384, title = {Effects of bison grazing on Andropogon gerardii and Panicum virgatum in burned and unburned tallgrass prairie}, journal = {Oecologia}, volume = {90}, year = {1992}, pages = {374 -382}, abstract = {

Responses to clipping and bison grazing in different environmental contexts were examined in two perennial grass species, Andropogon gerardii and Panicum virgatum, on the Konza Prairie in northeastern Kansas. Grazed tillers had lower relative growth rates (RGR) than clipped tillers following defoliation but this difference was transient and final biomass was not affected by mode of defoliation. Grazed tillers of both species had higher RGR throughout the season than ungrazed tillers, resulting in exact compensation for tissue lost to defoliation. However, A. gerardii tillers which had been grazed repeatedly the previous year (1988) had reduced relative growth rates, tiller biomass and tiller survival in 1989. This suggests that the short-term increase in aboveground relative growth rates after defoliation had cost to future growth plant growth and tiller survival. In general, two species had similar responses to defoliation but their responses were altered differentially by fire. The increase in RGR following defoliation of A. gerardii was relatively greater on unburned than burned prairie, and was relatively greater on unburned than burned prairie, and was influenced by topographic position. P. virgatum responses to defoliation were similar in burned and unburned prairie. Thus grazing, fire, and topographical position all intreract to influence tiller growth dynamics and these two species respond differently to the fire and grazing pattern to influence a plants\&$\#$39; grazing history and thus its long tern performance. Key words: grazing, bison, fire, Andropogon gerardii, Panicum virgatum

}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.1007/BF00317694}, author = {Vinton, M.A. and D.C. Hartnett} } @article {KNZ00316, title = {Constraints on the growth and allocation patterns of Silphium integrifolium (Asteraceae ) caused by cynipid gall wasps}, journal = {Oecologia}, volume = {88}, year = {1991}, pages = {243 -250}, keywords = {LTER-KNZ}, doi = {10.1007/BF00320818}, author = {Fay, P.A. and D.C. Hartnett} } @article {KNZ00294, title = {Field bioassessment for selecting test systems to evaluate military training lands in tallgrass prairie}, journal = {Ecosystem Health.V.1 Environmental Management}, volume = {14}, year = {1990}, pages = {81 -93}, abstract = {

Ecosystems responses to physical or chemical stress may vary from changes in single organisms to alteration of the structure and function of the ecosystem. These responses to stress cannot be predicted exactly. Ecosystems repeatedly exposed to physical and/or chemical stress can be used to study the separate and combined environmental effects of stress. Such studies also allow the development of procedures to select test systems for the analysis of stress in ecosystems. A preliminary field survey of six military training sites at Fort Riley, Kansas, USA, was conducted to identify and verify ecological test systems for evaluating ecosystem responses to physical and/or chemical stress. Comparisons of these data with data collected concurrently from Konza Prairie Research Natural Area reference sites showed that soil microarthropods, some species of macroarthropods, small mammals, and native earthworm species were negatively affected by stress. In contrast, plant species diversity, plant foliage biomass, soil mycorrhizae, and many soil characteristics were within the boundaries of nominal variations observed on \"pristine\" Konza Prairie. Introduced European earthworms appeared to be positively affected by training activities. This study provided a test of systematic procedures to support impact analysis, ecological toxicology, and ecosystem risk assessment

}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.1007/BF02394022}, author = {Schaeffer, D.J. and Seastedt, T.R. and D.J. Gibson and D.C. Hartnett and Hetrick, B.A.D. and James, S.W. and D.W. Kaufman and Schwab, A.P. and Herricks, E.E. and Novak, E.W.} } @article {KNZ00278, title = {Fire temperature heterogeneity in contrasting fire-prone habitats: Kansas tallgrass prairie and Florida sandhills}, journal = {Bulletin of the Torrey Botanical Club}, volume = {117}, year = {1990}, pages = {349 -356}, abstract = {

Spatial patterns of fire temperatures from a tallgrass prairie and adjacent Gallery forest in northeast Kansas and a sandhill community in central Florida were recorded using temperature sensitive pyrometers. The objectives of the study were to determine, in both habitats, the range of temperatures reached during prescribed burning under a range of different conditions. Both habitats are characterized by frequent, low- intensity fires confined to the herbaceous vegetation and low shrubs. In tallgrass prairie, fire temperature maxima ranged from 19 to 399oC (n=243). The highest temperatures were associated with fires in isolated tree and shrub canopies (399oC). Fires were hotter in headfires compared with backfires (47oC difference), on lowlands compared with uplands (12oC difference), and in areas that had not been burned for many years compared with areas burned annually (34oC difference). In the Florida sandhill, fire temperature maxima ranged from 35 to 538oC (n=240), with the highest temperatures recorded at ground level in sites which had not been burned for at least 5 years. Compared with frequently burned areas, areas that have not burned for many years build up high fuel loads that support a more homogeneous, hotter fire. In the tallgrass prairie, homogeneity of fire temperatures was greatest in areas of intermediate fire frequencies. The greater spatial heterogeneity in fire characteristics of prairie with very high fire frequency (annual fire) and very low frequency (greater than 15 years between fires) is likely a result of low fuel loads and more patchy vegetation structure, respectively. In sandhill, low fuel loads and patchy distribution of fuel contribute to high spatial variability in fire temperatures in annually burned sites. Key words: fire, Florida, grassland, Kansas, sandhill, temperature

}, keywords = {LTER-KNZ, fire;gallery forest;tallgrass prairie}, doi = {10.2307/2996832}, author = {D.J. Gibson and D.C. Hartnett and Smith-Merrill, G.} } @article {KNZ00280, title = {Size-dependent allocation to seed and vegetative reproduction in four clonal composites}, journal = {Oecologia}, volume = {84}, year = {1990}, pages = {254 -259}, abstract = {

Populations of Silphium speciosum, Vernonia baldwinii, Solidago canadensis and Pityopsis graminifolia were studied to determine whether biomass allocation to sexual and vegetative reproduction and the balance between them were size-dependent and whether interpopulation differences in allocation patterns could be predicted from differences in population size distributions. All four species showed strong linear relationships between inflorescence mass and vegetative mass with negative y-intercepts. As a result, sexual reproductive effort (SRE) was a monotonically increasing function of ramet size. Genet size was a poor predictor of SRE. In each species, the regression parameters of these relationships differed significantly between burned and unburned habitats indicating size-independent interpopulation differences in patterns of reproductive effort as well as size-dependent effects. Interpopulation variation in vegetative reproductive effort (VRE) was greater than variation in SRE, but neither VRE nor the pattern of partitioning of VRE among daughter rhizomes showed significant relationships to plant size. Key words: reproductive allocation, life history, vegetative reproduction

}, keywords = {LTER-KNZ}, doi = {10.1007/BF00318281}, author = {D.C. Hartnett} } @article {KNZ00230, title = {Density and growth stage-dependent responses to defoliation in two rhizomatous grasses}, journal = {Oecologia}, volume = {80}, year = {1989}, pages = {414 -420}, abstract = {

Responses to defoliation were studied in two tallgrass prairie perennials (Andropogon gerardii and Panicum virgatum) established from seed at three densities. P. virgatum was also grown from transplanted rhizomes of established clones. Plants of both species displayed a continuum of responses to defoliation, from large reductions in biomass, tillering and seed production to significant increases in one or more performance measures. In crowded populations, defoliation shifted plants into subordinate positions within the competitive hierachy. Plants competing inrtaspecifically and those that were initally small suffered more from defoliation than either plants grown at low density or those that were larger than their neighbors. At the highest plant density, the effects of defoliation or initial plant size were overshadowed by the effects of crowding. When defoliated and grown at similar densities, P. virgatum and A. gerardii grown from seed showed large reductions in biomass, seed production, and new rhizome production, but established P. virgatum ramets grown from rhizomes showed increases in these performance measures. Thus herbivory may be particularly detrimental to P. virgatum during juvenile stages before perennating organs have developed. Overcompensation of P. virgatum clones in reaponse to defoliation only occurred if all ramets within the clone were defoliated. In clones containing both defoliated and undamaged ramets, there were no differences in their performance, suggesting that genets are capable of integrating the effects of differential defoliation among shoots. Defoliated P. virgatum clones allocated a smaller fraction of their total biomass to new rhizomes, indicating that the short-term regrowth response following defoliation may incur a longer-term cost associated with gradual reduction in biomass of the perennating organs and reduced genet success. Key words: Herbivory, Competition, Clonal growth, Panicum, Andropogon

}, keywords = {LTER-KNZ, tallgrass prairie}, doi = {10.1007/BF00379045}, author = {D.C. Hartnett} } @article {KNZ00258, title = {Density dependent phytotoxicity: distinguishing resource competition and allelopathic interference in plants}, journal = {Journal of Applied Ecology}, volume = {26}, year = {1989}, pages = {613 -624}, abstract = {

1) Experimental plant populations were grown at varying densities and varying levels of phytotoxins in the soil to investigate the potential interacting influences of allelopathy and resource competition on plant response and yield-density relationships. 2) Experiments were performed with (a) bahiagrass, Paspalum notatum, grown in soil treated with gallic acid and hydroquinone, putative inhibitors produced by Polygonella myriophylla and (b) tomato, Lycopersicon esculentum, grown in soils from under and around black walnut, Juglans nigra. 3) Phytotoxicity decreased as plant density increased. This was attributed to plant dilution of phytotoxins, i.e., the sharing of the available phytotoxin among many plants at high densities such that each received a small sub- lethal dose. 4) Phytotoxins caused characteristic deviations from expected yield-density relationships. Low to moderate phytotoxin concentrations caused a decrease in the slope of the log yield-log density relationship. Contrary to the expected consequences of increased density and resource competition, the presence of high phytotoxin concentrations may cause a reversal in the slope of predicted log yield-log density relationships at low plant densities, such that maximum individual plant weight occurs at an intermediate density. 5) Demonstration of either decreasing phytotoxicity with increasing plant density or a reversal in slope of the predicted log yield-log density relationship is proposed as an indication of the presence of toxic substances in soil. 6) The ecological implications of these results are discussed

}, keywords = {LTER-KNZ}, doi = {10.2307/2404086}, author = {Wiedenhamer, J.D. and D.C. Hartnett and Romeo, J.T.} }