02743nas a2200217   4500008004100000245008300041210006900124490000700193520201500200653000902215653003002224653002302254653002002277653002602297653002102323100001302344700001702357700001702374700001902391856011502410       2019                        eng d00aEffects of fire and large herbivores on canopy nitrogen in a tallgrass prairie0 aEffects of fire and large herbivores on canopy nitrogen in a tal0 v113 a<p>This study analyzed the spatial heterogeneity of grassland canopy nitrogen in a tallgrass prairie with different treatments of fire and ungulate grazing (long-term bison grazing vs. recent cattle grazing). Variogram analysis was applied to continuous remotely sensed canopy nitrogen images to examine the spatial variability in grassland canopies. Heterogeneity metrics (e.g., the interspersion/juxtaposition index) were calculated from the categorical canopy nitrogen maps and compared among fire and grazing treatments. Results showed that watersheds burned within one year had higher canopy nitrogen content and lower interspersions of high-nitrogen content patches than watersheds with longer fire intervals, suggesting an immediate and transient fire effect on grassland vegetation. In watersheds burned within one year, high-intensity grazing reduced vegetation density, but promoted grassland heterogeneity, as indicated by lower canopy nitrogen concentrations and greater interspersions of high-nitrogen content patches at the grazed sites than at the ungrazed sites. Variogram analyses across watersheds with different grazing histories showed that long-term bison grazing created greater spatial variability of canopy nitrogen than recent grazing by cattle. This comparison between bison and cattle is novel, as few field experiments have evaluated the role of grazing history in driving grassland heterogeneity. Our analyses extend previous research of effects from pyric herbivory on grassland heterogeneity by highlighting the role of grazing history in modulating the spatial and temporal distribution of aboveground nitrogen content in tallgrass prairie vegetation using a remote sensing approach. The comparison of canopy nitrogen properties and the variogram analysis of canopy nitrogen distribution provided by our study are useful for further mapping grassland canopy features and modeling grassland dynamics involving interplays among fire, large grazers, and vegetation communities.</p>10afire10agrassland canopy nitrogen10agrassland dynamics10agrazing history10aSpatial heterogeneity10aUngulate grazing1 aLing, B.1 aRaynor, E.J.1 aGoodin, D.G.1 aJoern, Anthony  uhttps://www.mdpi.com/2072-4292/11/11/1364?fbclid=IwAR3lLrrJFA3JBzN5IcRlRx-Gn7S_f-9nclPRB4H7IdDHxYQe34Ric_mraDs02826nas a2200277   4500008004100000245010400041210006900145300001200214490000600226520201300232653001502245653001502260653001202275653001102287653002102298653001202319653001102331653002002342100002302362700002002385700001702405700001802422700001302440700001702453856007802470       2013                        eng d00aEvidence of physiological decoupling from grassland ecosystem drivers by an encroaching woody shrub0 aEvidence of physiological decoupling from grassland ecosystem dr  a81630 -0 v83 a<p>Shrub encroachment of grasslands is a transformative ecological process by which native woody species increase in cover and frequency and replace the herbaceous community. Mechanisms of encroachment are typically assessed using temporal data or experimental manipulations, with few large spatial assessments of shrub physiology. In a mesic grassland in North America, we measured inter- and intra-annual variability in leaf δ13C in Cornus drummondii across a grassland landscape with varying fire frequency, presence of large grazers and topographic variability. This assessment of changes in individual shrub physiology is the largest spatial and temporal assessment recorded to date. Despite a doubling of annual rainfall (in 2008 versus 2011), leaf δ13C was statistically similar among and within years from 2008-11 (range of &minus;28 to &minus;27&permil;). A topography*grazing interaction was present, with higher leaf δ13C in locations that typically have more bare soil and higher sensible heat in the growing season (upland topographic positions and grazed grasslands). Leaf δ13C from slopes varied among grazing contrasts, with upland and slope leaf δ13C more similar in ungrazed locations, while slopes and lowlands were more similar in grazed locations. In 2011, canopy greenness (normalized difference vegetation index &ndash; NDVI) was assessed at the centroid of individual shrubs using high-resolution hyperspectral imagery. Canopy greenness was highest mid-summer, likely reflecting temporal periods when C assimilation rates were highest. Similar to patterns seen in leaf δ13C, NDVI was highest in locations that typically experience lowest sensible heat (lowlands and ungrazed). The ability of Cornus drummondii to decouple leaf physiological responses from climate variability and fire frequency is a likely contributor to the increase in cover and frequency of this shrub species in mesic grassland and may be generalizable to other grasslands undergoing woody encroachment.</p>10aEcosystems10aGrasslands10aGrazing10aLeaves10aPlant physiology10aSeasons10aShrubs10aWater resources1 aNippert, Jesse, B.1 aOcheltree, T.W.1 aOrozco, G.L.1 aRatajczak, Z.1 aLing, B.1 aSkibbe, A.M.  uhttps://journals.plos.org/plosone/article?id=10.1371/journal.pone.0081630