@article {KNZ001524,
	title = {A test of two mechanisms proposed to optimize grassland aboveground primary productivity in response to grazing},
	journal = {Journal of Plant Ecology},
	volume = {5},
	year = {2012},
	pages = {357 -365},
	abstract = {<p>Aims Mesic grasslands have a long evolutionary history of grazing by large herbivores and as a consequence, grassland species have numerous adaptations allowing them to respond favourably to grazing. Although empirical evidence has been equivocal, theory predicts that such adaptations combined with alterations in resources can lead to grazing-induced overcompensation in aboveground net primary production (ANPP; grazed ANPP \&gt; ungrazed ANPP) under certain conditions. We tested two specific predictions from theory. First, overcompensation is more likely to occur in annually burned grasslands because limiting nutrients that would be lost with frequent fires are recycled through grazers and stimulate ANPP. Second, overcompensation of biomass lost to grazers is more likely to occur in unburned sites where grazing has the greatest effect on increasing light availability through alterations in canopy structure. Methods We tested these nutrient versus light-based predictions in grazed grasslands that had been annually burned or protected from fire for \&gt;20 years. We assessed responses in ANPP to grazing by large ungulates using both permanent and moveable grazing exclosures (252 exclosures from which biomass was harvested from 3192 quadrats) in a 2-year study. Study sites were located at the Konza Prairie Biological Station (KPBS) in North America and at Kruger National Park (KNP) in South Africa. At KPBS, sites were grazed by North American bison whereas in KNP sites were grazed either by a diverse suite of herbivores (e.g. blue wildebeest, Burchell\&rsquo;s zebra, African buffalo) or by a single large ungulate (African buffalo). Important Findings We found no evidence for overcompensation in either burned or unburned sites, regardless of grazer type. Thus, there was no support for either mechanism leading to overcompensation. Instead, complete compensation of total biomass lost to grazers was the most common response characterizing grazing\&ndash;ANPP relationships with, in some cases, undercompensation of grass ANPP being offset by increased ANPP of forbs likely due to competitive release. The capability of these very different grass-dominated systems to maintain ANPP while being grazed has important implications for energy flow, ecosystem function and the trophic dynamics of grasslands.</p>},
	keywords = {LTER-KNZ, aboveground net primary production, fire, forbs, herbivores, savanna},
	doi = {10.1093/jpe/rts020},
	url = {https://academic.oup.com/jpe/article/5/4/357/908695},
	author = {Alan K. Knapp and D.L. Hoover and John M. Blair and Buis, G. and Burkepile, D.E. and Chamberlain, A.J. and Scott. L. Collins and Fynn, R.W.S. and Kirkman, K.P. and M.D. Smith and Blake, D. and Govender , N. and O{\textquoteright}Neal, P. and Schreck, T. and Zinn, A.}
}
@article {KNZ001259,
	title = {Controls of aboveground net primary production in mesic savanna grasslands: An inter-hemispheric comparison},
	journal = {Ecosystems},
	volume = {12},
	year = {2009},
	pages = {982 -995},
	abstract = {<p>Patterns and controls of annual aboveground net primary productivity (ANPP) are fundamental metrics of ecosystem functioning. It is generally assumed, but rarely tested, that determinants of ANPP in one region within a biome will operate similarly throughout that biome, as long as physiognomy and climate are broadly consistent. We tested this assumption by quantifying ANPP responses to fire, grazing history, and nitrogen (N) addition in North American (NA) and South African (SA) savanna grasslands. We found that total ANPP responded in generally consistent ways to fire, grazing history, and N addition on both continents. Annual fire in both NA and SA consistently stimulated total ANPP (28\&ndash;100\%) relative to unburned treatments at sites with deep soils, and had no effect on ANPP in sites with shallow soils. Fire did not affect total ANPP in sites with a recent history of grazing, regardless of whether a single or a diverse suite of large herbivores was present. N addition interacted strongly and consistently with fire regime in both NA and SA. In annually burned sites that were not grazed, total ANPP was stimulated by N addition (29\&ndash;39\%), but there was no effect of N fertilization in the absence of fire. In contrast, responses in forb ANPP to fire and grazing were somewhat divergent across this biome. Annual fire in NA reduced forb ANPP, whereas grazing increased forb ANPP, but neither response was evident in SA. Thus, despite a consistent response in total ANPP, divergent responses in forb ANPP suggest that other aspects of community structure and ecosystem functioning differ in important ways between these mesic savanna grasslands.</p>},
	keywords = {LTER-KNZ, ANPP, fire, Grasslands, Grazing, nitrogen, Savannas},
	doi = {10.1007/s10021-009-9273-1},
	url = {https://link.springer.com/article/10.1007\%2Fs10021-009-9273-1},
	author = {Buis, G.M. and John M. Blair and Burkepile, D.E. and Burns, C.E. and Chamberlain, A.J. and Chapman, P. and Scott. L. Collins and Fynn, R.W.S. and Govender, N. and Kirkman, K. and M.D. Smith and Alan K. Knapp}
}
