TY - JOUR T1 - Addition of multiple limiting resources reduces grassland diversity JF - Nature Y1 - 2016 A1 - Harpole, W. S. A1 - L.L. Sullivan A1 - Lind, E.M. A1 - Firn, J. A1 - P. Adler A1 - E.T. Borer A1 - Chase, J. A1 - Fay, P.A. A1 - Hautier, Y. A1 - Hillebrand, H. A1 - MacDougall, A.S. A1 - Seabloom, E.W. A1 - Williams, R. A1 - J.D. Bakker A1 - Cadotte, M.W. A1 - Chaneton, E.J. A1 - Chu, C. A1 - Cleland, E.E. A1 - Antonio, C. A1 - Davies, K.F. A1 - Gruner, D.S. A1 - Hagenah, N. A1 - Kirkman, K. A1 - Knops, J.M.H. A1 - Kimberly J. La Pierre A1 - McCulley, R.L. A1 - Joslin L. Moore A1 - J.W. Morgan A1 - Prober, S.M. A1 - A. Risch A1 - Schuetz, M. A1 - Stevens, C.J. A1 - Wragg, P.D. AB -
Niche dimensionality provides a general theoretical explanation for biodiversity—more niches, defined by more limiting factors, allow for more ways that species can coexist1. Because plant species compete for the same set of limiting resources, theory predicts that addition of a limiting resource eliminates potential trade-offs, reducing the number of species that can coexist2. Multiple nutrient limitation of plant production is common and therefore fertilization may reduce diversity by reducing the number or dimensionality of belowground limiting factors. At the same time, nutrient addition, by increasing biomass, should ultimately shift competition from belowground nutrients towards a one-dimensional competitive trade-off for light3. Here we show that plant species diversity decreased when a greater number of limiting nutrients were added across 45 grassland sites from a multi-continent experimental network4. The number of added nutrients predicted diversity loss, even after controlling for effects of plant biomass, and even where biomass production was not nutrient-limited. We found that elevated resource supply reduced niche dimensionality and diversity and increased both productivity5 and compositional turnover. Our results point to the importance of understanding dimensionality in ecological systems that are undergoing diversity loss in response to multiple global change factors.
VL - 537 UR - https://www.nature.com/articles/nature19324 JO - Nature ER - TY - JOUR T1 - Responses to fire differ between South African and North American grassland communities JF - Journal of Vegetation Science Y1 - 2014 A1 - Kirkman, K. A1 - Scott. L. Collins A1 - M.D. Smith A1 - Alan K. Knapp A1 - Burkepile, D.E. A1 - Burns, C.E. A1 - Fynn, R.W.S. A1 - Hagenah, N. A1 - Koerner, S.E. A1 - Matchett, K.J. A1 - Thompson, D.I. A1 - K.R. Wilcox A1 - Wragg, P.D. KW - Community ecology KW - Divergence KW - Fire frequency KW - Konza Prairie Biological Station KW - Mesic grassland KW - nitrogen KW - Nutrient addition KW - Richness KW - tallgrass prairie KW - Ukulinga Research Farm AB -Question Does fire frequency affect mesic grassland plant community structure and composition similarly in North America and South Africa? Location Konza Prairie Biological Station (KNZ), Kansas, USA, and Ukulinga Research Farm (URF), KwaZulu-Natal, South Africa. Methods Plant community structure and composition were compared among annually burned, unburned and intermediate treatments within two long-term fire frequency manipulation experiments in native grasslands in North America and South Africa using comparable methodology over a 5-yr period. Because fire may reduce soil nitrogen (N) availability and thus affect plant community structure, N additions were superimposed on the fire treatments as a means of assessing direct vs indirect mechanisms driving responses to fire. Results The total number of species was higher at URF (183) than at KNZ (57). Overall divergence in plant community response to fire frequency occurred despite similar responses to nutrient additions. At KNZ, more frequent fire resulted in dominance by a few, tall, deep-rooted rhizomatous grasses (e.g. Andropogon gerardii). On unburned sites, shorter, more shade-tolerant species such as Poa pratensis increased in abundance, although A. gerardii remained dominant. Species richness increased with decreasing fire frequency at KNZ. At URF, frequent fire resulted in short, diverse grassland weakly dominated by a range of grass species, including Themeda triandra, Tristachya leucothrix and Hyparrhenia hirta. Decreasing fire frequency reduced species richness and resulted in dominance by a few, relatively tall caespitose grasses such as Aristida junciformis. There was a complete turnover of dominant species between annually burned and unburned treatments at URF, while at KNZ A. gerardii and Sorghastrum nutans occurred across the range of treatments. N addition reduced species richness in both sites. Conclusions Different responses to fire frequency between KNZ and URF are likely linked to the dominant species and their characteristic traits, including height and method of clonal reproduction, with the rhizomatous growth form of A. gerardii dominating the North American grassland. South Africa does not have an equivalent grass species; instead, a range of tufted, non-rhizomatous species dominate across the fire frequency treatments at URF. Reductions in soil N due to frequent fire did not appear to be a common mechanism driving responses in community composition in these two grasslands.
VL - 25 UR - https://onlinelibrary.wiley.com/doi/abs/10.1111/jvs.12130 ER - TY - JOUR T1 - Controls of aboveground net primary production in mesic savanna grasslands: An inter-hemispheric comparison JF - Ecosystems Y1 - 2009 A1 - Buis, G.M. A1 - John M. Blair A1 - Burkepile, D.E. A1 - Burns, C.E. A1 - Chamberlain, A.J. A1 - Chapman, P. A1 - Scott. L. Collins A1 - Fynn, R.W.S. A1 - Govender, N. A1 - Kirkman, K. A1 - M.D. Smith A1 - Alan K. Knapp KW - ANPP KW - fire KW - Grasslands KW - Grazing KW - nitrogen KW - Savannas AB -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 (28–100%) 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 (29–39%), 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.
VL - 12 UR - https://link.springer.com/article/10.1007%2Fs10021-009-9273-1 ER -