PS 78-80
Divergent responses to fire in South African and North American grassland communities

Friday, August 9, 2013
Exhibit Hall B, Minneapolis Convention Center
Kevin P. Kirkman, School of Life Sciences, University of Kwazulu-Natal, Scottsville, South Africa
Scott L. Collins, Department of Biology, University of New Mexico, Albuquerque, NM
Melinda D. Smith, Graduate Degree Program in Ecology, Colorado State University, Ft. Collins, CO
A.K. Knapp, Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO
Deron E. Burkepile, Biological Sciences, Florida International University, North Miami, FL
Catherine E. Burns, San Francisco Bay Bird Observatory, Milpitas, CA
Richard W.S. Fynn, Okavango Research Institute, University of Botswana, Maun, Botswana
Nicole Hagenah, School of Life Sciences, University of Kwazulu-Natal, Scottsville, South Africa
Sally E. Koerner, Department of Biology, Colorado State University, Durham, CO
Katherine Matchett, Grassland Science, School of Biological and Conservation Sciences, University of KwaZulu-Natal, Pietermaritzburg, South Africa
Dave Thompson, Ndlovu Node, SAEON, Phalaborwa, 1390, South Africa
Kevin Wilcox, Department of Biology, Colorado State University, Fort Collins, CO
Peter D. Wragg, Department of Ecology, Evolution, and Behavior, University of Minnesota, St Paul, MN

Does fire frequency affect plant community structure and composition similarly in grasslands in North America and South Africa? Plant community structure and composition were compared among annual, intermediate and unburned treatments within two long-term fire manipulative experiments in native grasslands at Konza Prairie Biological Station (KNZ), Kansas, USA and Ukulinga Research Farm (URF), KwaZulu-Natal, South Africa, using identical methodology over a five year period. Because fire may reduce soil nitrogen (N) availability and thus affect community structure, N additions were superimposed on the fire treatments as a means of assessing direct vs. indirect mechanisms driving responses to fire.


Although richness was higher at URF (157) than at KNZ (83), there was divergence in plant community response to fire frequency despite convergent responses to nutrient additions. At KNZ, frequent fire resulted in dominance by few, tall, deep-rooted rhizomatous grasses (e.g. Schizachyrium scoparium and Andropogon gerardii). On unburned sites, shorter, shade tolerant species such as Poa pratensis increased, although A. gerardii remained dominant. Richness increased with decreasing fire frequency at KNZ. At URF, frequent fire resulted in short, diverse grassland weakly dominated by a range of species, typified by Themeda triandra. Decreasing fire frequency reduced richness and resulted in dominance by relatively tall caespitose grasses such as Aristida junciformis. N addition reduced species richness in both sites. The divergent response to fire frequency is 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 at KNZ. URF 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.