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Impacts of fire regime on large herbivores in North American and South African grasslands

Grassland ecosystems account for up to 40% of Earth’s current terrestrial land surface, provide essential ecosystem services including carbon sequestration, are economically valuable as grazing lands, and support much of the last great megafauna on the planet. To effectively conserve and manage these ecosystems around the world, we must understand the impact of altering the key factors that regulate them. Fire and herbivory, both natural processes in grassland ecosystems, have been significantly altered by fire suppression and the loss of native large herbivores.

Of the known drivers of grassland community structure (e.g. biodiversity and species richness) and ecosystem function (e.g. productivity, nutrient cycling), fire regimes and herbivory (grazing) have been most substantially altered by human activity in grassland ecosystems throughout the world. Consequently, many grasslands are currently considered endangered, or are being invaded by woody plants. Along with collaborators from Yale University (Dr. Melinda Smith), Kansas State University (Dr. John Blair), University of New Mexico (Dr. Scott Collins), Colorado State University (Dr. Alan Knapp), Kruger National Park, and the University of KwaZulu-Natal, I am investigating the impact of altering fire and herbivory regimes on the structure and function of grassland vegetation.  Critical to this assessment is an understanding of how herbivore behavior, specifically non-random habitat selection and foraging activity across landscapes managed with different fire regimes, has the potential to shape how fire and herbivory influence the structure and function of grassland ecosystems.

Further, for ecosystems with different assemblages and diversity of native herbivores, and with different evolutionary histories of plant-herbivore interactions, the impact of altering fire and herbivory may vary. Consequently, forming a reliable global system for grassland management requires understanding how the impact of fire, herbivory, and any interactions between them may change regionally. The objective of this project is to test whether the response of grassland ecosystems to changes in fire and herbivory is comparable for two structurally similar, but evolutionarily distinct grassland ecosystems.  Ongoing long-term research (20-50+ years) in South African and North American grasslands provides a rare chance to conduct comparative research, and therefore to bring scientists and managers closer to an effective global management program. Identical sampling is being conducted at two locations in South Africa (the Ukulinga Research Farm at the University of KwaZulu-Natal, Pietermaritzburg; and the Kruger National Park) and one location in North America (Konza Prairie Biological Station in the Flint Hills of northeastern Kansas), to assess the commonalities and differences in the response of these grasslands to regime shifts in fire and herbivory.

To investigate the role of behavior in shaping the responses of grasslands to changes in fire and herbivory, my colleagues and I are assessing habitat selection and foraging activity of large herbivores (>5kg) in plots with different long-term histories of fire management (e.g. annual burning, no burning, infrequent burning).  The dominant large herbivores in these systems include bison in North American grasslands, and a suite of approximately 15 species of large herbivores in South Africa, including (but not limited to) elephants, zebra, wildebeest, giraffe, rhinoceros and impala.

Relevant publications:

Burns, C.E., S.L. Collins, and M.D. Smith. Plant community response to loss of large herbivores: Comparing consequences in a South African and a North American grassland.  Biodiversity & Conservation.  Submitted.

Knapp, A.K., C.E. Burns, R. Fynn, K. Kirkman, C. Morris, and M.D. Smith. 2006. Convergence and contingency in production-precipitation relationships in North American and South African C4 savanna grasslands. Oecologia. 149: 456-64.

Burns, C.E., A.D. Zinn, N. Govender, G. Buis, and M.D. Smith. The distribution of large herbivores in a fire-managed savanna grassland: Assessing the role of bottom-up processes. Oikos. In preparation.

Smith, M.D., C.E. Burns, S. Andelman, H. Biggs, S. Emery, N. Govender, J. Kruger, A.L.F. Potgieter, W.S.W. Trollope, and B.W. van Wilgen.  Long-term effects of fire and grazing on herbaceous vegetation of a South African savanna grassland. Journal of Ecology.  In preparation.