Herbivores and Fire as Drivers of Savannas

The lab is currently a member of a large, collaborative group of ecologists, called the Savanna Convergence Experiment, representing Colorado State University, University of New Mexico, UC Santa Barbara, Kansas State University, University of KwaZulu-Natal (South Africa), Nelson Mandela Metropolitan University (South Africa), the South African Environmental Observation Network (SAEON), and the University of Botswana. Our group is investigating convergence and divergence in community patterns and ecosystem processes across the grazing ecosystems in North American and African savannas. Specifically, we are addressing questions centered on grazer-fire interactions and their impacts on plant communities and nutrient cycling across continents. Get more information about the long-term Konza-Kruger Experiment.

Our research in this collaboration uses a series of exclosures to exclude progressively smaller herbivores out of a suite of species ranging from the 3000 kg elephant to the 11 kg steenbok from areas of the savanna that differ in fire return time. Predation risk appears to be a major factor affecting the distribution of most herbivores across fire regimes (Burkepile et al, 2013, Ecosphere). For example, wildebeest, a favored prey of lions, typically select annual burns with low tree density while impala, smaller and more nimble, often select heavily vegetated unburned areas where they can outmaneuver lions an other predators when encountered. These risk-driven differences in habitat selection based result in dramatically different effects of different size guilds of herbivores on plant communities. Our partial exclosure experiments show that wildebeest and zebra control plant abundance and diversity on frequently burned areas, where they congregate for safety (Burkepile et al, in review). Yet, the smaller impala control plant diversity patterns on unburned areas, which are riskier for the larger, slower wildebeest, as the impalas’ ability to escape lions allows them to freely forage there. This set of studies is the first to document context-dependent risk effects on herbivores and plant communities from African savannas.