Grasslands and savannas occupy one eighth of the land surface on Earth, are economically important as grazing lands, and are highly impacted by human activities. They also have tremendous conservation value and support most remaining large native grazing animals in the world, particularly in Africa. A fundamental understanding of the factors most important for sustaining savanna grasslands, including their natural fire and grazing regimes, is required for their management and conservation. Scientists have questioned whether grasslands in different regions function similarly. Convergence in functioning would mean that ecological understanding and conservation strategies could be generalized for savanna grasslands worldwide. But contingent factors specific to a region, such as differences in evolutionary history or the types of grazers present, may lead to unique responses in some savanna grasslands. The goal of this research is to compare responses of key ecological processes to fire and grazing in North American and South African savanna grasslands. Scientists will take advantage of three ongoing, long-term experiments that manipulate fire return interval and the presence of large grazers. Responses of plant productivity, plant diversity and nutrient cycling will be compared, and the mechanisms underlying responses, such as differences in plant traits or evolutionary histories, will be assessed.
Comparative research elucidating the consequences of human alterations of fire and grazing regimes worldwide is needed to enable development of management strategies that can insure the sustainability of ecologically and economically important savanna grasslands. This research will provide the basic knowledge necessary to do so, as well as afford training and important global and cultural experiences for young scientists, graduate students and undergraduates. Finally, though collaborations that are already established, results will be made available to scientists and managers in South Africa.
The purpose of this project was to determine the degree of generality we can derive from site-based experimental research. In our case, we wanted to know if savanna grasslands in Kansas, USA, Kruger National Park, South Africa, and Pietermaritzburg, South Africa responded similarly to key drivers of grassland processes: fire frequency, grazing by native herbivores and interannual climate variability. Knowing this would allow us to determine how much we can generalize the results of our research from one similar ecosystem to another. Overall, we found that ecosystem level processes (net primary production and soil nitrogen availability) responded similarly to fire frequency in Kansas and Kruger. In contrast, some plant community responses differed and others were similar between these geographically disparate systems. For example, grassland biodiversity increased with grazing in both study systems. However, grassland response to fire differed in North America and South Africa. Biodiversity was highest in annually burned grasslands in South Africa and lowest in annually burned sites in Kansas. These differences reflect the much longer history of multispecies of herbivores in Kruger compared to Kansas. Overall, our results showed that many responses between these systems were surprisingly similar despite vast differences in evolutionary history. Therefore, we can detect many generalities in response to common drivers in North American and South African savanna grasslands. This international project presented many opportunities for US students to gain international experience and learn about research in South Africa.
