Serengeti Ecosystem Processes: Water or Nitrogen Control?

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A research plan of modeling and experimental field studies has been designed to determine the degree to which tropical savanna grassland ecosystems containing abundant populations of large, grazing mammals are controlled by water, nitrogen, grazing, fire, and their interactions. Modeling will focus on alternative nutrient cycling pathways as affected by those factors, coupling of cycles of different nutrients, generalizing for a broad range of site conditions and temporal scales, and simulating experiments impossible in the field. A uniform split- plot 23 factorial design will be implemented at four experimental field sites over substantial ranges of precipitation, soil fertility, soil salinity, primary production, fire, and herbivory representative of a broad span of arid to subhumid ecosystems. The basic design will be augmented by extensive plots whose purpose will be to provide better coverage for inherent variability of physical factors such as climate. Twelve hypotheses about the balances of controlling factors will be tested with model simulation and field data on aboveground and belowground net primary productivity, herbivory, plant water and N status, litterfall, decomposition, and mineralization. Grazers as controllers of nitrogen cycling and hydrologic balances will be evaluated as an integral component of modeling and experiments. This project continues to enjoy excellent support at the home institution. Additionally, the host country science establishment remains committed to its past levels of receptivity, assistance and participation. The project group is excellent and well versed in the subject ecosystem and the necessary, but difficult, remote logistics. It is reasonable to expect that findings of major significance in fundamental ecology will continue to be produced by this work. Similarly, one can expect that the resultant information will be useful in range management, both in Kenya and elsewhere. The Ecosystem Studies Program recommends that the first year of this five-year continuing award be supported.