HR: 0800h
AN: H51D-1177    [Abstracts]
TI: Rainfall-Vegetation Coupling in Semi-Arid Regions: Influence of the Nitrogen Cycle on Vegetation Temporal Dynamics
AU: * Scanlon, T M
EM: tms2v@virginia.edu
AF: University of Virginia, Department of Environmental Sciences Clark Hall, Charlottesville, VA 22904 United States
AB: The ability to predict how the terrestrial environment responds to climate variability rests with understanding how rainfall, nutrient availability, and vegetation are dynamically coupled. In semi-arid ecosystems, water or nutrients are typically considered to be responsible for imposing limitations on vegetation productivity, and shifts in the specific limitation can occur abruptly over large-scale climatic gradients. For instance, in the Kalahari region of southern Africa there exists a well-defined linear relationship (R$^{2}$ = 0.94) between mean wet season rainfall and tree cover over the portion of the Kalahari that receives between 300 and 700 mm of wet season rainfall per year. In areas that receive greater amounts of rainfall, nutrients become the limiting factor, as reflected by the dominance of nutrient-poor savanna phenotypes and the fact that water use is not optimized by the ecosystem vegetation. Here vertical drainage from the root zone mobilizes nitrogen, which is considered to be the primary limiting nutrient in this region, and this perpetuates the sub-optimal (in terms of water use) canopy coverage. An analytical soil moisture model is used in conjunction with nitrogen submodel to explore the effects of changing rainfall on the vegetation structure, and in particular how hysteresis in the rainfall-vegetation relationship is mediated by the nitrogen cycle. Savanna ecosystem stability is discussed in this context.
DE: 1800 HYDROLOGY
DE: 1833 Hydroclimatology
DE: 1854 Precipitation (3354)
DE: 1866 Soil moisture
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting