HR: 16:00h
AN: H54C-01    [Abstracts]
TI: Horizontal and vertical variability of soil moisture in savanna ecosystems
AU: * Caylor, K
EM: kcaylor@princeton.edu
AF: Princeton University, Department of Civil and Environmental Engineering, Princeton, NJ 08544 United States
AU: D'Odorico, P
EM: paolo@virginia.edu
AF: University of Virginia, Department of Environmental Sciences, Charlottesville, VA 22904
AU: Rodriguez-Iturbe, I
EM: irodrigu@princeton.edu
AF: Princeton University, Department of Civil and Environmental Engineering, Princeton, NJ 08544 United States
AB: Soil moisture is a key hydrological variable that mediates the interactions between climate, soil, and vegetation dynamics in water-limited ecosystems. Because of the importance of water limitation in savannas, a number of theoretical models of tree-grass coexistence have been developed which differ in their underlying assumptions about the ways in which trees and grasses access and use soil moisture. However, clarification of the mechanisms that allow savanna vegetation to persist as a mixture of grasses and trees remains a vexing problem in both hydrological and vegetation science. A particular challenge is the fact that the spatial pattern of vegetation is both a cause and effect of variation in water availability in semiarid ecosystems. At landscape to regional scales, climatic and geologic constraints on soil moisture availability are primary determinants of vegetation structural pattern. However, at local to landscape scales the patchy vegetation structural mosaic serves to redistribute the availability of soil moisture in ways that have important consequences for structural dynamics and community composition. In this regard, the emerging field of ecohydrology is well suited to investigate questions concerning couplings between the patchy structural mosaic of savanna vegetation and the kinds self-organizing dynamics known to exist in other light and nutrient-limited vegetation systems. Here we address the role of patchy vegetation structure through the use of a lumped model of soil moisture dynamics that accounts for the effect of tree canopy on the lateral and vertical distribution of soil moisture. The model includes mechanisms for the drying of the ground surface due to soil evaporation in the sites with no tree cover, and for the lateral water uptake due to root invading areas with no canopy cover located in the proximity of trees. The model, when applied to a series of sites along a rainfall gradient in southern Africa, is able to explain the cover fractions observed in this region.
DE: 1818 Evapotranspiration
DE: 1851 Plant ecology
DE: 1866 Soil moisture
DE: 1878 Water/energy interactions
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting