HR: 17:20h
AN: B34A-05    [Abstracts]
TI: Evidence and implications of soil moisture-vegetation feedbacks in semiarid savannas
AU: Caylor, K K
EM: caylor@indiana.edu
AF: Indiana University, Department of Geography Student Building , Bloomington, IN 47405, United States
AU: * D'Odorico, P
EM: paolo@virginia.edu
AF: University of Virginia, Department of Environmental Sciences Clark Hall , Charlottesville, VA 22904, United States
AU: Okin, G S
EM: okin@geog.ucla.edu
AF: University of California, Los Angeles, Department of Geography 1255 Bunche Hall, Los Angeles, CA 90095, United States
AB: The effect of climate, soil, and vegetation on water-limited ecosystems, is exerted through the soil moisture dynamics. Unlike abiotic factors (e.g., soil texture and rainfall regime), the control exerted by vegetation composition and structure on soil moisture variability remains poorly understood. A number of field studies in dryland landscapes have found higher soil water contents in vegetated soil patches than in adjacent bare soil, providing a convincing explanation for the observed preferential establishment of grasses and seedlings beneath tree canopies. Thus, because in arid and semiarid ecosystems water is the limiting factor for vegetation, a positive feedback could exist between soil moisture and vegetation dynamics. It is still unclear how the strength of such a feedback would change under different long-term rainfall regimes. To this end, we report field observations from savanna ecosystems located along the rainfall gradient in the Kalahari, where the presence of relatively uniform sandy soils limits the effects of co-varying factors. We found that the strength of the positive vegetation-soil moisture feedback increases with increasing levels of aridity. Because positive feedbacks are often associated with the existence of alternative stable states in the dynamics of a system, we developed a minimalist modeling framework to investigate the effect of this feedback on the ecosystem dynamics. We found that, when the feedback is relatively strong, the system may exhibit two stable states corresponding to vegetated and bare soil conditions. We also show how root and soil moisture distributions affect the stability of and resilience of the vegetated (savanna) states along the Kalahari.
DE: 0439 Ecosystems, structure and dynamics (4815)
DE: 1813 Eco-hydrology
DE: 1851 Plant ecology (0476)
DE: 1866 Soil moisture
SC: Biogeosciences [B]
MN: 2007 Joint Assembly