HR: 1330h
AN: B52A-1026    [PDF]
TI: Climate controls on tree-grass composition and function in savannas
AU: * Williams, C A
EM: christopher.a.williams@duke.edu
AF: Duke University, 217 Hudson Hall, Duke University, Durham, NC 27709 United States
AU: Albertson, J D
EM: john.albertson@duke.edu
AF: Duke University, 217 Hudson Hall, Duke University, Durham, NC 27709 United States
AB: Climate fluctuations are believed to trigger nonlinear vegetation dynamics in savanna, such as transition from a state of grass and wood coexistence to a persistent woody state, potentially altering land surface response to climate forcing. We examine sensitivity of wood-grass composition to climate perturbations as well as changes in evapotranspiration and productivity as a function of vegetation composition by analyzing results from numerical simulations. Experimental results from our previous work motivate a simple modeling approach to dynamics of grass and woody plant functional types. The model estimates daily carbon exchanges from soil moisture limitation of potential evapotranspiration coupled to water use efficiency, and tracks daily carbon fluxes to update vegetation fractional cover of wood and grass biomass over multiple decades. We use coherence, phase, and transfer function measures to quantify the degree of coupling between rainfall with transpiration for a range of grass and woody states. A shift in vegetation composition from grass to woody dominance decreased the coherence of transpiration with rainfall at daily to weekly timescales and increased the peak phase-lag of land surface response from 2 to 7 days. We also estimate climate controls on the rate of recovery of the wood-grass state from fire and grazing disturbances.
DE: 1655 Water cycles (1836)
DE: 1818 Evapotranspiration
DE: 1851 Plant ecology
DE: 3322 Land/atmosphere interactions
SC: Biogeosciences [B]
MN: 2003 Fall Meeting