HR: 08:05h
AN: B51A-01    [PDF]
TI: Ecohydrology and Woody Plant Encroachment: a Conceptual Framework for Evaluating Landscape Consequences
AU: * Huxman, T E
EM: huxman@email.arizona.edu
AF: Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721-0088 United States
AU: Snyder, K A
AF: USDA, Jornada Experimental Range, Las Cruces, NM 88003-8003
AU: Wilcox, B P
AF: Rangeland Ecology, Texas A&M University, College Station, TX 77843-2126
AU: Scott, R L
AF: USDA-ARS, Southwest Watershed Research Center, Tucson, AZ 85716
AU: Breshears, D D
AF: Earth and Environmental Science Division, Los Alamos National Laboratory, Los Alamos, NM 87545
AU: Small, E E
AF: Geological Sciences, University of Colorado, Boulder, CO 80309-0399
AU: Jackson, R B
AF: Department of Biology and Nicholas School of the Environment and Earth Sciences, Duke University, Durham, NC 27708-0340
AU: Pockman, W T
AF: Biology, University of New Mexico, Albuquerque, NM 87131-1091
AU: Hultine, K R
AF: Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721-0088 United States
AB: Increases in the abundance or density of woody plants in historically semiarid and arid grassland ecosystems have important implications for hydrology, ecology, and society. Using a simplified water-balance model, we propose a framework for conceptualizing how woody plant encroachment is likely to affect components of the water cycle within these ecosystems. In these systems, shrub removal has been proposed as mechanism for increasing watershed yield, but such increases are likely only in systems with shallow bedrock, riparian systems, or climatic systems where precipitation exceeds potential evapotranspiration for extended periods. In semiarid and arid systems abiotic controls on evaporation overwhelm biotic control of streamflow. In these systems, the predominant effects of woody plant encroachment that promote ecohydrological feedbacks are changes in: infiltration, depth of plant water removal, generation of transient overland flow and near-ground energy budgets that affect the ratio of evaporation (E) to transpiration (T). In these more xeric areas, the ratio of E:T is critical because it indicates the biological use of water which influences landscape structure. Increasing woody plant cover is associated with larger open interspaces, at the landscape scale the differential contribution of canopy versus interspaces may change landscape E:T. Alterations of spatial structure and ecohydrology likely influence other biogeochemical processes, such as carbon cycling. At the landscape scale, total respiration depends on the magnitude of canopy/interspace respiration flux scaled by the spatial extent of interspaces and canopy space. Canopy respiration is strongly correlated to T, while interspace respiration is largely driven by soil water availability and therefore is driven by factors that control E. Resolving the partitioning of E:T should help resolve the net effect of woody plant encroachment on other biogeochemical cycles at the landscape scale. This framework for considering the effects of woody plant encroachment highlights important ecological and hydrological interactions that serve as a basis for predicting other ecological aspects of vegetation change.
DE: 1818 Evapotranspiration
DE: 1851 Plant ecology
DE: 1860 Runoff and streamflow
SC: Biogeosciences [B]
MN: 2003 Fall Meeting