HR: 1340h
AN: B23A-1036 INVITED     [Abstracts]
TI: Ecohydrological Impacts of Woody Phreatophyte Invasion Within a Semiarid Riparian Environment
AU: * Scott, R L
EM: rscott@tucson.ars.ag.gov
AF: USDA-ARS, 2000 E. Allen Road, Tucson, AZ 85719 United States
AU: Huxman, T E
EM: huxman@email.arizona.edu
AF: Department of Ecology and Evolutionary Biology University of Arizona, University of Arizona, Tucson, AZ 85721 United States
AU: Williams, D G
EM: dgw@uwyo.edu
AF: Departments of Renewable Resources and Botany, University of Wyoming, Laramie, WY 82071 United States
AU: Goodrich, D C
EM: dgoodrich@tucson.ars.ag.gov
AF: USDA-ARS, 2000 E. Allen Road, Tucson, AZ 85719 United States
AB: Along the Upper San Pedro River in southeastern Arizona deep-rooted woody phreatophytes such as the non-native Tamarix ramosissima (salt cedar) and the native Prosopis velutina (velvet mesquite) are expanding their range, but we have little understanding about how this change in vegetation composition will change the cycling of water and nutrients in these riparian ecosystems. We compared water and carbon dioxide fluxes over a grassland, a grassland-shrubland mosaic, and a fully developed woodland to evaluate potential consequences of woody plant encroachment on important ecosystem processes. Using fluxes measured by eddy covariance in 2003 we found that ecosystem evapotranspiration (ET) and net ecosystem exchange of carbon dioxide (NEE) increased with woody plant encroachment. The dominant grass or shrub at all sites accessed groundwater to some degree, but groundwater use increased with woody plant density. Greater access to groundwater for the deeper-rooted woody plants apparently decouples ecosystem evapotranspiration from gross ecosystem production (GEP) with respect to precipitation. The woody plants were better able to use the stable groundwater source, which increased net carbon dioxide gain during the dry periods by maintaining plant function. However, this enhanced plant activity leads to substantial accumulation of leaf litter on the soil surface that, during rainy periods, may lead to high microbial respiration rates that offset these photosynthetic fluxes. These initial data suggest that the ability of the woody plants to better exploit water resources in riparian areas results in enhanced carbon sequestration at the expense of increased groundwater use under current climate conditions, but the potential does not scale specifically as a function of woody plant density.
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0428 Carbon cycling (4806)
DE: 0483 Riparian systems (0744, 1856)
DE: 1813 Eco-hydrology
DE: 1818 Evapotranspiration
SC: Biogeosciences [B]
MN: Fall Meeting 2005