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ARS Home » Pacific West Area » Tucson, Arizona » SWRC » Research » Publications at this Location » Publication #189614


item Scott, Russell - Russ
item HUXMAN, T.
item Goodrich, David - Dave

Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: 10/1/2005
Publication Date: 12/5/2005
Citation: Scott, R.L., Huxman, T.E., Williams, D.G., Goodrich, D.C. 2005. Ecohydrological impacts of woody phreatophyte invasion within a semiarid riparian environment. {abstract}. Eos. Trans. AGU, 86(52), Fall Meet. Suppl. Abstract B23A-1046.

Interpretive Summary:

Technical Abstract: 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