RIPARIAN RESTORATION ALONG THE RIO GRANDE, NEW MEXICO, USA: EFFECTS ON EVAPOTRANSPIRATION.

J.R. Thibault, J.R. Cleverly, C.N. Dahm, and D.E. McDonnell. Department of Biology, University of New Mexico, Albuquerque, NM, USA 87131

Altered hydrology and the encroachment of non-native plants threaten to eliminate the cottonwood forests along the Middle Rio Grande (MRG) of New Mexico. In this rapidly growing, semi-arid region, a critical question is how restoration might impact water budgets, particularly losses to evapotranspiration (ET). MRG riparian ET rates are poorly known. Furthermore, how ET is affected by hydrologic factors and their interannual variability is not well known. We have quantified ET using flux towers over two to three growing seasons at four riparian sites dominated by cottonwood or introduced saltcedar. While monotypic saltcedar thickets are abundant along portions of the river, saltcedar and other exotics also can make up a large part of the understory in cottonwood-dominated communities. Our ET data indicate a significant, positive correlation between leaf area index (LAI) and annual rates of ET. Flooding, river flows, water table elevations, and drought indices have not demonstrated a clear effect on annual ET rates. Our results suggest strategically managed higher flows that promote occasional overbank flooding will not significantly drive up riparian water use. Control of saltcedar and other exotics, which would lower LAI, could help restore rapidly changing cottonwood forests and simultaneously decrease riparian water use.