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Title: Soil Evaporation Response to Lehmann Lovegrass (Eragrostis lehmanniana) Invasion in a Semiarid Watershed

item Moran, Mary
item Scott, Russell - Russ
item Hamerlynck, Erik
item Emmerich, William
item Holifield Collins, Chandra

Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/30/2009
Publication Date: 6/1/2009
Citation: Moran, M.S., Scott, R.L., Hamerlynck, E.P., Green, K.N., Emmerich, W.E., Holifield Collins, C.D. 2009. Soil Evaporation Response to Lehmann Lovegrass (Eragrostis lehmanniana) Invasion in a Semiarid Watershed. Agricultural and Forest Meteorology. 149:2133-2142.

Interpretive Summary: The invasion of the exotic grass, Lehmann lovegrass, into native desert grasslands is of great concern to ranchers and land managers throughout the Southwestern United States. Lehmann lovegrass displaces native grasses and reduces plant and animal diversity. There is far less known about the impact of Lehmann lovegrass invasion on ecosystem hydrology, despite the fact that it is a common invasive species in the desert southwest where water is scarce. The goal of this study was to use multiyear measurements of a naturally occurring vegetation transition to quantify the change in surface water balance associated with Lehmann lovegrass invasion. Results showed that the water loss from soil evaporation over the growing season doubled with Lehmann lovegrass invasion, which in turn will determine the persistence and management of Lehmann lovegrass in desert grasslands.

Technical Abstract: Across the western United States, warm-season grasslands are being invaded by the exotic perennial grass, Eragrostis lehmanniana (Lehmann lovegrass). The objective of this study was to quantify the change in surface water balance, particularly the evaporation from bare soil, associated with E. lehmanniana invasion. Following a protracted drought, the Kendall grassland in the USDA-ARS Walnut Gulch Experimental Watershed in southeast Arizona transitioned from a diverse, native bunchgrass community to one dominated by E. lehmanniana. A network of microlysimeters was deployed to measure daily soil evaporation (ED) in 2005 and again in 2007 (pre and post-invasion years, respectively). This was supported with continuous measurements of evapotranspiration (ET), precipitation (P), runoff (R), surface soil moisture ('), and solar radiation (L) at Kendall from 2002 to the present. An empirical model was developed to predict ED based on ' measured midday at 5 cm depth and average daily L. This was applied to years 2002-2007 during the vegetation growing season (June through October). Results confirmed that total ET over the growing season (ETS) was a function of season-long infiltration (where IS=PS-RS) for growing seasons over the past decade regardless of vegetation type, where ETS/IS was slightly greater than one in years drier than average and close to one in years with greater than average infiltration. For years of similar precipitation patterns and ETS/IS, the contribution of evaporation E to ET for the growing season (ES/ETS) doubled with the invasion of E. lehmanniana. Variation in ES/ETS ranged from 0.26 to 0.60 for years 2002-2007, where variation was related primarily to inter-annual precipitation patterns in the early season and to distinctive vegetation transformation in the middle season. These results are a first step toward understanding the ecohydrological consequences of E. lehmanniana invasion in semiarid grasslands.