Submitted to: Interagency Conference on Research in the Watersheds
Publication Type: Proceedings
Publication Acceptance Date: October 1, 2008
Publication Date: N/A
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 will in turn 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 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 native bunchgrass community to one dominated by E. lehmanniana. A network of microlysimeters was deployed at Kendall to measure daily soil evaporation (ED) and an empirical model was developed to predict ED based on soil moisture (') measured at 5 cm depth and average daily solar radiation (L). Results confirmed that total ET over the growing season (ETS) was a function of season-long infiltration (IS) regardless of vegetation type, where ETS/IS was close to one. 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. These results are a first step toward understanding the initiation and persistence of E. lehmanniana invasion.