Species-specific differences in spring plant water use of invasive brush on the Edwards Plateau, Texas
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The woody encroachment of ashe juniper and honey mesquite on the Edwards Plateau is of great socio-economic and ecological importance in this semi-arid environment, since it is presumed to reduce water availability and aquifer recharge. However there is debate as to whether removal of these invaders is effective at improving water resources. More information is needed about the partitioning of species-specific water use and root water uptake distributions in this spatially complex karst environment. This study aimed to find what site factors are driving differences in brush transpiration on the Edwards Plateau during the spring season. The species-specific transpiration and pre-dawn leaf water potentials of ashe juniper, honey mesquite and the co-dominant live oak trees were monitored over a 10 week period during spring 2009. Three sites were chosen, a close canopy forest site and two open savannas with relatively deeper soils. Repeated measures mixed model statistical analysis found that species differences were larger than site differences, however one species, ashe juniper was more sensitive to site differences. More specifically juniper transpired significantly more at a very shallow rocky ashe-juniper forest site than both live oaks at the same location, and juniper, mesquite and live oak trees at deep soiled savanna sites. A non-spatial soil-vegetation-atmosphere water transfer model predicted that maximum rooting depth for all of the woody vegetation species were mostly constrained by site soil depths and we conclude that it is not likely that any of them are accessing perennially stable water supplies or significantly effecting aquifer recharge in this area.