The use of large plot rainfall simulation to investigate

In this study, large scale rainfall simulation was used to evaluate runoff generation from canopy and intercanopy areas within an ashe juniper woodland of the Edwards Plateau. One 3 x 12 m site was established beneath the canopy of mature ashe juniper trees and two sites were established in intercanopy areas. At the base of each plot a trench was constructed for capturing and monitoring shallow subsurface flow. Rainfall simulations on the juniper site produced little surface runoff even though rainfall intensity exceeded 145mm/hour on some occasions. A total of 82.6% of the water applied to the juniper dominated site was accounted for as shallow subsurface flow. The dynamic nature of shallow subsurface flow indicate this process is driven chiefly by macropore flow. On the intercanopy site, 12.67% of the water left the site as surface runoff and ≤3% left as shallow subsurface flow. Large root channels and conduits, which were not present on the intercanopy site, within the soil may promote shallow subsurface flow beneath the juniper canopy. This study is the first to document and suggest shallow subsurface flow occurs on Texas rangelands. The results of this experiment indicate shallow subsurface flow is an important mode of runoff generation on the Edwards Plateau.