Extent and Severity of Postfire Soil Water Repellency within a Piñon -Juniper Ecosystem.

Recovery of juniper dominated ecosystems following fire depends on the extent that ecological processes have been altered by the junipers and the fire. Soil water repellency (WR) is a common condition in these ecosystems, and can impede site recovery by limiting infiltration and soil water storage, thereby increasing runoff and soil erosion. In this study we examine the intensity of post-fire soil WR and its influence on infiltration properties, for soils covered by juniper canopy prior to fire. Several fine scale infiltration measurements were performed along radial line transects from the bolus to twice the canopy radius, under wet and dry soil conditions. Measurements included: depth and severity of WR, soil water content, and unsaturated hydraulic conductivity, K(h), of water and a surfactant solution. We found that soil WR can persist for several months following fire, even during winter when precipitation is frequent, and exert a strong control over soil moisture dynamics.  Critical WR was related to the extent of pre-burn canopy cover. Comparison of K(h) measurements for wetting and non wetting liquids  and water drop tests indicates that subcritical WR extended from the pre-burn canopy edge to double the canopy radius. We exploit the strong relation between soil WR and pre-burn canopy cover and remote sensing imagery to upscale the spatial distribution of water repellent soils to the fire boundary scale.