Water Repellency in Soils after Cool and Warm Season Prescribed Fires in Emory Oak Savannas of Southwest New Mexico.

Oak-savannas comprise over 80,000 km² in the mountains and high valleys of the  southwestern United States and northern Mexico.  Fire, which was once the most important natural disturbance in this system, has been excluded due to over-grazing and fire suppression practices.  Questions concerning the seasonality of burn treatments and the overall effects of these treatments on physical and ecological processes are being addressed in a collaborative interdisciplinary study to determine the effects of cool-season and warm-season prescribed burning on a southwestern oak-savanna ecosystem.  Twelve small watersheds in the Peloncillo Mountains of southwestern New Mexico have been monitored for seven years to provide adequate hydrologic calibration data prior to seasonal prescribed burning treatment application.  These watersheds are grouped in four replicated blocks, each consisting of a cool-season treatment, a warm-season treatment and a control watershed.  The cool season burns were conducted in March, 2008, and the warm season burns in May, 2008. Average fire temperature ranged from 293^o C in litter to 693 ^o C in manzanita. Because of low fuel loads, low air temperatures, and moderate relative humidity the fires were low to moderate in severity. The corresponding water repellency on the coarse-textured soils was mostly non-existent. High levels of water repellency were noted under woody debris and beargrass clumps.  This paper will discuss the characteristics and behavior of the cool-season burn treatment, summarize burn intensity and severity estimates, and describe the measured water repellency.