Hydrologic characteristics of vegetation types as affected by prescribed burning

The objective of this study was to determine how rangeland hydrology of oak, juniper, bunchgrass and shortgrass vegetation types is altered by fire. The research was conducted at the Sonora Agricultural Experiment Station on the Edwards Plateau, Texas. Infiltration rate and interrill erosion were measured using a drip-type rainfall simulator. Terminal infiltration rates of unburned areas were significantly greater on sites dominated by oak (Quercus virginiana Mill.) (200 mm hour-1) or juniper (Juniperus ashei Buchh.) (183 mm hour-1) than on sites dominated by bunch-grass (146 mm hour-1) or shortgrass (105 mm hour-1). Terminal infiltration rates on burned areas were significantly reduced on sites dominated by bunchgrass (110 mm hour-1), shortgrass (76 mm hour-1), and on oak sites that were cut and burned (129 mm hour-1). Soil organic matter content (r = .61), total organic cover (r = .59), and aggregate stability (r = .53) were the variables most strongly correlated with infiltration rate. Measured soil structure properties were not altered by fire, therefore, differences in infiltration rate between unburned and burned treatments were attributable to variations in the amount of cover. The terminal infiltration rate of cut and burned juniper sites (162 mm hour-1) was not changed significantly after the fire because the associated good soil structure properties allowed rapid infiltration even after cover was removed. Good soil structure properties were also present on the oak sites, but the infiltration rate significantly decreased as a result of the temporary hydrophobic nature of the soil on this site after burning. Prior to burning, interrill erosion was much lower under the tree sites (oak = 2 kg ha-1; juniper = 34 kg ha-1) than on bunchgrass (300 kg ha-1) or shortgrass (1,299 kg ha-1) sites. After burning, interrill erosion significantly increased for all vegetation types (shortgrass = 5,766 kg ha-1; bunchgrass = 4,463 kg ha-1; oak = 4,500 kg ha-1; juniper = 1,926 kg ha-1). Total organic cover (r = -.74) and bulk density at 0-30 mm (r = .46) were most strongly correlated with interrill erosion.