5th Symposium on Fire and Forest Meteorology and the 2nd International Wildland Fire Ecology and Fire Management Congress

Monday, 17 November 2003
Seasonal changes in soil water repellency following wildfire in chaparral steeplands, southern California
Ken R. Hubbert, USDA Forest Service, Riverside, CA; and V. Oriol
Poster PDF (191.2 kB)
Soil water repellency is particularly common in steep chaparral communities, due in part to the shallow, coarse-textured soils, and the high resin content of the organic litter. The degree and duration of soil water repellency under natural conditions may be strongly influenced by seasonal weather conditions. Consequently, the intensity of the hydrologic response is, in part, dependent on time and the soil moisture content. In September and October 2002, the Williams Fire burned 15426 ha including >90% of the San Dimas Experimental Forest. The wildfire provided an opportunity to describe changes in soil water repellency over a one-year period (Nov 2002 to Oct 2003). We sampled soil water repellency at two-week intervals using the WDPT method at the surface, 2 cm, and 4 cm depths along four transects that crossed the watershed in an east-west direction. Immediately following the wildfire, surface soils exhibited 48% moderate to high water repellency. However, moderate to high surface soil repellency always dropped below 5% following any individual winter rain event. During drying periods, moderate to high water repellency returned to less than half the pre-rain amount in the surface soil. Whereas, water repellency during drying periods was more pronounced at the 2 and 4 cm depths, returning to levels greater than one-half pre-rain amounts. Little is known about the mechanisms and speed by which hydrophilic conditions develop in periods of wet weather, nor hydrophobic conditions in periods of dry weather. Our research will provide land resource managers with a better understanding of soil water repellency on a seasonal basis; that, in turn, will provide safer conditions to those living at the urban/wildland interface.

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