Wildfire impacts on soil‐water retention in the Colorado Front Range, United States

This work examined the plot‐scale differences in soil‐water retention caused by wildfire in the area of the 2010 Fourmile Canyon Fire in the Colorado Front Range, United States. We measured soil‐water retention curves on intact cores and repacked samples, soil particle‐size distributions, and organic matter content. Estimates were also made of plant‐available water based on the soil‐water retention curves. Parameters for use in soil‐hydraulic property models were estimated; these parameters can be used in unsaturated flow modeling for comparing burned and unburned watersheds. The primary driver for measured differences in soil‐water retention in burned and unburned soils was organic matter content and not soil‐particle size distribution. The tendency for unburned south‐facing soils to have greater organic matter content than unburned north‐facing soils in this field area may explain why unburned south‐facing soils had greater soil‐water retention than unburned north‐facing soils. Our results suggest that high‐severity wildfire can “homogenize” soil‐water retention across the landscape by erasing soil‐water retention differences resulting from organic matter content, which for this site may be affected by slope aspect. This homogenization could have important implications for ecohydrology and plant succession/recovery in burned areas, which could be a factor in dictating the window of vulnerability of the landscape to flash floods and erosion that are a common consequence of wildfire.