Abstract:Post-fire runoff and erosion from wildlands has been well researched, but few studies have researched the degree of control exerted by fire on rangeland hydrology and erosion processes. Furthermore, the spatial continuity and temporal persistence of wildfire impacts on rangeland hydrology and erosion are not well understood. Small-plot rainfall and concentrated flow simulations were applied to unburned and severely burned hillslopes to determine the spatial continuity and persistence of fire-induced impacts on runoff and erosion by interrill and rill processes on steep sagebrush-dominated sites. Runoff and erosion were measured immediately following and each of 3 years post-wildfire. Spatial and temporal variability in post-fire hydrologic and erosional responses were compared with runoff and erosion measured under unburned conditions. Results from interrill simulations indicate fire-induced impacts were predominantly on coppice microsites and that fire influenced interrill sediment yield more than runoff. Interrill runoff was nearly unchanged by burning, but 3-year cumulative interrill sediment yield on burned hillslopes (50 g m 2 ) was twice that of unburned hillslopes (25 g m 2 ). The greatest impact of fire was on the dynamics of runoff once overland flow began. Reduced ground cover on burned hillslopes allowed overland flow to concentrate into rills. The 3-year cumulative runoff from concentrated flow simulations on burned hillslopes (298 l) was nearly 20 times that measured on unburned hillslopes (16 l). The 3-year cumulative sediment yield from concentrated flow on burned and unburned hillslopes was 20 400 g m 2 and 6 g m 2 respectively. Fire effects on runoff generation and sediment were greatly reduced, but remained, 3 years post-fire. The results indicate that the impacts of fire on runoff and erosion from severely burned steep sagebrush landscapes vary significantly by microsite and process, exhibiting seasonal fluctuation in degree, and that fire-induced increases in runoff and erosion may require more than 3 years to return to background levels. Published in

Abstract:Wildfire is a major ecological process and management issue on western rangelands. The impacts of wildfire on hydrologic processes such as infiltration, runoff, and erosion are not well understood. Small-plot rainfall simulation methods were applied in a rangeland wildfire setting to determine post-fire hydrologic response. Infiltration and interrill erosion processes were measured immediately post-fire and one year following the 1999 34 400 ha Denio fire in northwestern Nevada. Plot-scale spatial and temporal variability in fire impacts was compared with adjacent unburned areas. An index of water repellency was derived and used to quantify the influence of water-repellent soil conditions on infiltration. Results indicate the impact of the fire on infiltration was localized primarily on coppice microsites directly under shrubs characterized by high surface litter accumulations. Coppice microsites had very uniform fireinduced soil water repellency with 29 of 30 plots exhibiting at least a 10% reduction in initial infiltration with an average 28% reduction. Cumulative erosion was nearly four times higher on burned coppices compared with unburned coppices. The impact of the fire on infiltration and erosion was reduced, but still evident, 1 year after fire. Significant temporal variability in infiltration between years was observed on both burned and unburned areas, complicating the interpretation of fire impacts and hydrologic recovery following wildfire. Published in

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