Spatially-varied erosion potential from harvested hillslopes after prescribed fire in the Interior Northwest

Robichaud, P.R. 1996. Spatially-varied erosion potential from harvested hillslopes after prescribed fire in the Interior Northwest. Ph.D. dissertation. Moscow, ID: University of Idaho.

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Abstract: Considerable attention has been focused on the impacts of forest management decisions on the environment in recent decades. Burning after timber harvest is a common site preparation technique and its effect on soil erosion is of increasing concern, particularly on steep terrain. The effects of burning are not uniformly distributed on a hillslope. Methods are needed to assess the soil erosion potential on spatially-varied hillslopes so that the risk of adverse effects of management activities on water quality and aquatic habitat can be evaluated. This study presents a method to address the spatially-varied surface conditions usually found after a prescribed fire, and their influence on erosion. A laboratory study determined the factors that influence hydrophobicity, and a method to model the hydrophobicity effect was developed. Field studies were conducted to determine the spatially-varied effects of fire, and rainfall simulation was used to determine infiltration and erodibility parameters for various surface conditions. Hydrophobic soil conditions after fire occurred more often in dry coarse textured soils than in fine textured soils. A hydrophobicity index that reduced the hydraulic conductivity based on the soil texture and soil heating was developed. A forest ground cover factor based on duff thickness was developed. The amount of duff material remaining after a fire was the most important factor affecting erosion. As the amount of duff material remaining increases, erosion decreases. The amount of duff remaining and management activities were used to determine four different surface conditions after the fire. Probability distribution functions of the important factors that influence erosion were developed. A method to model spatially-varied hillslope conditions based on the sequential simulation techniques is presented.

Moscow FSL publication no. 1996i