What happened after the smoke cleared: onsite erosion rates after a wildfire in eastern Oregon

Robichaud, P.R.; Brown, R.E. 1999. What Happened After the Smoke Cleared: Onsite Erosion Rates after a wildfire in Eastern Oregon. In: Proceedings of the Annual Summer Specialty Conference (Track 2: Wildland Hydrology), 419-426. June 30-July 2, 1999, Bozeman, MT. Herndon, VA: American Water Resources Association.

Keywords: erosion measurement; silt fence; wildfire; nutrient loss

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Abstract: Recent fires have renewed interest in fire's effect on different components of the ecosystems, particularly erosion and soil productivity. Our objectives were to (1) determine hillslope erosion rates after a high severity wildfire in an unmanaged forest stand; (2) determine fire's short-term effects on nutrient loss. The study site was within an unmanaged forest area in the Wallowa-Whitman National Forest, Eastern Oregon. The fire consumed all downed woody debris larger than 75 mm diameter and all standing trees were killed. In addition the entire forest floor (duff) was consumed, leaving mineral soil exposed to raindrop impact and overland flow. Onsite erosion measurements were conducted for four years after the wildfire. Silt fences were used to collect eroded sediment on three slope classes (20, 30, and 60 percent), replicated twice, all within a high severity burn area. Mean first year erosion rates were 1.9 Mg ha^-1, decreasing to 0.1 Mg ha^-1 the second year, then to 0.03 Mg ha^-1 the third. No erosion occurred the fourth year. In year one, the 60 percent slope sites produced twice as much sediment as did the 20 percent slope sites. Soil nutrient losses followed the same pattern as the sediment losses. High severity wildfires can produce accelerated erosion and nutrient loss for the first year before establishment of natural regeneration.

Moscow FSL publication no. 1999d