EFFECTIVENESS OF CONTOUR-FELLING, MULCHING, AND SEEDING AFTER WILDFIRES IN THE COLORADO FRONT RANGE

High-severity wildfires in the Colorado Front Range can increase runoff and erosion rates by several orders of magnitude relative to unburned areas. Burn area emergency rehabilitation (BAER) treatments are typically implemented, but very few studies have quantitatively evaluated the effectiveness of these treatments (Robichaud et al., 2000). The objectives of this study were to: (1) determine if contour felling, mulching, or aerial seeding reduce hillslope-scale sediment production rates relative to untreated areas; (2) measure key site variables to determine the likely cause(s) of any reduction in hillslope erosion rates. Sediment production rates are being measured with 34 sediment fences in areas burned at high severity in the Bobcat wildfire. The installation quality of contour felling was assessed in three different fires, and the effectiveness of the contour felling technique also was assessed by measuring infiltration rates and sediment storage capacity in the trenches upslope of the downed logs.

Mulching was the only treatment that resulted in significantly lower sediment production rates. Hand mulching was effective on slopes of up to 46%. The lower sediment production rates on the mulched plots were probably due to the significantly lower percentage of bare soil relative to the other treated and untreated plots. Seed density in the aerially-seeded plots was half the target value of 440 seeds m-2, and the vegetative cover after the first growing season was less than 5%. Contributing area and percent bare soil explained nearly 70% of the variability in sediment yields in the second summer after burning. Only about half of the contour logs provided effective sediment storage due to underflow or placement off-contour; the calculated sediment storage capacity ranged from 6 to 35 t ha-1. Infiltration rates were initially higher in the trenches upslope of the contour-felled logs compared to adjacent burned areas, but this difference rapidly disappeared due to the breakdown of the hydrophobic layer and deposition in the trenches. The relative effectiveness of the mulch treatment is declining as the mulch decays and percent cover increases in the other treatments and the controls. Sediment production and percent cover are continuing to be monitored, and results from the third summer after burning will be presented.