Sediment transport and soil disturbance after postfire logging.

Abstract

Recently there has been considerable debate on the practice of postfire logging, in which burned forests are entered soon after fire to recover commercially valuable trees. Proponents of the practice argue that postfire logging is part of a 'restoration package' that can be used to control erosion (e.g., contour logging) and can help to mitigate costs of rehabilitation. Opponents argue that postfire logging damages sensitive soils and can lead to excessive erosion and sediment transport. Review of the literature on postfire logging shows that very little direct scientific information can be brought to bear on this issue. A handful of hydrological studies have indicated that burned sites can be unusually sensitive to logging, especially when ground-based logging systems are used. These studies however, have demonstrated that there is considerable variation in environmental effect, due to differences in soil type, slope, weather conditions after logging, and the type of logging equipment used. In an effort to provide more information on postfire logging effects, an experiment was begun in 1997 to evaluate soil impacts and sediment transport after logging of stands burned by the 1996 Summit Fire on the Malheur National Forest. Soil disturbance and-sediment transport were measured in four replicated units in each of three postfire harvest treatments (unharvested control, partial harvest, full harvest). Displacement, compaction, and erosion were the most commonly observed types of machine-caused soil disturbance. There was a significant difference among treatments in the percentage of mechanically dishubed soil area, with controls having less area disturbed than harvested units. Despite significant soil disturbance however, little sediment transport out of experimental units occurred, due largely to: 1) the practice of hand felling; 2) logging over snow or on dry ground; 3) low slopes; 4) heavy soils; 5) no new roads; and 6) the absence of extreme weather events after logging. Visual inspections indicated that relatively little sediment left the experimental units in the short term, and that the existing road system was responsible for most sediment transport.

Citation

McIver, James D. 2003. Sediment transport and soil disturbance after postfire logging. Hydrological Science and Technology. Vol. 19(1-4): 335-348