Large woody debris volumes and accumulation rates in cleaned streams in redwood forest in southern Humboldt County, California

Abstract

Large woody debris (LWD) was inventoried in 1999 in five streams where LWD was removed in the early 1980s, and no LWD has been artificially introduced since. All study sites are second order channels near the confluence of the South Fork and main-stem Eel River, California. Watershed contributing areas range from 4.7 to 17.4 km², and mean active channel widths within study reaches range from 5.6 to 8.4 m. Vegetation is dominated by redwood (Sequoia sempervirens (D. Don) Endl.); three streams have old- and second-growth study reaches and two streams are entirely second growth. LWD volumes in old-growth reaches averaged 589 m³/ha compared to 251 m³/ha for second-growth reaches. The mean volumes in cleaned old-growth streams were significantly less (90 percent confidence level) than in undisturbed old-growth redwood streams in Prairie Creek, California (Keller and others 1985), with our reaches averaging less than a third of the mean volume in undisturbed reaches. LWD accumulation rates since cleaning were estimated using field evidence to exclude any pieces left during cleaning. Input rates averaged 13.7 m³/ha/yr for old growth and 4.2 m³/ha/yr for second growth. The discrepancy between old- and second-growth accumulation rates is primarily in the rate of input from the hillslope to the potential zone (defined as >0.5 m above the water surface and extending 1 m laterally from the active channel). Of new LWD in the active channel, 41 percent (by volume) was associated with pools and 65 percent (by volume) was trapped in debris jams.

Citation

Wooster, John; Hilton, Sue. 2004. Large woody debris volumes and accumulation rates in cleaned streams in redwood forest in southern Humboldt County, California. Research Note PSW-RN-426. Albany, CA: U.S. Dept. of Agriculture, Forest Service, Pacific Southwest Research Station. 16 p