Wednesday, 9 November 2005
7

The Effects of Aerial Hydromulch on Hillslope Erosion and Plant Recovery Following Wildfire in Chaparral Shrublands.

Ken R. Hubbert, Hubbert & Associates, 21610 Ramona Ave, Apple Valley, CA 92307

The 2003 Cedar Fire consumed 284,790 acres, destroyed approximately 2,700 residences, and claimed 16 lives. Aerial hydromulch (wood and paper matrix with a non water-soluble binder) was applied by helicopter at both 50 and 100% cover to help reduce flood peaks and sediment yield downstream in the community of Peutz Valley. The 50% cover was placed on the contour at 30 m intervals. Effectiveness monitoring of aerial hydromulching was conducted to determine if the treatment was effective in preventing erosion, and to investigate if plant recovery was hindered by the treatment. To monitor hillslope erosion, we installed a total of 54 silt fences at the site. Plant recovery was measured using 1 m square grids that were separated into one hundred 10 cm2 grids. We sampled 5 plots at each of the 54 silt fences for a total of 270 individual sampling sites. Five rain gauges were placed within the perimeter of the site. Aerial hydromulch reduced erosion in both the 50 and 100% cover treatments, although the mean value for actual coverage was 51% for the 100% treatment and 30% for the 50% strip treatment. On granitic parent material, total erosion through the wet season for the 50% strip mulch treatment was 1.9 tons/acre, 1.0 tons/acre for the 100% treatment, and 4.7 tons/acre for the non-treated control. For individual rain events, we observed a positive correlation between the intensity of the individual rain event and the amount of sediment collected. It appeared that vegetation recovery was not hindered by the hydromulch. Percent cover on the 100% treatment increased from 6% in January 2004 to 27% by June 2004, whereas percent cover had increased to 26% on the untreated control. At this time, it is unknown whether any individual species were affected, or changes in plant succession occurred.

Handout (.pdf format, 9561.0 kb)

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