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An overstocked montane, mixedconifer forest on the west shore of the Lake Tahoe Basin was thinned using a Fecon masticator, leaving woodchips and tree shreddings on-site as mulch. No significant differences in soil compaction were found in 13 of 15 comparisons of soil-profile resistance values at several distances from the machine track and varying depths. We then watered the mastication sites with a rainfall simulator, and measured runoff, infiltration and erosion. The treatments included woodchip-covered and bare-soil plots corresponding to mulched track, as well as native grass, bare soils and relatively undisturbed soil plots. Sediment yields were greatest from the bare soils, followed by the undisturbed, grass and woodchip plots. Mastication appears to be an effective thinning treatment for overstocked forests with few discernible negative impacts on soil compaction or lake-polluting runoff.