Woody debris

1. Maximum rate of cut that would provide a hillslope landslide rate of <20% over background, assuming no areas are protected by no-cut buffers .. Summary Downstream impacts to aquatic environments and property generally occur as cumulative watershed impacts, which are usually caused by changes in the transport of woody debris, water, and sediment through a watershed. The downstream cumulative impacts that are likely to accrue from implementation of the Sustained Yield Plan / Habitat Conservation Plan for the properties of The Pacific Lumber Company, Scotia Pacific Holding Company, and Salmon Creek Corporation (referred to here as the " SYP/HCP ") are thus assessed by evaluating the plan's likely effects on woody debris, water, and sediment. As currently written, the SYP/HCP will contribute to increased severity of cumulative impacts arising from an inadequate woody debris regime over the 50-year-period considered by the SYP/HCP. This increased level of cumulative impact will occur primarily because (1) a high proportion of the few remaining trees large enough to provide properly functioning wood will be cut from areas of residual old-growth within one old-growth tree height of streams; (2) there will be permanent removal of effective wood from Class III streams; (3) woody debris loadings in Class II channels will be permanently held at 21% or less of the levels that would be present in unmanaged stands; and (4) woody debris loadings in Class I channels will be permanently held at 39% or less of the levels that would be present in unmanaged stands. Existing cumulative impacts that will be aggravated by the plan's effects on woody debris loadings include (1) increased magnitude and frequency of downstream flooding due to decreased storage of flood waters in upstream channels; (2) increased destabilization and aggradation of downstream habitats important to coho salmon and other Pacific salmonids due to increased incidence and mobility of debris flows and increased incidence of gullying; (3) continued impairment of downstream water quality due to increased gullying of Class III channels; and (4) increased damage to downstream properties due to increased incidence and mobility of debris flows. Mitigation of this suite of impacts will not be possible because it would require that the roles of large wood be fulfilled through other means, but no other means are available for fulfilling those roles. The discrepancy between the calculated rates of debris input and those reported by the SYP/HCP arise, in part, because the …