Recovery Plan for the Northern Spotted Owl - DRAFT

The following section contains an example of the application of salvage guidelinesin the Douglas-fir/Western Hemlock Zone of the western Oregon andWashington Cascades. The example shows how specific guidelines would bedeveloped for an area where an old-growth forest stand suffered catastrophicdisturbance.Applying Salvage Guidelines in Western Washington and OregonThis example is developed for salvage of a hypothetical stand that suffered astand-replacing fire. Prior to the fire, the stand would have been classified asold-growth. Live tree densities for the original stand are in Table 3.1Snag RetentionSnag decomposition rates are related inversely to diameter. Equationsdeveloped by McComb and Ohmann (pers. comm.) predict that in westernWashington and Oregon the probability of snags less than 20-inch dbhpersisting for 100 years is near zero. Above this diameter, probabilities ofsnag survival increase rapidly for western hemlock and Douglas-fir.Snags more than 20-inch dbh are especially important for cavity-nestingbirds. Nelson (1989) found significant selection by cavity-nesters for snagsof this size. Smaller snags were not selected. Carey et al. (1991) andLundquist and Mariani (1991) also found greater use of larger snags. Sinceflying squirrels, an owl prey species, are secondary cavity users, managementfor higher densities of primary cavity-nesters will benefit squirrels and,indirectly, owls. Retention of all snags more than 20-inch dbh will maximizethe number of residual snags available to flying squirrels, while providingimportant habitat for bird species responsible for the excavation of cavitiesused by squirrels.Application of the guidelines for salvage to an old-growth forest in theOregon Cascades will provide retention of an average of 17 Douglas-fir and 9hemlock snags per acre based on mean live-tree densities (Table 3.1) forthose forests (Spies pers. comm.). Because of the diversity of initial diameters,predicting snag population survivorship is complex. However, projectionsbased on decay rate constants of Harmon et al. (1986) suggest thatabout two Douglas-fir snags per acre will remain in 100 years. The equationsof McComb and Ohmann (pers. comm.) predict that as many as four tosix Douglas-fir and one hemlock snags per acre may persist. These estimatesare within the range of densities commonly found in naturally regeneratedstands at that age (Carey et al. 1991, Huff et al. 1991, Spies andFranklin 1991).Table 3.1. Live tree densities in example old-growth western hemlock/Douglas-firstand prior to stand-replacing fire.Stem Density per Acre by Size Class2 to 4 inches 4 to 20 inches 20 to 40 inches 40 to 60 inches 60 inches+Douglas-fir 10 17 8 7 2Westernhemlock 23 33 8 1 0115