Recovery Plan for the Northern Spotted Owl - DRAFT

disturbance, natural succession is a relatively slow process, especially duringlate seral stages. Thus, stable habitats are provided for species that cannotdisperse readily from one suitable habitat to another. Large conifers alsoprovide significant horizontal and vertical complexity. Individual trees havedeep crowns, often with trunks and limbs that are deformed or scarred bywind, lightning, or mistletoe infection. Broken tree tops and irregular branchesprovide nesting habitat for many species. The understory of shade-toleranttrees, such as western hemlock, provide further vertical divesity. Openingsdevelop in the canopy as a result of mortality of dominant trees. As the canopyopens, sunlight penetrates to the forest floor, and a diverse layer of shrubs andforbs develops, further increasing spatial complexity of the forest.Perhaps one of the most important features of old-growth forests is the greatquantity of dead wood they contain. Biomass of snags and down logs reaches80 tons per acre in stands 500 years old (Spies and Cline 1988) with aboutone-third of this in snags and two-thirds in down logs (David Perry, OregonState University, pers. comm.). Snags provide shelter and nest sites for anumber of bird and mammal species. Harris and Maser (1984) suggest thatelimination of snags in a mature, unmanaged Douglas-fir forest in the CascadeMountains would reduce the number of resident wildlife species (not includingbats) from 90 to about 80. Elimination of snags and logs would reduce thenumber to about 60. Snags are especially important to nonmigratory birds:Mannan (1977) found that about 60 percent of bird species in Douglas-firforests during the winter were cavity-nesters.Down logs are important features in terrestrial and aquatic habitats. Downlogs contribute to structural diversity, provide hiding cover for small animals,and provide moist microhabitats during dry periods. Dead and decaying woodon the forest floor contain important water reserves that buffer the effects ofthe summer drought periods typical of the region (Perry 1991). Logs are alsoimportant elements of stream ecosystems. They provide baffles and dams thatcreate pools and backwaters, increasing diversity of habitats within thesesystems. Logs and coarse woody debris also provide food for aquatic insects,which in turn provide food for predators at higher trophic levels. Fish biomassis related closely to quantity of coarse woody debris in Northwest streams(Harmon et al. 1986). Streams in managed forests typically contain few largelogs.There is not likely to be additional recruitment of extremely large diameter logsbecause rotation cycles are too short to permit the growth and mortality ofextremely large trees.Large numbers of terrestrial organisms also use coarse woody debris for foodand shelter. Important examples include the northern flying squirrel andwestern red-backed vole. These important spotted owl prey species feed onmycorrhizal fungi, which appear to be associated with decaying logs (Maser etal. 1985, Ure and Maser 1982). Other vertebrates that use logs includesalamanders, shrews, and marten (McComb 1991), as well as large numbers ofinvertebrates such as insects, slugs, and centipedes (Harmon et al. 1986,Parsons etal. 1991).Older forests are productive and valuable as wildlife habitat although theirvalue in this regard often has been underestimated. Isaac (1952) referred toold-growth as "biological deserts." Norse (1990) has suggested that thismisperception was partly a result of preoccupation with game species, whichtend to be less abundant in mature forests than in early seral environments.Because of the complex combination of characteristics required, it is doubtfulthat managed forests with short rotations and even-aged management can335