Recovery Plan for the Northern Spotted Owl - DRAFT

After 100 years residual snags will be well decayed and about half will bemore than 15 feet tall (Spies and Franklin 1991). Not all snags will havecavities for flying squirrels. In mature forests (80 to 195 years old) inwestern Oregon and Washington, an average of 8 percent of snags morethan 20-inch dbh contained natural cavities and 24 percent had excavatedcavities (Spies and Franklin 1991). Even if natural and excavated cavitieswere in different snags, only about 30 percent of all snags would havecavities, and post-fire retention of all snags more than 20-inch dbh may onlyprovide one or two residual snags per acre with cavities. It is prudentinitially to retain maximum numbers of large snags to provide for long-termneeds of cavity-nesters, including flying squirrels.In this scenario, approximately 17 Douglas-fir and 44 hemlock stems peracre between 4- and 20-inch dbh would be available for salvage. Thevolume probably would be similar to that removed during commercialthinning. Application of the snag guideline provides for maximum densitiesof snags at 100 years, while allowing removal of smaller diameter stemswhich would not persist.Log RetentionIn the western Oregon Cascades and Oregon Coast Range, most naturallyregenerated conifer forests contain 9 to 18 tons per acre of down logs at 100years of age (Spies et al. 1988). Assuming a 3 percent annual decay rate(Spies et al. 1988) for 100 years, about 180 tons per acre of CWD need to beretained to provide this quantity. Therefore, approximately 50 to 75 percentof the original standing biomass of 270 to 360 tons per acre (Spies et al.1988) must remain on the site. Down logs with diameters greater than 20inches should be retained selectively. These larger logs will decay relativelyslowly and provide habitat for forest floor mammals during a relatively longtime period (Carey and Raphael pers. comm.).If regeneration is delayed, significantly greater amounts of CWD must beretained to compensate for delaying CWD production by the new stand 100years hence. Thus, when areas are salvaged, it is extremely important toregenerate new stands as quickly as possible.If green trees, snags, and logs are on site following the disturbance, guidelinesto retain all green trees and all snags with diameters greater than 20inches will be applied first. The guideline for logs will reflect the amount ofbiomass left in the form of snags since this standing material eventually willbecome available as CWD. For example, if snags were estimated to provide90 tons per acre, this amount will be deducted from the 180 tons per acrerequired to be left as logs.In any case, where the combined biomass of snags and logs greater than 20inches in diameter do not meet retention objectives (e.g., 180 tons per acrein western Oregon and Washington Cascades), additional logs and/or snagsof smaller diameter will be retained.Guidelines to Reduce Riskss of Large-Scale Disturbance. Large-scaledisturbances are natural events, such as fire, that can eliminate owl habitat onhundreds or thousands of acres. Certain risk management activities, if properlyplanned and implemented, may reduce the probability of these majorstand-replacing events. There is considerable risk of such events in DCAs inthe eastern Oregon and eastern Washington Cascades and the CaliforniaCascades provinces and a lesser risk in the Oregon and California Klamathprovinces (as documented in Appendix F). Elevated risk levels are attributed to116