Recovery Plan for the Northern Spotted Owl - DRAFT

II. Review of Natural Vegetation and StandDevelopment - History of ForestManagementA. Coastal Forests and Western Cascades ofOregon and WashingtonForests on federal lands in the western Cascades and Coast Range mountainsof Oregon generally are classified in the western hemlock and silver fir zones byFranklin and Dyrness (1973). There is generally plentiful moisture throughoutthese zones, and plant associations range from oxalis and sword fern on moistsites to Douglas-fir, ocean spray, vine maple, and salal on drier sites. Olderstands in these forests often have a well-developed understory of shrubs andhardwoods such as vine maple, yew, bigleaf maple, salal, salmonberry,rhododendron, hazel, ocean spray, and huckleberry. Conifers in the understoryare primarily western hemlock and western red cedar on moist sites.Grand fir and Douglas-fir may occur on dry sites, and silver and noble fir atupper elevations.1. Natural Forest DevelopmentNatural disturbances in these forests occur over a range of sites, frequencies,intensities, and patterns. Under natural conditions, stand replacement firesoccurred at intervals of about 95 years to more than 500 years (Appendix F)with the longer intervals on moist sites. These fires often burned many thousandsof acres. The mortality of the overstory within these extensive bumsvaried considerably (Spies and Franklin 1991, Morrison and Swanson 1990).Groups of trees and scattered individual trees often survived more than onefire. Thus, the Douglas-fir overstory in old-growth forests is often multi-aged(Franklin and Hemstrom 1981). Even with fire suppression, large fires canoccur, for example, the Tillamook bum in the 1930s and the Oxbow fire in the1960s.Wind effects are most severe on ridge tops and near the coast and ColumbiaGorge, although severe storms like the Columbus Day Storm of 1961 causedmajor disturbances on a wide range of sites (Ruth and Harris 1979). Windeffects are often small-scale, blowing down small groups (less than one acre)and individual trees and breaking tops: although entire stands (more than 20acres) may be blown down. Insect populations (bark beetles) often increaseafter fire or blowdown.Root and stem diseases are widespread, but they generally occur on a smallerscale than wind and fire. They slowly kill groups of trees. Over extensive areas,root disease may affect more than 10 percent of the entire area. Other agentsof disturbance include ice storms, which mostly break the tops of stands ofyoung trees, and mass movement such as landslides, which are importantlocally.Individual trees also die because of competition among trees (Drew andFlewelling 1979). Self-thinning is a natural part of stand development andoccurs much more quickly on more productive sites than on poor sites. Rateof self-thinning is dependent on species composition and stand density.492