Management Of Pacific Douglas-Fir Stands To Maintain Black-Tailed Deer Populations
Within the Pacific Northwest region of the United States, intensive, even-aged silviculture has simplified the structure and species composition of native forest stands. Within the range of the coastal Pacific Douglas-fir (Pseudotsuga menziesii), old-growth forests presently cover only 13 percent of the region; 60 percent of these remnants occur in patches less than 40 hectares in size. In this region, total land area consisting of old-growth forest before extensive logging has been estimated at 60-90 percent (Williams and Marcot 1991). As a result of intense clearcutting practices, early successional stages have become predominant and later stages have declined. Shifts in age classes of forests have been accompanied by changes in composition and abundance of fauna. Declines in population numbers, changes in conception dates, and an increase to 27 percent annual mortality (vs 5% in higher elevation old-growth stands) are a cause for implementing appropriate silvicultural practices in Douglas-fir stands managed for both timber production and a stable black-tailed deer (Odocoileus hemionus columbianus) population (McNay and Voller 1995, Brown 1992). This report will attempt to describe a fairly new and promising silvicultural method that can potentially be able to satisfy both of these criteria.
Coastal Douglas-Fir Characteristics
The habitat type that this report is concerned with is the Tsuga heterophylla zone which contains a large geographical area west of the crest of the Cascade Mountains. Much of the central portion of this zone is occupied by subclimax forests dominated by coastal Douglas-fir (Williamson 1983, Scott 1980). The rest is dominated by western hemlock (Tsuga heterophylla). The original old-growth forest, whose origin was primarily periodic, catastrophic fire, frequently had understory components of western hemlock and western redcedar (Thuja plicata). On very xeric soils, Douglas-fir may be the major species of the climax stand.
Douglas-fir is a species of medium tolerance, long life, large size, and rapid juvenile height growth. It does not sprout, but after 25 years of age bears good seed crops every 5 to 7 years. The seed disseminates well to about six tree lengths and up to one-half mile. Unmanaged stands vary between 81 and 190 cubic feet mean-annual increment at age sixty. Scott (1980) suggests that average yields of about 300 cubic feet per acre are possible in managed stands. For maximum yield, Douglas-fir is commonly grown on rotations of 40 to 60 years, depending on the site and the landowners' objectives.