Assessment of Forest Insect Conditions at Opax Mountain Silviculture Trial

Forest management in British Columbia requires that all resource values are considered along with a variety of appropriate management practices. For the past 100 years, partial-cutting practices were the method of choice when harvesting in Interior Douglas-fir (IDF) zone ecosystems. Along with a highly effective fire suppression program and minimal stand tending, these practices have created new and distinct stand structures. These range from low-density stands of uniform height to variable-density, multi-layered stands with patchy distributions of tree clumps and canopy gaps. However, some management practices in IDF ecosystems have created ideal conditions for epidemics of insects and diseases, which are detrimental to both stand and landscape values. The Douglas-fir beetle (Dendroctonus pseudotsugue) is the principal bark beetle attacking mature Douglas-firs (Furniss and Carolin 1980). Timber losses attributed to the Douglas-fir mortality caused by this beetle were estimated at 2.4 million m3 from 1956 to 1994. These losses occurred primarily in the province’s Southern Interior (Humphreys 1995). Visual quality values associated with stands and landscapes can be strongly affected by the removal of the principal cover species, whether by clearcut activities or widespread tree mortality. By eliminating the mature component of Douglas-fir trees within a stand, bark beetles can ultimately affect mule deer by removing their winter cover and browse. The risk of attack by the Douglas-fir beetle is determined by such stand attributes as age, species composition, size, and growth rate (B.C. Ministry of Forests and B.C. Environment 19g5a). Epidemics of Douglas-fir beetles are generally associated with factors such as root disease, tree defoliation, and excessive amounts of logging slash and debris (Furniss and Carolin 1980; Humphreys 1995). The prevalence of all three factors is strongly influenced by forestry practices, which significantly influence all forest resources. Past practices of selective logging have increased the incidence and prevalence of root diseases such as Armillaria ostoyae, Phellinus weirii, and Phaeolus schweinitzii (B.C. Ministry of Forests and B.C. Environment 19g5b). Epidemics of Douglas-fir beetles have historically followed epidemics of the western spruce budworm (Choristoneura occidentalis), known widely as the most destructive forest defoliator in western North America (Furniss and Carolin 1980). Seven epidemics of western spruce budworm have been recorded in British Columbia since 1909 (Harris et al. 1985; Koot and Hodge 1992b). The last epidemic involved 800 ooo ha at its peak in 1987, mostly in the Southern Interior of British Columbia (Koot and Hodge 1996).