The effects of site preparation and harvesting practices on planted seedling productivity and microenvironment in southern interior dry, grassy IDF forests

Dry, pinegrass-dominated sites in the Interior Douglas-fir (IDF) zone of southern interior British Columbia are challenging to regenerate, despite ongoing improvements in nursery and silviculture practices. Using results from three separate studies (Fehr Mountain, Murray Creek, and Opax Mountain), we discuss conifer seedling survival and growth responses to silvicultural system and site preparation treatments that were applied to relieve harsh site conditions. At the flat, frost-prone site at Fehr Mountain, Douglas-fir survival was low, even where site preparation treatments resulted in exposed mineral soil. Lodgepole pine had much higher survival on the same site, and is therefore recommended for planting where there is a high risk of growingseason frost. On the steep slopes at Murray Creek, frost was of minor importance to survival and growth of lodgepole pine. Stem diameter of lodgepole pine increased as a result of chemical and mechanical site preparation treatments at both Fehr Mountain and Murray Creek, although differences at Fehr Mountain were no longer statistically significant after 11 years. Douglasfir growth also improved as a result of site preparation at Fehr Mountain, but the species could not be assessed past year 3 because of high mortality following frost damage. At Opax Mountain, Douglas-fir and lodgepole pine survived well across a range of light regimes and canopy opening sizes, as long as site preparation and planting took place promptly following harvest. To help interpret conifer seedling survival and growth responses, the effects of silvicultural system and site preparation treatments on seedling microenvironment are also discussed. For example, chemical and mechanical treatments increased soil water availability equally well by reducing the presence of pinegrass, and nighttime air temperature at seedling height also increased as a result of both types of treatment. Removal of forest floor materials in mechanical treatments resulted in short-term reductions in soil and foliar nutrient concentrations at both Fehr Mountain and Murray Creek, but there was no evidence of long-term deficiencies. At Murray Creek, however, ectomycorrhizal diversity was significantly lower in the mechanical treatment than the untreated control 28 months after planting.