Microclimate studies in silvicultural systems on the Chilcotin Plateau of British Columbia

"Group selection and irregular group shelterwood silvicultural systems are being tested as options to conserve woodland caribou (Rangifer tarandus caribou) habitat. If successful, the systems will be applied within the very dry, cold Sub-Boreal Pine-Spruce (SBPSxc) and very dry, very cold Montane Spruce (MSxv) biogeoclimatic subzones, located on the high-elevation Chilcotin Plateau of west-central British Columbia. In these harsh growing environments, partial cutting strongly influences the microclimate in terms of air and soil temperature, frost events, and snow-free dates. To examine the magnitude of this influence, three pairs of climate stations were set up in partial cuts and clearcuts, across a range of elevations, to compare microclimate conditions. Over the 7-year sample period, all blocks had frequent and sometimes severe (air temperature <-4°C) frosts throughout the growing season. As many as 58 frosts (<0°C) out of 76 nights during the period 1 June-15 August were recorded at one block. Minimum air temperatures of -12.4°C in June and -10.5°C in July were recorded. Partial cuts substantially reduced the number and severity of frosts over clearcuts; however, soil temperature and soil temperature index (ST1) were lower in partial cuts than the nearby clearcuts. Mean growing-season (15 cm) soil temperatures were less than 10°C at all locations, with clearcuts being 1.5-1.9°C warmer than nearby partial cuts. Snow-free dates were approximately 1 month later at the highest-elevation site (1620 m) in comparison to the lowest site (1290 m). This lowered soil temperatures and shortened growing seasons at the highest site. Heavier snowpacks virtually eliminated soil freezing at the highest site. The study also compared north edge, centre, and south edge microsites within one 30-m opening on each of three partial cuts. The north edge (south aspect) was the most favourable microsite for seedling growth in the partial cuts, with the highest soil temperatures, earlier snow-free dates, and more solar irradiance. Low soil temperatures and light levels made the south edge (north aspect) the least favourable microsite. Group selection and irregular shelterwoods may be applied to 181 000 ha of northern caribou habitat. Results of this microclimate study show that partial cutting clearly modifies the growing environment for lichen, tree regeneration, mushrooms, and others species. The proposed systems show promise in their ability to maintain caribou habitat and allow for some timber harvesting."