Short-term carbon, biodiversity, and forest structure responses to a fire risk reduction treatment in Interior British Columbia, Canada

Wildfire risk reduction treatments such as thinning and prescribed burning are becoming commonplace across British Columbia forests in response to the increase in frequency and severity of wildfires. However, investigations of their effects on ecosystem structures and functions have been lacking to date. To help address this, we examined short-term effects of a thinning and burning treatment on predicted wildfire risk as well as carbon stocks, forest structure, and plant biodiversity in West Arm Provincial Park, near Nelson, British Columbia, Canada. The treatment met the goal of reducing the wildfire risk rating. In the short-term, forest floor depth and carbon stocks were 73% (4.1 cm) and 51% (12.20 Mg ha –1 ) less, respectively, in the treatment than the control. The aboveground tree carbon pool was also reduced, with average stocks in the treatment one-third that of the control (14.66 ± 8.72 Mg ha –1 versus 43.63 ± 16.56 Mg ha –1 , respectively). Herb cover increased and moss cover decreased, and the species composition of the plant community changed, including an increase in plants associated with disturbances. The thin-burn treatment resulted in high tree mortality and damage rates, and simplified tree species diversity and vertical stand structure compared with the control. On our site, a thin-only treatment would have eliminated tree mortality due to follow-up burning, but would have been ineffective at reducing fire hazard based on the intensity of the applied burn. Our findings indicate the thin-burn treatment had trade-offs, where reduced fire risk came at ecological costs, highlighting the need for prescriptions to consider potential effects on carbon stocks and plant communities, and to be based on local conditions. We emphasize that our study was preliminary and that further monitoring is required to assess long-term results.