Effects of fuel reduction thinning and patch clearcutting on carbon stocks and plant diversity in south coastal rainforests of British Columbia

Communities are responding to increased wildfire in Canada by thinning and clearing forests in the wildland–urban interface to reduce hazardous fuel loads. The effects of these treatments on ecosystem structure and function, however, are poorly understood. This study examined effects of thinning second-growth forests, and patch clearcutting old-growth forests, on carbon stocks, stand structure, and understory diversity in the Cheakamus Community Forest, British Columbia. In the short term, thinning did not affect above- or belowground carbon stocks but increased cover and richness of understory shrubs and herbs. Conversely, thinning reduced tree diversity, creating nearly pure Douglas-fir stands. Clearcutting old growth reduced aboveground carbon stocks and most measures of plant biodiversity but had no effect on mineral soil or forest floor carbon pools. These results suggest that thinning to reduce fuel can promote understory plant diversity without harming the forest floor, but care is needed to avoid overstory simplification.