Precommercial thinning increased diameter growth while maintaining mixedwood stands composition, 15 years after treatment

Precommercial thinning could be a valuable tool for climate-change adaptation, as it can promote stand diversity while increasing productivity. Softwood and hardwood stands are usually thinned following different methods and we lack recommendations for application in mixedwood stands. We evaluated the effects of precommercial thinning on the growth and composition of balsam fir (Abies balsamea)–birch stands dominated by paper and yellow birch (Betula papyrifera and alleghaniensis), comparing methods and production objectives (systematic release-softwood, systematic release-mixedwood, crop-tree release-mixedwood and crop-tree release-hardwood) in Québec (Canada). Precommercial thinning increased tree-level and stand-level growth, especially for both birches. Compared to the non-thinned control, thinning increased tree DBH annual increments by 60-107%, with similar results among modalities. Thinning changed initial stand composition, but mixedwood production plots composition was similar to that of the control fifteen years after treatment. Promoting diversity is often perceived to be made at the expense of wood production. Our results suggest that we can obtain both increased growth and maintain diversity. Precommercial thinning is currently suggested as an adaptation tool that can foster drought resistance. Based on our study, we suggest it could serve another purpose in climate-adapted forest management, that is, maintaining diversity and thus increasing resilience to disturbances.