Changes in species composition 20 years after selection cutting in northern hardwood and mixedwood stands

Temperate forests of northeastern North America provide key ecosystem services but are increasingly affected by multiple stressors, including climate change, biological invasions, pollution, and land-use impacts, potentially altering species composition and thus productivity and sustainability of these forests. This study examined 20-year compositional changes in 233 uneven-aged forest stands subjected to single-tree selection (STS) cutting or left unmanaged, encompassing hardwood and mixedwood stands across southern Quebec, Canada. Analyses were based on species-specific proportions of basal area across three developmental stages: saplings, recruit trees, and pre-existing canopy trees. Results indicated that compositional shifts primarily occurred in younger cohorts (saplings and recruits), while canopy composition remained relatively stable. In hardwood stands, the proportion of sugar maple ( Acer saccharum Marsh.) declined among recruits and saplings, whereas that of American beech ( Fagus grandifolia Ehrh.) increased, indicating a gradual replacement dynamic. Yellow birch ( Betula alleghaniensis Britt.), a mid-tolerant species, remained underrepresented in these stages, though it was promoted by STS compared with the unmanaged control. In mixedwood stands, yellow birch dominated the canopy, but balsam fir ( Abies balsamea (L.) Mill.) became prevalent among recruits and saplings. These trends were observed in both STS and control plots, suggesting that harvest operations had marginal impact on forest composition. Rather, some broader ecological drivers, beyond silvicultural practices alone, were likely more influential. Our results point toward an impending shift in species dominance, particularly in hardwood stands. Adaptive silvicultural strategies, combined with consideration of emerging biotic stressors, will be essential to sustain desired species composition and associated ecosystem services.