Long-term (1925–2015) forest structure reorganization in an actively managed temperate-boreal forest region of eastern North America

Over the last century, forest management has modified the natural disturbance regime of temperate and boreal forest regions. Consequently, this new disturbance regime may have profoundly affected the structure, composition and associated carbon stocks of forest ecosystems. The aim of this study is to document structural and compositional changes (1925–2015) in an actively managed forest region of eastern North America and their effects on above-ground biomass (AGB). We reconstructed stand structure, species composition and AGB of the preindustrial forest using 54,343 plots sampled by the Price Brothers & Company from 1924 to 1930. The present-day forest was described using 9561 plots surveyed during the most recent decadal forest inventories (1980s, 1990s, 2000s, 2010s) conducted by the Government of Quebec, eastern Canada. Between 1925 and 2015, the age structure shifted from a dominance of old-growth and mature stands (>80 years) to one of immature stands (<40 years) where early successional deciduous species increased in importance. The most striking difference was the sharp increase in stand density (>72%). Accordingly, tree diameter distribution changed markedly as a result of a strong increase of the smallest tree class to the expense of larger tree classes. Despite this structural reorganization, AGB has remained stable. Forest management history has induced a major forest structure reorganization. Aerial carbon stocks remain stable and resilient despite the strong density increase of small trees. The sharp increase in stand density could have significant impacts on biodiversity and resilience. In accordance with ecological forestry principles, the restoration of more natural forest conditions is expected to reduce the possible detrimental effects of forest management.