Using forestry archives to assess long-term changes in forest landscape age structure and tree composition (1950–2020) in eastern Canada

Global forest landscapes are undergoing profound changes driven by the influence of multiple interacting factors, including forestry, natural disturbances, and climate change. Monitoring and understanding these complex dynamics is challenging due to the lack of data at the spatiotemporal scale at which changes occur (i.e., millions of ha over decades). In this study, we analyzed forest management plans from the 1950s alongside contemporary forest inventories to track changes in age structure and tree species composition across 18 large landscapes covering 3.8 million hectares of eastern Canada's forests. Using cluster analysis, we grouped the 18 studied landscapes into four broad ecological regions (i.e., northern and southern boreal and western and eastern temperate mixed forests) characterized by similar forest composition in the 1950s and subsequent disturbance regimes from 1950 to 2020. The boreal regions transitioned from old-growth-dominated landscapes to those dominated by young stands, mainly due to clearcutting. This transformation was associated with declines in spruces and paper birch and increases in poplars, balsam fir, and jack pine. In contrast, the temperate regions—already logged before the 1950s—experienced subtler age structure changes. Birches and black spruce declined in those forests, while maples, balsam fir, and white pine became more prevalent. We discuss the potential interactive effects of forestry practices, natural disturbances, and climate change on these changes. We conclude that forestry archives are valuable long-term ecological data that should be systematically analyzed to assess global long-term forest change. • Forest landscapes change with forestry, natural disturbances, and climate change. • We analyzed changes from 1950 to 2020 across 3.8 million ha in Canada. • Results showed significant shifts in forest landscape age structure and composition. • Forestry archives are deeply valuable for reconstructing long-term forest dynamics.