Land-use legacy drives post-abandonment forest structure and understory in the western Alps

• Forest expansion is the main land-use transition in a landscape of the western Alps. • Legacy of grasslands and wooded areas affect post-abandonment forests differently. • Post-abandonment forest overstory and understory depends on historical land-use. • Land-use legacy is a key factor for understanding post-abandonment forest landscapes. Rural exodus from European mountain regions to lowlands has triggered natural reforestation of abandoned lands in the 19 th and 20 th centuries, altering the provision of ecosystem services and creating management challenges. Post-abandonment forests are complex ecosystems that respond over time and space to several drivers. Their management requires integrated approaches that involve insights from historical ecology. Our study aimed to assess the influences of the land-use legacies on post-abandonment forest overstory and understory and provide insights on suitable management strategies. We assessed these influences using multiple scales (from landscape to field scale) and ecological approaches (vegetation, forest, and landscape ecology). We identified post-abandonment forests within a western Alps watershed through a land-use/land-cover change detection from 1954 to 2017. Field surveys were conducted in three different land-use legacy types (i.e., transitions from former grasslands, wood-pastures, and sparse forests to dense forests) to analyse forest overstory and understory. We explored the influences of land-use legacy on post-abandonment forests through redundancy analysis, using forest overstory and understory variables as response variables and environmental factors as predictors. Our study revealed successional and environmental differences among post-abandonment forests, notably depending on the historical presence of biological legacies: forests originating from former wooded areas exhibited ecological conditions closer to natural trajectories, while those resulting from abandoned grasslands still express conditions similar to the pre-abandonment ones. Based on our findings, we discuss how the direct implications of land-use legacies on post-abandonment forests can provide insights into their management.