Determinants of tree plantation establishment success in agricultural gullies under operational conditions: A large-scale multi-site study in southern Québec, Canada

Agricultural gullies are characterized by steep slopes, strong herbaceous competition, and frequently poor drainage, which represent highly constrained environments for tree establishment. This study was conducted across 25 sites in southern Québec (Canada), evaluating establishment success of young plantations (< 10 years) under operational conditions. It quantified effects of abiotic factors (topography, soil physicochemical properties), biotic factors (volunteer vegetation, herbivory), and management practices (mowing, mulching, herbivore protection devices, planting season) on tree survival and growth. Mean survival reached 73%, comparable to a level attained under more favourable agricultural afforestation contexts. Contrary to expectation, broadleaf and conifer species exhibited similar survival. Tree survival increased with increasing abundance of naturally regenerated shrubs; while the presence of planted shrubs promoted growth in some species, suggesting facilitative effects likely mediated by microclimatic buffering and reduced herbivory. Among management practices, mowing of herbaceous vegetation greatly benefited both tree survival and growth, likely through reduced competition. Herbivore protection devices also enhanced growth, although no significant effect on survival was detected. At the site scale, growth decreased with increasing slope inclination, confirming the limiting role of topographic constraints. In contrast, edaphic properties (texture, pH, drainage) had limited overall effects, likely due to low variability among sites. Conifers and pioneer broadleaf species (poplars and birches) exhibited higher growth than other groups, highlighting the importance of species selection in these environments. Overall, this study highlights key ecological and management drivers of plantation success in constrained and abandoned agricultural landscapes, providing guidance for improving afforestation practices.