Post-agricultural forests: Landscape patterns add to stand-scale factors in causing insufficient hardwood regeneration

Abstract

Over the last century, the northeastern United States and eastern Canada have witnessed gradual abandonment of unproductive agricultural land types. This major shift in land-use management has released numerous sites, which are now dominated by early-successional forests. Continued anthropogenic disturbance and isolation of these plant communities within an agricultural mosaic should compromise their natural regeneration, but few studies have addressed these issues. We sampled 28 former farmlands that were within 3 agroforested landscapes in southwestern Quebec (Canada) and which were characterised by a closed canopy of pioneer tree species. We measured regeneration of valuable hardwoods to quantify the relative effects of stand factors and landscape patterns on that regeneration. Our results suggest that the persistence of high-value forests in such agricultural landscapes is jeopardised, due to a problem of recovery for hardwoods at the stand scale. Diversity and abundance of tree seedlings was low; 56.5% of the plots contained no valuable hardwood regeneration >30 cm in height. Furthermore, only 10.9% of all plots contained more than one valuable species. GIS and multivariate analyses revealed two distinct successional alternatives, which varied with the degree of agricultural footprint of the stand and landscape. Only one path led to valuable hardwood forests, although with very few valuable species. Regeneration was insufficient when seedling availability from nearby forest patches was limited, but it was enhanced under particular soil conditions and structure of stands, which could help guide management practices in these ecosystems.