Intensive land use activities, such as agriculture, are a leading cause of biodiversity loss and can have lasting impacts on ecological systems. Yet, few studies have investigated how land-use legacies impact phylogenetic diversity (the total amount of evolutionary history in a community) or how restoration activities might mitigate legacy effects on biodiversity. We studied ground-layer plant communities in 27 pairs of Remnant (no agricultural history) and Post-agricultural (agriculture abandoned >60 years ago) longleaf pine savannas, half of which we restored by thinning trees to reinstate open savanna conditions.
We found that agricultural history had no impact on species richness, but did alter community composition and reduce phylogenetic diversity by 566 million years per 0.1 ha. This loss of phylogenetic diversity in post-agricultural savannas was due to, in part, a reduction in the average evolutionary distance between pairs of closely related species, that is, increased phylogenetic clustering. Habitat restoration increased species richness by 27% and phylogenetic diversity by 914 million years but did not overcome the effects of agricultural land use on community composition and phylogenetic clustering. These results demonstrate the persistence of agricultural legacies, even in the face of intensive restoration efforts, and the importance of considering biodiversity broadly when evaluating human impacts on ecosystems.