Pasture trees contribute to structural heterogeneity and plant distributions in post-agricultural forests decades after canopy closure
Holmes, Marion (2020), Pasture trees contribute to structural heterogeneity and plant distributions in post-agricultural forests decades after canopy closure, Dryad, Dataset, https://doi.org/10.5061/dryad.x0k6djhg2
Questions: Open-grown shade trees retained in pastures are legacies of agricultural history that influence recolonization dynamics and create structural heterogeneity in post-agricultural forests. This work addresses the long-term influence of pasture trees on forest structure and composition. I ask: Do signs of successional nucleation in microhabitat, structure and composition near pasture trees persist decades after canopy closure? If so, does variation primarily reflect seed deposition or environmental facilitation?
Location: Southeastern Ohio, USA
Methods: Thirteen open-grown trees greater than 70 cm in diameter in second-growth forests 40-90 years old were selected as study sites. Trees, saplings, herbs, and environmental variables were sampled and compared at three positions around each tree: under the canopy, at the dripline, and in the forest matrix.
Results: Soil pH was lower and coarse woody debris most abundant under pasture tree canopies. Stems >10 cm in diameter at breast height were nearly absent under each focal tree’s canopy and most abundant at its dripline. Composition under the canopy was limited to shade-tolerant trees, whereas the dripline was characterized by vertebrate-dispersed species. Ant-dispersed, adhesive, and unassisted herb species were most abundant under embedded pasture trees compared with the forest matrix.
Discussion: Evidence of nucleation around open-grown trees persists for decades after canopy closure. Contrasts in structure and composition reflect spatially segregated interactions of competitive suppression and facilitation mediated by both dispersal and environment. Pasture trees contribute variation in microhabitat, composition, and structure to post-agricultural forests, and their retention should be encouraged.