Influence of climate and logging history on native forest herbs and their pollinators in the southern Appalachians

The importance of land use legacies in forests is increasingly recognized in the context of ecology and conservation, particularly as old growth forests become relegated to smaller, more isolated patches in North America and Europe. Additionally, climate change will likely interact with land-use history to alter ecosystems in novel ways. I investigated the effects of logging history and climate on forest herbs and pollinators in the southern Appalachian region of North Carolina, USA. Using presence-absence data for 14 forest herb species, I developed a multilevel modeling approach for analyzing the effects of environmental variables on individual species and community composition simultaneously. Field measurements and a seed-sowing experiment were then used to examine how performance of four herb species differed between old (logged > 100 years prior to the study) and young (logged 20-40 years prior to the study) forest stands along an elevation gradient over three years. Stage-based matrix models and life table response experiments were used to quantify demographic contributions to observed differences in population growth rates for Prosartes lanuginosa across stands and years. Lastly, I surveyed insect pollinators along gradients of stand age, elevation, and distance to logging roads and used multilevel models to investigate the effects of these drivers on pollinator abundance and composition. Herb species in recently logged stands showed evidence of reduced performance, with lower recruitment, higher within-plot variation in recruitment, greater mortality, and greater proportional biomass allocation to leaves versus stem than in old stands. Population growth rates for P. lanuginosa were lower in young stands and following a drought spring. The demographic mechanisms underlying population responses to drought primarily included reduced fecundity in old stands and reduced growth from vegetative to flowering stages in young stands. Several important pollinator families were more abundant in recently logged stands and close to logging roads, especially in summer when roads represented the primary canopy gap, but the effects of roads on bees appeared to diminish as forests matured. Overall, this work provides valuable insights into the roles of logging and climate in shaping current and future trajectories of understory herbs and pollinators in the Southern Appalachians.