Jackson, Michelle M. 2012. Influence of climate and logging history on native forest herbs and their pollinators in the southern Appalachians. PhD dissertation, University of Wisconsin-Madison.

The conservation of biodiversity in the face of global change requires understanding the interactions among multiple drivers.  Climate change is a pressing global issue that will likely interact with land-use history and other drivers to alter ecosystems in novel ways that are difficult to predict.  Additionally, the importance of land use legacies in forests is being 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.  I investigated the interacting effects of logging history and climate on forest herbs and their pollinators in the southern Appalachian region of western North Carolina, USA.  Using presence-absence data for 14 species of forest herbs, I developed a novel multilevel modeling (MLM) approach for analyzing the effects of environmental variables on species distributions and community composition simultaneously.  I use simulated data to show that MLMs can outperform three standard methods commonly used to identify environmental drivers of the species composition of communities: redundancy analysis (RDA), canonical correspondence analysis (CCA), and nonmetric multidimensional scaling (NMDS).  Field measurements and a seed sowing experiment were then used to examine how plant performance of four focal species of forest herbs 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 a three-year time period, which included years with strikingly different patterns of precipitation.  Stage-based matrix models and life table response experiments were used to quantify the demographic contributions to observed differences in population growth rates for one focal species, Prosartes lanuginosa, across stands and years.  Lastly, I surveyed the pollinator community along gradients of stand age, elevation, and distance to logging roads and used the MLM approach to investigate the effects of these drivers on pollinators at the family and community-level.  Populations of focal herb species in recently logged stands showed evidence of reduced performance, with lower recruitment, higher within-plot variation in recruitment density, 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 were different across stand age, being driven primarily by reduced fecundity in old stands and by reduced growth from vegetative to flowering life stages in young stands.  Many important pollinator families were found in higher abundance in recently logged stands and close to roads, especially in summer when logging roads provide supplemental light and floral resources for insects, but the beneficial effects of roads on the bee community appeared to diminish as forests matured.  Overall, this work provides valuable insights regarding the roles of logging history and climate in shaping the current and future trajectories of native understory herbs and pollinating insects in the Southern Appalachians.