Impacts of Anthropogenic Change on Plant Reproduction and Fitness

Faidiga, Alexandra

ABSTRACT (chapter 2): Phenology is a key trait that can determine survival and reproduction, and thus is crucial to the ultimate fitness of organisms. Shifts in plant phenology in response to rising temperatures are one of the clearest indicators of the effects of recent climatic change. In North America, many species in the New England region are currently flowering earlier in the year relative to historical flowering dates in response to rising spring temperatures. However, comparatively fewer studies have examined phenological shifts in the Southeastern United States, a hotspot of biodiversity in North America. Further, the few existing studies of phenology in the Southeastern US do not account for ecoregional variation, a potentially important predictor in an area characterized by great variation in abiotic conditions over relatively small geographic areas throughout the lower Appalachians. Here, I use 10000+ digitized herbarium records along with associated location-specific temperature data to characterize how the phenologies of 14 common spring-flowering plant species in Eastern Tennessee, a hotspot of biodiversity in the Southeastern US, have responded to warming temperatures over the past century. My results illustrate that, at the community level, plants in different ecoregions differ in their sensitivity to temperature, with plants in the Ridge & Valley ecoregion flowering 2.7 days earlier per degree Celsius warming compared to 1.3 days for plants in the Blue Ridge ecoregion. Additionally, I found that the timing of early flowering at the community level is especially sensitive to spring temperature in both ecoregions. Finally, I show that the majority of spring-flowering species in both ecoregions demonstrated phenological sensitivity of flowering to spring temperature, indicating that in warmer years, the majority of species flowered earlier. Despite the demonstrated sensitivity of communities and species to spring temperature, I did not find support for significant shifts in community flowering within eastern Tennessee in recent decades, likely due to increases in mean annual temperature in the southeast being driven primarily by warming summer (rather than spring) temperatures. These results highlight the importance of including ecoregion as a predictor in phenological models to capture potential variation in temperature sensitivity among populations, and suggest that even small increases in temperature can have dramatic effects on species’ and communities’ phenologies in response to climate in the Southeast.