Shifts in flowering phenology in response to spring temperatures in eastern Tennessee

Plant phenological shifts are among the clearest indicators of the effects of climate change. In North America, numerous studies in New England have demonstrated earlier spring flowering compared to historical records. However, few studies have examined phenological shifts in the southeastern United States, a highly biodiverse region of North America characterized by dramatic variation in abiotic conditions over small geographic areas. Here, we use 1000+ digitized herbarium records along with location-specific temperature data to examine phenological shifts of 14 spring-flowering species in two adjacent ecoregions in eastern Tennessee. We show that spring-flowering plant communities in the Blue Ridge and Ridge & Valley ecoregions differ in their sensitivity to temperature; plants in the Ridge & Valley flower 2.7 days earlier/ºC on average compared to 1.3 days/ºC for plants in the Blue Ridge. Additionally, we show that for the majority of species in both ecoregions, flowering is sensitive to spring temperature; i.e., in warmer years, most species flowered earlier. Despite this sensitivity, we did not find support for community-level shifts in flowering within eastern Tennessee in recent decades, likely because increases in annual temperature in the southeast are driven primarily by warming summer (rather than spring) temperatures. These results highlight the importance of including ecoregion as a predictor in phenological models for capturing variation in sensitivity among populations and suggest that even small shifts in temperature can have dramatic effects on phenology in response to climate in the southeastern United States.See README.md for descriptions of data structures and sharing/access information