Patterns of species loss and spring phenology in the plant communities of Acadia National Park, Maine

Background/Question/Methods:

Warming temperatures in temperate northeast North America have led to advances in spring plant phenology. However, plants differ in their phenological responses to warming depending on taxa, population, habitat, and/or geographic location. Phenology is a key plant trait included in many climate change vulnerability assessments, but its use in these assessments has not been rigorously evaluated, in part because researchers need a better understanding of the environmental controls on phenology at a species level. We take an interdisciplinary approach to this problem by merging historical ecology, observational and experimental fieldwork, and citizen science in Acadia National Park. We use historical data to record patterns in species loss in Acadia over the past 120 years. We are monitoring leaf out and flowering across elevations along transects to quantify the relationship between spring temperatures and shifts in phenology at the species level for a community of thirty common species. We are also applying a regional comparison of phenology and species loss for conspecific populations in Acadia versus Concord, Massachusetts. Finally, we installed three reciprocal transplant gardens at three elevations in Acadia to test the relative effects of environmental cues and genetic differences at the population level on spring phenology for three understory plant species.

Results/Conclusions:

Acadia has lost 21% of the plant species historically recorded in surveys from 1894, 1908, and 1929, while an additional 32% of the flora has declined in abundance since 1894. Concord, Massachusetts has lost 27% of the flora since Thoreau’s time (1850s); however, a comparison of conspecific populations reveals that nearly 70% of taxa are experiencing divergent trends in abundance between Concord and Acadia. Preliminary results from a subset of transect species monitored in Acadia in 2013 and 2014 show that spring phenology is responsive to year-to-year variation in climate and local microclimates (based on elevation and aspect). We are expanding the transect monitoring by creating a citizen science opportunity for hikers visiting the park and will be designing and testing protocols in 2015. After one season, we found that the microclimate at each transplant garden is the dominant cue for leaf out phenology, though there may be some local adaptations for temperature-sensitivity among the source populations. It is possible that the influence of source population is a lingering environmental effect of where the plants were growing before Year 1; additional field seasons will allow us to refine this hypothesis and add flowering phenology to our garden observations.