Climate change, species loss, and spring phenology in and around Acadia National Park, Maine
McDonough MacKenzie, Caitlin Noel
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Anthropogenic climate change is altering phenology—the timing of biological events, including leafing and flowering—with repercussions for trophic interactions, competition, and species’ persistence. My dissertation aims to uncover, compile, and analyze resources documenting changes in species abundance and phenology in an iconic location (Acadia National Park and surrounding areas) in an understudied region of northern New England. I used the journal of a hunting guide living in Oxbow, Maine in the mid-20th century to document the climate sensitivity of leafing, flowering, and migratory bird arrivals. In Acadia National Park, Maine, I examined changes in the abundance of species by analyzing data from past and contemporary published floras for the park, and published analyses of floristic change from elsewhere in the northeastern United States. I used reciprocal transplants in common gardens and trail-side monitoring across elevation gradients in Acadia to examine inter- and intraspecific variation in plant phenology. Results showed that many native species declined in abundance or disappeared from the flora of Acadia over the past 120 years, similar to changes in floras elsewhere in New England. However, changes in the abundance of particular species in southern New England are not predictive of how they changed in Acadia. Some plant families (e.g. Orchidaceae and Liliaceae) declined disproportionately, but plant vulnerability was not related to habitat preference or range. The phenology of leaf out, flowering and migratory bird arrivals in and around Acadia demonstrate advances in response to warmer temperatures, albeit more slowly than plants in southern New England. Within Acadia, the temperature of local microclimates is a better predictor of plant phenology than elevation or aspect. Local adaption in leaf-out phenology sensitivity was not significant as populations from across a range of elevations responded similarly to different local microclimates in common gardens. This pattern contrasts with other montane systems where high elevation populations displayed reduced phenological sensitivity compared to low elevation populations. The results of this dissertation research underscore the importance of local data and of combining data from multiple sources (historical records, new field observations, and experiments) to describe changes in plant abundance and phenology, to assess species vulnerability, and to support decisions regarding future management and monitoring.