Investigating the distribution and diversity of rare endemic forest plant species in the eastern United States

Anthropogenic climate change is one of the most pressing issues facing plant species today. Other human activities, such as habitat fragmentation will make it significantly more difficult for plants to migrate poleward and to higher elevation in response to climate change. This may increase the extinction rate as climate warming continues. However, not all species will be affected equally by a warming climate. Species with small-range size and limited dispersal ability face a disproportionately high extinction rate. One way to predict the future of plant species in the face of climate change is studying past climate change and its effects on species. To do this, I studied a group of 206 endemic forest species found in the Temperate Deciduous Biome of the eastern United States. I mapped, analyzed and described patterns of richness in the distribution of the rare endemic forest plant species in the eastern US, focusing on how historical and environmental conditions are associated with distribution patterns today using an ANCOVA. I also examined the different distributions of herbaceous and woody species. I then compared the dispersal modes of the rare plant species with a group of widespread forest species from the Northeast US using Chi-squared tests. I found that small-ranged endemic forest plants were uncommon or absent across the northern US, in the upper Midwest and Northeast, while endemics were common and overlapped in significant hotspots of endemism in the Southeast US. The results of the ANCOVA analysis indicated that glacial history had an overriding effect on biogeographic patterns. The different ANCOVA correlations between environmental variables and endemic richness in the formerly-glaciated north versus the unglaciated south highlight the profound effect glaciation has had on richness of small-ranged endemic species. The ranges of the herbaceous species were, on average, situated closer to the LGM than the woody species though there was no significant difference between the two groups’ range sizes, possibly because herbaceous species can spend the winter underground, and persist in microrefugia, e.g. on the side of a cliff, unlike woody species, and thus could persist closer to the glaciers. When the small-ranged endemics were compared to widespread forest species in the northeastern US, the endemics were found to have a disproportionately high number of local dispersal mechanisms. The implications of this research are troubling for many of the small-ranged, dispersal-limited species included in this study, because these species will likely have difficulty persisting in a rapidly warming climate. However, this research also highlights the importance of protecting climate refugia, because they are relatively stable climatically and may allow species adapted to a cooler, wetter climate to persist as the landscape around these refugia warms due to anthropogenic climate change