Using remote sensing to detect long-term coastal plant community changes due to sea level rise and ecosystem drying, Everglades National Park

Background/Question/Methods: Increasing sea levels and anthropogenic alterations are resulting in changes in or complete loss of coastal plant communities around the world. In combination with sea level rise (SLR), the Everglades ecosystem has undergone large-scale drainage and restoration changing coastal vegetation throughout south Florida as saltwater-loving communities move into freshwater wetlands and uplands. We asked have plant community shifts occurred along the southern coast of Everglades National Park (ENP) between 1978 and 2011? Specifically, whether the spatial extent and distribution of coastal plant communities has transitioned from less salt- and inundation-tolerant to more salt- and inundation-tolerant communities over the 33-year period. We utilized remote-sensing techniques to create a map of coastal plant communities in 2011 and compared it to one made from 1978 aerial imagery. For the 2011 map we used bi-seasonal WorldView-2 2x2m satellite imagery flown at the end of the wet (December 2011) and dry (April 2013) seasons and a supervised random forest algorithm to classify seven plant community types.

Results/Conclusions: We found that lowland plant communities moved up the coastal elevation gradient, changing from less salt- and inundation-tolerant to more salt- and inundation-tolerant communities. White mangrove forest decreased 16% and black and red mangrove forests increased 27 and 11%, respectively, suggesting the area became saltier and wetter. Additionally, the two highest-elevation communities, tropical hardwood hammock and buttonwood forest, decreased by 4 and 6%, respectively.

Our map shows that in 2011, the ENP coastal communities were still quite diverse, maintaining a complex matrix of black and red mangrove forests, halophyte prairie, two buttonwood communities (glycophyte and halophyte), white mangrove forest, and tropical hardwood hammock. However, if the losses in upland communities seen between 1978 and 2011 continue, there will be a decrease in species and community diversity along the ENP coast, as tropical hardwood hammocks and buttonwood forests disappear. Upland coastal plant communities in ENP maintain 21 rare plant species that are threatened by SLR, including the federally endangered plant Chromolaena frustrata (Saha et al. 2011). Further shrinking in cover of the habitats that support these rare species increases threats to them; some may become extirpated or extinct (Saha et al. 2011).  If we want to preserve biodiversity and ecosystem integrity, the effects of SLR and Everglades drying on coastal south Florida should be addressed immediately.