Climate change is redistributing species around the globe, and one consequence is a tropicalization of temperate ecosystems. In coastal wetlands along the east coast of North America, there have been observations of mangroves expanding into salt marshes near the current poleward range limit of mangroves in northeast Florida. However, there is currently a debate over whether these changes are a response to anthropogenic climate change (ACC), or are simply reemergences of mangroves in response to decadal-scale oscillations in climate.
We used satellite imagery, aerial photos, historical shoreline maps from the USGS, and other historical records to document changes in mangrove abundance along the northeast coast of Florida from the late 1700s to the present. These changes in the mangrove-salt marsh ecotone were compared to climate variability over the past 150 years. We then used modeled climate projections to estimate the contribution of ACC to observed decreases in the frequency of extreme freeze events. We also projected how the frequency of freeze events in this region will change over the next 50 years.
Results/Conclusions
We found that coastal wetlands in northeast Florida shifted between mangrove and saltmarsh dominance a number of times over this period. Shifts towards saltmarsh dominance were relatively rapid and linked to extreme freeze events, while shifts towards mangrove dominance occurred during extended periods of milder winters. Our results suggest that the recent mangrove range expansions should indeed be placed into a broader historical context of an oscillating system. However, this recent expansion may be different than previous ones as climate modeling suggests that ACC is causing a more permanent shift towards mangrove dominance in this region.