Climate change with concomitant increases in global sea temperatures, rising sea levels, and shifts in weather patterns may affect the frequency and intensity of tropical storms. Some recent hurricane-prediction modeling suggests almost a doubling of intense tropical storms by the end of the century; however, overall frequency is expected to decrease. Disturbances associated with hurricanes, such as storm surge and wrack deposition, may play crucial roles in allowing coastal species to migrate inland in response to rising sea levels. An experiment was conducted to examine changes in plant community structure in relation to simulated storm surge and wrack deposition. Vegetation plots were established in four community types (brackish marsh, freshwater marsh, wetland forest, and pine savanna) along an estuarine gradient in northwest Florida. Storm surging consisted of pumping a constant volume of full-strength seawater into flooding enclosures, while experimental wrack was placed atop existing vegetation at a constant depth. Undisturbed control plots with comparable vegetation were also established.  Soil conductivity (µS) was assessed pre- and post-treatment application, as well as light attenuation (PAR) at ground level. Percent cover of each species per plot was determined prior to and after treatment applications.

Results/Conclusions

Post-treatment soil conductivity was significantly higher than pre-treatment values in the wetland forest and pine savanna; however, pre- and post- soil conductivity did not differ in brackish and freshwater marshes. The semi-saline conditions of the brackish marsh and frequent flooding in the freshwater marsh likely contributed to non-significant differences in soil conductivity. In brackish marsh, freshwater marsh, and pine savanna communities, light at ground level was highest for the storm surge treatment, while control and wrack plots had intermediate and low light at ground levels, respectively. The storm surge treatment reduced cover of some species, causing browning and eventual loss of leaves, particularly in pine savanna species. This loss of cover likely contributed to higher levels of light at ground level relative to other treatments. Plant growth in the undisturbed control plots reduced light availability to a lesser degree, while wrack deposits dramatically reduced light levels.  Wrack deposition resulted in substantial mortality to underlying vegetation and reduced species richness in all communities. New recruits into plots with wrack deposits, such as saw palmetto, suggest that these disturbances may facilitate community reassembly. This research should provide insight into how coastal plant communities respond to climate change-related shifts in tropical storm regimes.