The capacity of wetlands to stabilize shorelines and reduce erosion is a critical coastal ecosystem service. Gulf of Mexico coastal wetlands are transitional from marshes – dominated by low-stature grass and forb species – to mangroves. Does the taller, woody mangrove vegetation provide different – or better – shoreline protection than salt marsh vegetation during major storm events? Hurricane Harvey provided a unique opportunity to address this question. Harvey came ashore near Port Aransas, Texas as a Category 4 storm in August 2017, passing directly over a mangrove removal experiment that we had initiated in 2012. The experiment consists of ten large (1008 m2) plots ranging from 0-100% mangrove cover, allowing a direct comparison of shoreline protection provided by mangrove and marsh vegetation during the hurricane event. We compared plant cover, shoreline topography, and soil characteristics to values measured prior to storm landfall.
Results/Conclusions
Relative mangrove cover decreased 25-40% after the storm, regardless of initial cover, whereas marsh plants were fairly resistant to hurricane effects. Mangrove damage was particularly pronounced on trees that were more than 1.5 meters tall; the upper parts of the tree were not inundated by storm surge and were impacted by wind and debris. Evidence of regrowth was apparent within two months of landfall; longer term recovery trajectories are uncertain. There was substantial erosion in study plots with less than 33% mangrove cover, up to three times more than the amount in the years preceding the storm. However, within patches of marsh vegetation, there was 2x more accretion above feldspar markers than within mangrove patches. Mangrove cover did not affect the amount or distribution of debris deposited in the study area. In general, mangroves reduced shoreline erosion, but they were also more damaged by wind and surge, which may reduce the capacity of mangroves to protect the shoreline on a longer time scale.