At range edges, disturbances may alter community composition by facilitating or inhibiting the dominance of one species over another. Therefore, the relative vulnerability of species within ecotones to disturbance will influence community composition after disturbance events. We evaluated the response of a subtropical coastal wetland to an extreme event using a unique dataset on hurricane damage as a function of mangrove cover within the salt marsh-mangrove ecotone. At the mangrove range edge, including the Texas Gulf Coast (USA), mangroves often have a short scrub morphology. The acute and long-term resilience of scrub mangroves within these transitional areas following natural extreme disturbance events is poorly understood. Hurricane Harvey provided a unique opportunity to investigate these dynamics. Harvey came ashore near Port Aransas, Texas as a Category 4 storm in August 2017, passing directly over a black mangrove (Avicennia germinans) experiment that we had initiated in 2012. The experiment consists of ten large (1008 m2) plots ranging from 0-100% mangrove cover, creating a variable mangrove-marsh mosaic that is typical of the community composition at the mangrove range edge. We compared mangrove and marsh plant cover, height, and light attenuation to values measured prior to storm landfall.
Results/Conclusions
Marsh plants were fairly resistant to hurricane effects; post-storm percent cover was similar to or higher than pre-storm levels for most marsh species. Wind damage caused up to 25% loss in mangrove cover, particularly for plots with more than 50% initial mangrove cover. Similar patterns were observed for light attenuation and mangrove height. Wind damage was particularly pronounced on the upper branches of mangroves that were not inundated by the >1.5 m storm surge. Evidence of mangrove regrowth was apparent within two months of landfall. Cover reached 80% of pre-storm values within one year. However, plots with more than 50% initial mangrove cover continued to have lower cover and light attenuation two years after the storm, suggesting that denser stands were slower to recover from storm damage. Although hurricane damage within scrub mangrove stands was not as severe as damage typically observed in tropical mangrove forests, our results indicate that hurricane impacts persisted over multiple growing seasons. The relatively slow recovery of the scrub mangrove ecosystem from a major disturbance event may alter the trajectory and rate of mangrove encroachment.