Immediate and Long-term Responses of Coastal Vegetation to Extreme Storm Events along the Northern Gulf of Mexico

Abstract

Tropical storms occur frequently along the northern Gulf of Mexico, creating disturbances in coastal areas already influenced by rising seas. Responses of vegetation to extreme storm events at different time scales provide insight into ecosystem resiliency and future persistence. This study examines short- and long-term impacts of 27 extreme storm events on emergent herbaceous wetlands and woody wetlands in southeastern Alabama, USA using Normalized Difference Vegetation Index (NDVI) data. NDVI indicates vegetation vigor and is commonly used to measure responses to disturbance. We hypothesized overall decreases in NDVI, immediately following storm events, and over longer time scales due to cumulative impacts of multiple storms and compressed recovery times. We also expected declining NDVI in emergent herbaceous wetlands following saline storm surges, and in woody wetlands following strong winds. Half of the events (13/27) led to significant immediate declines in NDVI, whereas NDVI increased over the 17-year study period in both wetland types. Fresh water inputs from precipitation and runoff may have contributed to increased NDVI in emergent herbaceous wetlands following disturbances, whereas resprouting in canopy gaps from defoliation and uprooting may have increased NDVI in woody wetlands. An overall increase in NDVI in the last five years of the study period may, in part, reflect migration of some species to more suitable upslope habitat. These results suggest that coastal ecosystems along the northern Gulf of Mexico are more resilient to climate change than previously assumed, particularly where upslope migration is possible.