Low-lying coastal wetlands will likely be affected first and most intensely by the consequences of continued global climate change, especially changing patterns of sea level rise and hurricane activity.In these dynamic environments, such disturbances are commonplace, but recently disturbed ecosystems may be less resilient to subsequent disturbance. Increasing hurricane frequency and intensity, may overwhelm the adaptive capabilities of coastal wetlands, resulting in dramatic losses of biodiversity and essential ecosystem services over the next century. To better understand the effects of changing disturbance regimes, we studied long-term responses of wetland habitats to hurricane activity along a coastal transition in the northern Gulf of Mexico, USA. A research transect was established in Jean Lafitte National Historical Park and Preserve (Jefferson Parish, LA), atop a naturally-occurring elevation gradient. Woody vegetation along this transect was sampled in 2005 (pre-Hurricane Katrina), 2006 (post-Katrina), and 2017 (12 years post-Katrina). We monitored direct effects of wind damage on the ecotone region, or the interface between fresh water swamp and levee forest habitats. Species richness and total abundance of individuals were sampled within 10x10m plots (replicates) for swamp and forest habitats and changes over time were then compared across three vegetation strata (understory, subcanopy, and canopy). We hypothesized that hurricane wind damage would have no significant effect on the biodiversity of woody vegetation within these coastal wetland habitats over time. We reasoned that biodiversity would change very little as post-disturbance succession would be driven by the species present just before the hurricane’s passage, according to the direct regeneration hypothesis.
Results/Conclusions
Wetland habitats along this coastal transition have not returned to pre-hurricane levels of woody vegetation biodiversity. The effects of habitat type were non-significant at the p<0.05 level for both response variables (richness and abundance). The canopy (>20m) and understory (<10m) strata displayed significant decreases in richness and abundance with time. However, the opposite trend was observed in the subcanopy (10-20m) stratum for both response variables. The observed thinning of the canopy in both habitats does not follow the patterns of direct regeneration by primary species that has been documented in other forests following hurricane wind damage.This trend may be exacerbated in the future, even under moderate projections of global climate change and sea level rise. Further investigation into the mechanisms underlying these long-term shifts in vegetative structure will be needed to help determine whether wetland habitats along coastal transitions will persist in the face of global change.