Coastal floodplain forests that occur at the southernmost extent of the great bottomland hardwood forest expanse of the Lower Mississippi Alluvial Valley are undergoing rapid relative sea level rise with chronic increases in flooding. We hypothesized that species would be asynchronous in their responses to these changes; further, we expected that flood-tolerant species would have slower mortality rates and slower upslope rates of establishment than flood-intolerant species. We used long-term data (1998-2015) collected from a 5 ha plot spanning the elevation gradient from the natural levee to the backswamp of Bayou des Familles at Jean Lafitte National Park, Jefferson Parish, LA. The plot was established to track tree distributions, forest regeneration, growth, mortality, and community composition over time.
Results/Conclusions
We found that tree mortality far exceeded regeneration and that major tropical storm events exacerbated these patterns. Sapling distributions indicated upslope migration of several species, while the most flood-intolerant species (Quercus virginiana) exhibited complete regeneration failure. The most flood-tolerant species (Taxodium distichum) had the lowest mortality and did not exhibit upslope shifts. Our results indicate that this forest is rapidly disassembling with the chronic effects of relative sea level rise. However, responses are species-specific and asynchronous. We anticipate survival of the most flood-tolerant species for some time but eventual invasion of marsh with loss of forest canopy.