2018 ESA Annual Meeting (August 5 -- 10)

COS 71-6 - Succession, regression and loss: recent changes in tree community composition on North Carolina’s coastal plain

Wednesday, August 8, 2018: 9:50 AM
235-236, New Orleans Ernest N. Morial Convention Center
Emily Ury, Steve Anderson, Emily Bernhardt and Justin P. Wright, Biology, Duke University, Durham, NC
Background/Question/Methods

Coastal plain plant communities are considered to be highly vulnerable to future sea level rise, but it is unknown the extent to which they have already been impacted by saltwater intrusion. We examined freshwater, forested wetlands across the Albemarle-Pamlico Peninsula in North Carolina. Most of these lands are in early stages of natural succession or restoration from previous uses in forestry or agricultural. We conducted surveys in 34 mature forest stands across the region; a subset of these plots (16) were part of the Carolina Vegetation Survey during the previous decade. Across the 2016 survey we asked what are the primary drivers shaping current tree community composition? For the subset of resampled plots we were also able to ask whether changes in biomass or composition were related to soil salinity? We hypothesized that tree community composition change will correspond with plot vulnerability to climate change. The change predictors we measured include elevation, as a proxy for vulnerability to sea level rise, and soil chloride/sulfate concentrations as an indication of salinization. Ordination was used to evaluate tree community composition change between the two survey periods and linear regression models to assess the predictive strength of environmental drivers.

Results/Conclusions

Our analysis shows that climate change predictors explain both current tree community composition and compositional changes over time. An NMDS cluster analysis of tree community composition identified four main community types: cypress swamps, pond pine/bay woodlands, cedar swamps, and mesic mixed hardwood forests. These community types sort along the region’s shallow elevation gradient (all plots are less than 4 meters above sea level). The most vulnerable community types in this region are the cedar swamps and the pond pine/bay woodlands due to their natural positioning in the lowest parts of the landscape. In addition to changing community composition within these plot types, the change analysis also demonstrates that vulnerable plots may suffer from impaired tree growth and even loss of total tree biomass (61% loss in the cedar swamp). Change in plot total basal area is tightly correlated with log(elevation) for the 16 plots surveyed at two time points (R2 = 0.799). These findings have implications for future management of coastal wetlands to ensure conservation efforts are effective in the midst of global change.