Climate and sea level rise driven forest mortality along the Southeastern and Gulf coasts of the US

Marcelo Ardon, Forestry and Environmental Resources, North Carolina State University, Raleigh, NC, Kevin M. Potter, Department of Forestry and Environmental Resources, North Carolina State University, Research Triangle Park, NC, Elliott White, Environmental Science, University of Virginia, Charlottesville, VA and Christopher W. Woodall, Northern Research Station, USDA Forest Service, Durham, NH

Background/Question/Methods
Increased flooding, saltwater intrusion due to sea level rise and increased human appropriations of groundwater, and wind damage due to storms are all affecting forests along the Southeast and Gulf coasts of the US. However, we still lack a clear understanding of the magnitude of these effects on forests in this region. Here we used data from the Forest Inventory Analyses (FIA) program to quantify the effects of sea level rise and storms on forests along the Southeast and Gulf coasts. We asked: 1) are coastal (low elevation) plots similar in structure to upland (mid elevation) plots with similar physiography? 2) what are the stocks of recent standing and downed dead carbon (C) in low and mid elevation plots? We hypothesized that while the forest structure of low and mid elevation plots would be similar, the low elevation plots would have higher stocks of dead C, due to the influences of sea level rise and storms. We identified data from low elevation (≤5 m, n= 923) and mid elevation plots (around 50 m, n= 953) from the last FIA survey (trees were sampled between 2012-2016). The dataset included measurements for more than 34,000 trees.

Results/Conclusions
We found that low and mid elevation plots had similar numbers of species (mean ± standard deviation = 37 ± 21 low, and 35± 19 mid elevation), live (0.14 vs 0.15 trees m-2 for low and mid elevation plots, respectively), and dead trees (0.016 and 0.015 dead trees m-2 for low and mid elevation, respectively). However, low elevation plots had approximately 37% more recent standing dead C (0.66 kg C m-2 low vs 0.48 kg C m-2) and 94% more downed C (0.72 kg C m-2 vs 0.37 kg C m-2). We identified areas with high standing dead C near the Louisiana, North Carolina, South Carolina, and Maryland coast. We also found a 58% decrease in growth of loblolly pine in low elevation plots, which could cause losses of revenue to landowners. Our results suggest that sea level rise and storms are already affecting coastal forests and causing widespread mortality and decreased growth of trees.