Ghost Forest Rising: A Hyperspectral Approach to Assessing Vegetation Health and Tree Die-Off in Response to Saltwater Intrusion in a Coastal Environment

In coastal areas, saltwater intrusion is a natural occurrence that can affect the quality of groundwater and surface water. Saltwater intrusion can also affect the health of vegetation that depends on fresh water. We studied the effects of saltwater on vegetation with particular focus on loblolly pine trees (Pinus taeda). Our study took place on the Albemarle-Pamlico Peninsula (APP), a 6,000 km2 region of North Carolina's Outer Coastal Plain surrounded on three sides by estuarine coastline. Years of local, anecdotal observations suggest that stands of dead pine trees known as "Ghost Forest," are spreading along coastal waterways. We investigated the health of pine trees in this region to explore potential links between saltwater intrusion and die-off, particularly where artificial ditches and canals allow saltwater to flow deep into the interior of the peninsula. Using a handheld spectroradiometer, we collected hyperspectral reflectance data in visible and near infrared wavebands (350-1000 nm) from more than 100 individual canopy and leaf samples across the APP. We accompanied these measurements with GPS coordinates, measurements of tree height and circumference, distances from nearby waterways, and specific conductance measurements (as a salinity proxy) of these waters. We used reflectance spectra to calculate the Normalized Difference Vegetation Index (NDVI), the Red-Green Index (RGI), and site-specific indices to determine the health of particular trees and canopies. Using this information in conjunction with ancillary data, we explored the correlations between the health of vegetation and the salinity of nearby water sources.