Revealing the Impact of Sea Level Rise on Coastal Forest Structure in the U.S. Mid-Atlantic Using Lidar

Abstract

Global vegetation regimes are undergoing notable changes from the effects of climate change. Coastal ecosystems, in particular are undergoing extensive shifts largely due to the compounding effects of sea level rise (SLR) and intense storm surges, with the Eastern coast of North America experiencing accelerated impacts due to land subsidence and the weakening of the Gulf Stream. The interplay of SLR, land subsidence, and weakened Gulf Stream exacerbates these impacts, altering the zonation from salt-tolerant marshes to upland forests. As tidal flooding increases and extends into the upland forest, elevated water and salinity levels trigger changes in ecosystem function, leading to gradual forest mortality and conversion to marshes, known as coastal transgression. However, understanding how increased tidal flooding affects forest structure and its regional variability remains limited. By leveraging lidar technology from air, land, and space, this dissertation investigates changes in low-lying forest structure induced by SLR and coastal storms, comprising three complementary studies focused on the Delaware Bay Estuary and the broader U.S. Mid-Atlantic region. First, I used multi-temporal airborne Lidar data and high-resolution imagery classify areas of rapid forest loss likely driven from episodic events in the along the Delaware Bay coast. Next, I investigated these areas of forest dieback using ground-based terrestrial laser scanning (TLS) to examine the subtle changes in forest vertical stratification from initial degradation associated with due to inundation. Lastly, I used spaceborne lidar observations to assesses the impact and extent of tidal flooding impact on forest vertical structure across the Mid-Atlantic. These studies revealed variable responses in forest structure along the forest-marsh ecotone to not only improve the delineation of the migrating forest boundary, but to also quantify the extent of degradation linked to inundation, highlighting the roles of topography and tidal influence in facilitating or resisting forest conversion into marshes. The findings of this dissertation accentuate the importance of monitoring forest structural dynamics to detect early signs of upland marsh expansion, essential for assessing changes to the overall coastal carbon sink, which underpins effective natural resource management and restoration efforts.