Coastal forests in the Mid-Atlantic region are threatened by sea level rise through chronic and episodic salinization and hydrologic alterations, leading to inland marsh migration and the occurrence of ghost forests. This study uses dendrochronology to explore the impact of rising sea level on the annual growth of Juniperus virginiana (the Eastern red cedar) at the St. Jones component of the Delaware National Estuarine Research Reserve in Dover, DE. Chronologies from low and high elevations were developed, and a difference chronology (high–low) was generated. A rapid field assessment of tree stress indicated greater stress in low elevation trees, and low elevation soil tests showed higher soil moisture and salt content compared to samples from high elevation. Ring width indices were analyzed in relation to water level, precipitation, the Standardized Precipitation Evapotranspiration Index, and temperature, with Pearson’s correlation analysis. Trees growing at low elevation showed greater climate sensitivity and responded favorably to cool, wet summers. Over time, correlations between growth and climate variables decreased, while negative correlations with tidal water level increased—a pattern that presented nearly a decade earlier in the low elevation system. Given the widespread distribution of the Eastern red cedar and its sensitivity to changes in sea level, this species may be particularly useful as a sentinel of change in coastal landscapes as sea levels rise.

Flood frequencies in coastal forests are increasing as sea level rise accelerates from 3–4 mm year⁻¹ to possibly more than 10 mm year⁻¹ by the end of this century. As flooding increases, coastal forests retreat, ghost forests form, and coastal marshes migrate inland. The existence of ghost forests makes the mechanism of forest retreat clear: low-lying trees become more exposed to coastal flooding until they ultimately die. Variability in these retreat rates, however, makes it difficult to predict where and when retreat will continue to occur. Understanding tree growth responses to tidal water levels relative to other environmental factors is a critical step in elucidating the factors that influence retreat variability. Here, dendrochronology was used to study factors that contribute to variations in growth patterns in four coastal forests fringing the Delaware and Barnegat Bays. Species chosen for study included loblolly pine (Pinus taeda), pitch pine (Pinus rigida), and American holly (Ilex opaca). Pearson’s and partial correlation tests showed that growth relationships with monthly environmental conditions varied across sites and were moderate in strength (generally R < 0.5), but each site had at least one significant growth-water level correlation. As coastal flooding exposure is spatially dependent, tree chronologies were also separated into high and low elevation groups. Pearson’s and partial correlation tests of the mean differences between elevation groups showed that at some sites, low elevation trees grew less than high elevation trees when water levels were high, as might be expected. At one site, however, lower elevation trees grew more when water levels were higher, which suggests that other interacting factors—regardless of current flood exposure—potentially have positive, yet likely temporary, influence over tree growth in these low-lying areas.

The placement of dredged sediment on salt marshes, often termed “thin layer placement” (TLP), is a promising strategy to offset elevation loss and combat marsh degradation. However, inconsistent terminology, reporting practices, and lack of standardized quantitative success criteria hinder synthesis and guidance development. To address these gaps, we reviewed 89 TLP-related papers, reports, and other documents to evaluate reporting conventions and identify opportunities for standardization. Our analysis revealed substantial variability in methodology and reporting, limiting cross-project comparisons and other meta-analysis. For example, 57% and 50% of projects did not report initial marsh elevations or tidal range, respectively, which are metrics critical for interpreting flood frequency and elevation targets. Few projects clearly stated quantitative goals or success criteria, often relying on generalized objectives such as “ecological uplift,” which provide little insight into design applicability. Regional differences in placement thickness further complicate comparisons, as ecological conditions and sediment availability vary widely. Based on these findings, eight recommendations were proposed to improve clarity and comparability: (1) explicitly report project goals and link them to monitoring metrics; (2) define success criteria; (3) use consistent terminology referencing sediment placement; (4) report placement depth, range, and initial elevations; (5) include local tidal range and datum; (6) clarify controls versus references; (7) consider longer monitoring timeframes; and (8) share comprehensive results beyond peer-reviewed summaries. Adoption of these practices will enhance transparency, facilitate meta-analysis, and support evidence-based design and evaluation of future TLP projects.

Digital elevation models (DEMs) based on LiDAR surveys provide critical information for predicting the vulnerability of coastal areas to sea-level rises. Due to the poor penetration of LiDAR pulses in marsh vegetation, bare-earth DEMs for coastal wetlands are often subject to positive elevation bias, and thus underestimate vulnerability. This data publication includes comprehensive elevation surveys from seven coastal wetlands in coastal New Jersey, and an evaluation of the accuracy and positive elevation bias of each publically available DEM. Resampling the DEMs at a coarser resolution, replacing cell values using the minimum value in a wider search window (4 m), removed this positive elevation bias with no loss of accuracy.

Tidal marshes protect coastal communities from the effects of sea level rise and storms, yet they are vulnerable to prolonged inundation and submergence. Uncertainty regarding their vulnerability to sea level rise motivated the establishment of a monitoring network in the Delaware Estuary and Barnegat Bay. Using data collected through these efforts, we determined whether rates of tidal marsh sediment accumulation and elevation change exceeded local sea level rise and how these dynamics varied along geographic and environmental gradients. Marker horizons, surface elevation tables, elevation surveys, water level data, and water column suspended sediment concentrations were used to evaluate sea level rise vulnerability. Of 32 study sites, 75% had elevation change that did not keep pace with long-term rising sea levels (1969–2018) and 94% did not keep pace with recent sea level rise (2000–2018). Mean high water rose most rapidly in the freshwater tidal portion of the Delaware Estuary with rates nearing 1 cm yr^-1 from 2000–2018. We noted that greater sediment accumulation rates occurred in marshes with large tidal ranges, low elevations, and high water column suspended sediment concentrations. We found correlations between rates of shallow subsidence, increasing salinity, and decreasing tidal range. Marsh elevation and water level surveys revealed significant variability in elevation capital and summer flooding patterns (12–67% inundation). However, rapid increases in mean high water over the past 19 years suggests that all marsh platforms currently sit at or below mean high water. Overall, these data suggest that tidal marshes in the Delaware Estuary and Barnegat Bay are vulnerable to submergence by current rates of sea-level rise. While we observed variability in marsh elevation capital, the absence of strong correlations between elevation trends and environmental parameters makes it difficult to identify clear patterns of sea level rise vulnerability among wetlands.