DENDROECOLOGICALLY UNDERSTANDING CHAMAECYPARIS THYOIDES RESILIENCY TO SALINITY INTRUSION

Of Delaware’s 11,000 acres of freshwater tidal wetlands, 84% to 98% may become inundated by 2100, and the ones that are not directly inundated will experience the impact of salt water intrusion and rising water tables. Due to the economic and ecological benefits of freshwater tidal wetlands, the State of Delaware lists their inundation and loss as one of the top five concerns relating to sea level rise, and The Nature Conservancy deemed them globally endangered. This project uses a dendrochronological approach to assess the impact of salinization on a forested, freshwater, tidal wetland to gain insight about how these valuable systems may respond to sea-level rise.

Tidal Atlantic white cedar swamps (Chamaecyparis thyoides), a freshwater wetland community, are now vanishing due to sea level rise and anthropogenic changes to waterways. The St. Jones River in Dover, DE was straightened through dredging in the early 1930’s, resulting in a dramatic salinity increase which stressed the thriving Atlantic white cedar population surrounding the river, leading to a dramatic die off. Many of these dead specimens stand today, providing us with the opportunity to examine the impact of increased salinity on this important fresh water wetland species.

We collected cross sections from eleven Atlantic white cedar snags from marsh adjacent to the St. Jones River and cores from 15 living specimens located along upstream tributaries, processing all samples with standard dendrochronological techniques. The resulting detrended tree ring chronology was then assessed for patterns related to increased salinity. Immediately after the dredging, the rings significantly narrowed and all specimens growing adjacent to the river died within 15 years. These results are important because they provide insight about how coastal forests may react to future sea-level rise.