Coastal Forest Dieback in the Northeast USA: Potential Mechanisms and Management Responses

A number of studies have documented coastal forest dieback as a historical and ongoing process across the Northeast US region. To further develop a current understanding of the state of knowledge, review adaptation and response measures available to land managers, and to identify research and management needs, we conducted a literature review, interviewed experts, and convened a workshop bringing together scientists and land managers. A synthesis of the above suggests that the most important proximate mechanisms driving coastal forest dieback in the Northeast US are sea level rise-induced changes in the groundwater table in concert with increased saltwater inundation related to storm surges. What sets our conceptual model apart from prior work is the greater emphasis placed on the role of rising fresh groundwater levels in increasingly stressing the forest vegetation and decreasing regeneration potential. Episodic storm surges often exceed the salinity or saturation tolerances of existing trees leading to a wave of mortality that leaves the site inhospitable to subsequent regeneration. Maintaining functioning coastal forests across the Northeast US will require that the marsh and forest ecosystems be considered as an integrated unit when determining an appropriate adaptation response. With a better understanding of each of the sea level rise-induced mechanisms at work in these ecosystems, managers may be better prepared for the changes ahead and facilitate proactive adaptation strategies. Easements or buyouts are vital to ensure that there is ample space for the marsh and upland systems to migrate landward together. Forward thinking land use planning is needed to promote the “no net loss” of both marsh and coastal forest ecosystems to ensure the continued provision of their vital services to society.