Constrained tree growth and gas-exchange of seawater exposed forests in the Pacific Northwest, USA

1. Rising sea levels under climate change may have significant impacts on coastal vegetation dynamics, yet the response of coastal forest growth, gas-exchange, and survival to seawater intrusion remains poorly documented. 2. We conducted a dendroecology study across six sites in western Washington, USA, to examine how tree growth, gas exchange (indexed by basal area increment, BAI, and wood δ13C, respectively), and survival varies with seawater exposure through two approaches. First, tree core samples were collected at a site where seawater exposure started only four years prior to sampling, which allowed a cause-and-effect test of the impacts of seawater exposure on trees, and second, samples were collected at five additional sites where we compared downstream to upstream trees under current sea-level conditions. 3. At the seawater intrusion site, BAI and carbon isotope discrimination (Δ) decreased significantly (p < 0.01) in the year of intrusion (2014) and stayed unchanged thereaf...