Once abundant in the lower Florida Keys, forests of the foundational species slash pine (Pinus elliottii var densa) are rooted in limestone bedrock above a shallow freshwater lens on several remaining islands. Sea level rise has reduced the volume of these lenses and brought the groundwater closer to the surface, making them more vulnerable to storm surge flooding from hurricanes. In addition, beyond some minimum density, pines become too sparsely distributed to carry fire, and the ecosystem transitions to broadleaved mesophytic forest or to a salt-tolerant mangrove association. In September 2017, Hurricane Irma’s Category 3 winds and extensive saltwater flooding affected Big Pine Key, where the largest tracts of Keys pine forest persist. During the following winter and spring, we examined the response of pine trees and the understory flora in eight permanent 1-ha plots initially established in 1997-2000, as well as changes in groundwater salinity along transects established in 2012.
Results/Conclusions
Wind damage to pine trees was variable across the island, though many of the largest individuals were killed. However, at low elevations where data from wells and geophysical measurements indicated the persistence of salt water in the lens, browning of pine needles portended even greater levels of mortality. While the architecture of pine trees allow some to survive the impacts of strong winds, coastal pine forests susceptible to salt water flooding face a most uncertain future, and managers have few options to preserve them.