Quantifying the Role of the Net Evaporation Rates and Salt Concentrations on Mangrove Canopy Height across Mangrove Islands in Florida and Puerto Rico

Abstract:

Mangroves are a halophytic tree species residing in tropical and subtropical coastal intertidal zones. Although they provide several ecosystem services, such as coastal protection, nursery development and blue carbon storage, they are currently under threat due to anthropogenic influence as well as climate change. Early modeling studies have described mangrove vegetated area as a function of net evaporation rate (i.e., evaporation – precipitation), outer edge island salinity, and hydraulic conductivity of the soil. We coupled a process-based model with field observations from a number of isolated mangrove islands across the Caribbean to test the hypothesis that higher net evaporation rates generally lead to significantly lower mangrove canopy height. To answer this question, we extracted remotely-sensed mangrove canopy height distribution of islands across Florida Bay, Southern Puerto Rico and Western Florida generated by the NASA Goddard’s LiDAR, Hyperspectral & Thermal Imager (G-LiHT). After analyzing the histograms of canopy heights for each mangrove island, we find that the maximum canopy height is highest for Western Florida islands, where the outer edge salinity concentration is the lowest among the three locations. We also find that mangrove islands located in Florida Bay, where the net evaporation rate and salt concentration at the islands outer edge are highest, present the smallest maximum canopy height. Overall, these results show that a higher interstitial soil salinity, driven by higher net evaporation rates and higher salt concentrations in the water surrounding these islands, can lead to a significant reduction in mangrove vegetated area. Furthermore, these findings suggest that an increase in net evaporation rates across the Caribbean, as projected by Global Climate models, can lead to a significant reduction in mangrove island vegetation.