Evaluation of Tidal Fresh Forest Distributions and Tropical Storm Impacts Using Sentinel-2 MSI Imagery

Situated in the transitional zone between non-tidal forests upstream and tidal fresh marshes downstream, tidal fresh forests occupy a unique and increasingly precarious habitat. The threat of intensifying anthropogenic climate change, compounded by the effects of historical logging and drainage alterations, could reduce the extent of this valuable ecosystem. The overall goals of this project were to identify forest communities present in the Altamaha tidal fresh forest; develop satellite imagery-based classifications of tidal fresh forest and tidal marsh vegetation along the Altamaha River, Georgia; and to quantify changes in vegetation distribution in the aftermath of hurricanes Matthew and Irma. Based on vegetation data gathered during our field survey, we identified at least eight distinct forest communities with hierarchical clustering methods. Using Sentinel-2 Multispectral Imager (MSI) satellite imagery and a balanced random forest classifier, we mapped land cover for six anniversary images from 2016 to 2021 to examine changes in vegetation distributions. Overall classification accuracies ranged from 80 to 86%, and we were able to accurately discriminate between several classes at the species level. Over our six year study period we did not observe any substantial changes in land cover, including the forest-marsh transition, suggesting resilience to tropical weather impacts. We postulate that this stasis may be due to the large volume of freshwater delivered by the Altamaha River and the extensive tidal marshes of the Altamaha estuary, which protect freshwater wetlands from the short-term effects of saltwater intrusion by reducing salinity and buffering them from acute pulse events such as hurricane storm surges