MANGROVE BIOPHYSICAL PROPERTIES AND COASTAL GEOMORPHOLOGY: A REMOTE SENSING STUDY

Mangrove forests are found throughout the tropics and occur as dense forests along calm tropical coastlines. They are an important coastal resource, providing a barrier to hurricane storm surge and tsunami inundation and serving as a nursery and primary habitat for many fish and bird species. Mangrove habitats are threatened worldwide by coastal development, aquaculture, and sea level rise, and it is estimated that about half of the world's mangroves have been lost. In the continental United States, mangroves are limited to the Florida Peninsula, notably in Everglades National Park and the Florida Keys. In this study, high spatial resolution multispectral imagery (IKONOS 4 m/pixel, blue, green, red, and near-IR bands) was used to produce maps of the mangrove-dominated 400 hectare Long Key State Park in the Florida Keys. The imagery was useful in discriminating between mangrove types (red and black mangrove), and between mangrove and non-mangrove (tropical hardwood hammock) vegetation, with supervised classification accuracy of over 90%. High-resolution airborne LiDAR data was also collected over the study area with 0.5 meter postings. Both first and last laser returns were recorded, providing digital elevation data of the top of the mangrove canopy and the ground (bald earth) surface. This DEM data provides canopy height which can be used to estimate mangrove biomass and other biophysical parameters. Field measurements of mangrove tree heights reveals that LiDAR-derived heights are systematically under-estimated, and we calculate a LiDAR-to-field height conversion for several DEM spatial resolutions. Multispectral vegetation characteristics, such as the Normalized Difference Vegetation Index, show only a moderate correlation with LiDAR-derived heights. The bald earth DEM product reveals important topographic and geomorphological relationships with red and black mangrove thickets, as well as the erosional effects of recent hurricanes on the mangrove habitat.