Mapping and Monitoring of Mangrove Forests in the United States Using Landsat Satellite Imagery 1984-2009

Mangroves are salt tolerant species that primarily grow along the intertidal coasts of tropical and sub-tropical regions. mangrove forests in the US primarily occur along the coastal-intertidal zones of Florida, Louisiana, and Texas along the US Gulf and Florida Atlantic coasts. The largest tract of mangrove occurs in the Everglades in south Florida. Mangroves are less abundant and grow to relatively small stature along the US Gulf and northern Florida coasts. This study examined the areal extent and spatial distribution of mangrove forests in the conterminous US using Landsat satellite imagery acquired in 1984 and 2009. Unsupervised classification method followed by iterative labeling was performed to assess the areal extent of mangroves. Results showed that the US had a total of 227,660 hectares of mangrove cover in 1984 and a total of 245,632 hectares in 2009. Accuracy of the classified 2009 TM dataset was examined using high resolution imagery on Google Earth. An overall mapping accuracy of 94.83 percent was achieved, indicating that over 94 percent pixels in the classified 2009 TM dataset were correctly classified. Change analysis was conducted using post classification approach. Change analysis showed a significant gain of 19 percent (46,432 ha) and loss of 11.6 percent (28,467 ha) in the extent of mangrove forests in the study area over the 25 years. An intact cover accounted for 199,197 hectares. The majority of intact cover was located in southern Florida. Changes (gain/loss) in mangrove cover were identified to some extent across the study area. In the findings, a recent northward expansion of mangrove species was identified along the coasts of Louisiana, northern Texas, and northern Florida Atlantic coast. A decade of stable warm winter temperatures encouraged the northward expansion of mangrove species in those areas. Mangrove species are highly susceptible to winter freezes; these species were severely damaged due to recurring winter freezes in the 1980s in that regions. Winter freeze, hurricanes, and hydrological modifications were the major dynamics of mangroves ecosystems. Further, salinity stress, oceanic cyclones, erosions, and soil nutrients were other stressors. These dynamics have brought significant change to mangrove ecosystems throughout the study area; however, they vary significantly, spatially and temporarily. Results showed that employed remote sensing data and classification method were successful to discriminate mangrove habitats from non-mangrove forests and to perform change analysis in the study area. Research is, further, needed to identify accurate and reliable information and dynamics of mangrove ecosystems to better understand for the decisions and management of mangrove forests in the United States