Highly Urbanized Mangrove Areas are Small in Size, Fragmented, and Missed by Large-scale Mapping Efforts

Mangroves are one coastal ecosystem that has experienced a long history of fragmentation and loss by urbanization. Yet, these small mangroves in urban areas are often missing from current wetland inventory due to lower resolution mapping methods and size classifications that may overlook these mangroves in highly urbanized areas. We mapped mangroves along a gradient of urbanization in Miami-Dade County, Florida (MDC) by combining several landcover databases, high-resolution imagery, and ground-truthing. We compared our newly mapped mangrove dataset with the Florida Fish and Wildlife Conservation Commission’s (FWC) current mangrove habitat dataset. We quantified differences in mangrove area, fragmentation metrics, and shape complexity across three urban intensities within MDC and between the datasets. We identified an additional 386 mangrove patches that were missed by the FWC map. The majority of these newly found mangroves were in the most urban regions of MDC. We identified average mangrove stand size in the least urbanized region is about 29 times bigger than those found in the most urbanized region. We also found that the FWC dataset significantly overestimated average mangrove stand size (18.32-ha) compared to the newly mapped mangrove dataset (1.43-ha) in the most urbanized region. Our results demonstrate that large scale wetland mapping efforts, like those of state agencies, provide valuable mangrove area estimations but may miss key fragmentation patterns by not including smaller mangrove stands scattered throughout highly urbanized regions. Habitat maps that capture these smaller, fragmented mangroves are needed to evaluate how urbanization shapes mangrove extent and ecosystem function.