Estudo dos manguezais degradados da costa oeste da Flórida durante os últimos 20 anos baseado em imagens de satélite e dados Lidar.

Abstract

The Gulf of Mexico presents one of the longest mangrove belts in southern Florida. This continuous mangrove strip has an approximate area of 2200 km2. Natural stressors such as hurricanes, storms, and other anthropogenic factors such as oil spills or pollution can trigger the dieback of the mangrove on the southwest coast of Florida. The dieback of the mangrove refers to the phenomenon where the mangrove forests experience a loss in the canopy that can lead to the decline or death of the trees. The effects of the dieback occasionally leave a scar of degradation in the mangrove forest. In the last century, with urban development in southwest Florida, the adverse effects of dieback seem to be gaining permanence. The present study identified the possible causes of the permanence of mangrove degradation associated with dieback over the last two decades. To identify these causes, the following methodology was used: a) classification of vegetation cover along the west coast of Florida, b) identification of dieback points in high-resolution satellite images, c) spatiotemporal analysis of dieback areas, and d) digital models of surface elevation and vegetation height. 86 dieback points (PD) were found grouped into 6 regions: Crawl Key, Key West, Marco Island, Pine Island, Charlotte, and Terra Ceia. 75% of the PD appeared between 2004 and 2007, coinciding with hurricane activity. In 2020, the total dieback area in southwest Florida was 119,69 ha. For the periods of 2014-2016 and 2009-2011, the areas of dieback recorded values of 116,47 and 127,89 ha, respectively, evidencing a dynamic of regeneration and degradation. The digital terrain models for Pine Island and Marco Island showed changes in the height of the tidal flat with variations between -2 to 45 cm. These variations may be linked to sedimentation processes, dissolution of carbonates in the tidal flat, or peat collapse associated with the mangrove soil. The mangrove trees reduced their height after the passage of hurricanes, particularly in the PD. Even though the PD showed regeneration, this process was slow, leaving a scar exposed to the tidal flat. This study revealed a direct relationship between hurricanes and the appearance of dieback.