A new empirical index for assessing the vulnerability of peri-urban mangroves

Environmental vulnerability can be understood as a function of exposure to impacts and the sensitivity and adaptive capacity of ecological systems towards environmental tensors. The present study empirically evaluated the vulnerability of forest stands that make up the subtropical Perequê River mangrove (Paranaguá Bay, S Brazil) as the basis for a more appropriate management of its resources. This mangrove is located in the coastal municipality of Pontal do Paraná (Paraná, Brazil) and is part of the Perequê River Mangrove Natural Park, which is still not under a management plan. This study aimed to contribute to the future management plan of this conservation unit through an environmental diagnosis and an empirical evaluation of its vulnerability. The primary data, collected from 51 plots of 100 m(2) each, involved the evaluation of: 1) the exposure to solid waste, deforestation, trails, landfills, and constructions; 2) the degree of sensitivity according to the environmental conditions of each plot; and 3) the adaptive capacity according to the recovery and reproductive potential and structural complexity of the forests. These data were integrated to compose the empirical index of environmental vulnerability (VI) expressed as VI = (SI + EI) - ACI where SI is the sensitivity sub-index, EI is the exposure sub-index, and ACI is the adaptive capacity sub-index. Empirical indices calculated for local forests varied significantly due to differences in values of SI, EI and ACI. This variability defines the local mangrove as a mosaic of vulnerability conditions and suggests that the planning and implementation of local management actions consider such environmental heterogeneity. Applying or extending these actions should be based on local forest conditions at short spatial scales and should not be applied to the mangrove as a whole.