Avaliação dos impactos antropogênicos sobre a estrutura da paisagem do Parque Nacional dos Lençóis Maranhenses.

Abstract

Loss of habitat through the conversion of land use is considered a major cause of the reduction of terrestrial biodiversity on planet Earth. The Lençóis Maranhenses National Park (PNLM) was created in 1981 on the eastern coast of Maranhão State, Brazil, to protect the largest dune field in the Americas and associated mangrove and sandbanck vegetation ecosystems. Although Brazilian National Parks do not allow human occupation, the PNLM was created in an area occupied by traditional populations and to this day no land regularization action or establishment of Commitment Terms (TC) with families have been implemented to reduce threats to the conservation of the biodiversity. These families practice subsistence agriculture in the PNLM and surroundings, affecting ecosystems through the conversion of land use. This work aims to make an analysis of the conversion of land use and occupation in PNLM and surroundings for conservation and territorial planning purposes; to calculate the average annual deforestation rate in the last 15 years and to verify if there is a statistical difference between this rate inside and outside the PNLM; propose appropriate conservation strategies. A fine-scale mapping of high resolution satellite images was performed by supervised classification of the PNLM land cover and 3 km of its immediate surroundings. The mapped area was divided into hexagonal Analysis Units (AU) of 1000 ha each. The following class-level metrics were calculated: the core areas of the different land cover classes - dune fields (CA-DUNES), water bodies (CA-WATER), dense restinga (CADENSE), grassland (CA-SANDY), mangroves (CA-MANG), anthropogenic activity (CAANTRO), secondary vegetation (CA-SECOND) - and percentage of vegetation in the UA (NV-VOC). At the landscape level, the Shannon Diversity Index (SHDI) was calculated. Pearson correlations were performed among the metrics to verify those more correlated with anthropic activities. The average annual deforestation rate for the last 15 years was calculated at 30 sampling units of 100 ha each located outside and within the PNLM. An ANOVA was performed between the deforestation rate inside and outside the PNLM to verify if there is statistical difference between them. The analyzes carried out showed that the anthropic effects are present throughout the protected area, but they affect to a greater degree the formations of sclerophyte restinga (CA-DENSE), to the detriment of restinga formations in scattered moats (CA-SCATTER), restinga (CA-GRASS) and mangroves (CA-MANG). Cultures were mainly responsible for the loss of habitat, followed by trails and settlements. Conversion of land use resulted in increased environmental heterogeneity (SHDI) with loss of fragments of pristine habitats and increase in secondary vegetation, indicating impoverishment of vegetation. The mean annual deforestation rate calculated was 0.5% per year and no significant difference was found in areas located outside and within the PNLM, indicating that conservation status does not prevent the destruction of habitats. Conservation strategies were defined based on the UA vegetation cover: Conservation; Conservation with Management; Management; Management and Restoration, and; Restoration.