Fragmentação, conservação e restauração da caatinga

Abstract

Reliable landscape information at large spatial scale is essential for decision makers dealing with biodiversity conservation, ecosystem restoration, resource management, and environmental policy. The Caatiga biome, a semiarid ecosystem that spreads over 826,000 km2 of the Brazilian territory, despite being highly fragmented, still holds half of its original vegetation cover. The remnants, however, have been disturbed for centuries by a multitude of different anthropogenic threats, including overgrazing, logging, fire, hunting, among others. Despite that, the area under protection is below international agreements and restoration endeavors have been scarce. Based on a multitude of spatially explicit analyses, the four chapters of this Thesis had as main objectives: (1) to analyse quantitatively the fragmentation structure of the Caatinga biome, (2) to estimate the level of potencial cronic anthropogenic disturbance of the Caatinga fragments, (3) to identify the priority areas for restoration in the Caatinga biome, based on landscape connectivity and number of endangered plant species, and (4) to compare habitat loss and deforestation rates of Conservation Priority Areas of the Caatinga, defined by the Ministery of Environment (MMA), with those in other Brazilian biomes. Geographic Information System analyses, performed on officially available information, show both good and bad news for the biome. Despite the fragmentation already experienced by the biome, the level of functional connectivity remains relatively high among fragments and half the remaining vegetation is preserved in large fragments (≥ 50,000 ha), indicating the existence of precious pro-active conservation opportunities. In contrast, the fragmentation level is intense and 90% of the remaining vegetation occurs at distances lower than 2.5 km from the forest edge, allowing an easy access to the already scarce Caatinga core area. An Index of Chronic Anthropogenic Disturbance (IPC), which synthesizes the potential perturbation effect of 14 primary variables, indicates that all Caatinga fragments are under some degree of perturbation. However, important regional heterogeneity was detected with more disturbed fragments occurring in the Northern, Eastern, and Central regional of the biome. Although the mean IPC of the fragments is not correlated to its area, IPC drops non-linearly with edge distance, showing relatively stable core areas after 5 km. Landscape simulations, testing the importance of each watershed for landscape connectivity, allowed the identification of relevant areas for restoration. By crossing this criterion with the number of endangered plant species in each watershed, we were able to identify a subset of key watersheds for restoration that hold only 8% of the deforested area of the biome. By estimating the deforestation rate of all Priority Areas for Conservation of the Brazilian terrestrial biomes, it was possible to demonstrate that the Caatinga and the Cerrado biomes exhibited the higher rates of habitat loss, further demonstrating the vulnerability of the biome. Hopefully, the information here provided can help national and state decision makers to advance biodiversity policies for biodiversity conservation, restoration, and management.