Bacia do Rio São Francisco em Minas Gerais: uma proposta metodológica para o mapeamento de ecorregiões.

Abstract

During the last century, the rapid demographic growth, the intensification of the agricultural and industrial activities, the deforestation, the indiscriminate use of pesticides and chemical defenses and the huge hydric demand by big agricultural and mining projects have progressively reduced the environmental quality in the São Francisco hydrographic basin. From the total area drained by the basin, approximately 37% are in the state of Minas Gerais, including the headspring of the main course and the majority of its big tributaries. Aiming to contribute to an efficient environmental management, this paper proposes one method and mapping of ecoregions in the parcel of the São Francisco basin that lies in Minas Gerais. In the main, ecoregions are understood as relatively homogenous areas by the geobiophysical point of view and in similar environmental conditions. They are projected to serve as spatial structure for the evaluation of researches, monitoring of ecosystems and environmental management. When considering the spatial differences in the capacities and potentialities of the ecosystems, the ecoregions stratify the environment by its probable response to disturbance. Among the existing types of classification, the present work adopted as initial reference the mapping of the ecoregions of the Central and South Americas developed by the CEC - Commission for Environmental Cooperation - an intergovernmental organization from North America. This mapping is subdivided in three levels, from Level I, in a wider scale, to Level III, with more detailing. At Level I of the ecoregions of the CEC, the study area is totally embraced by one single ecoregion (Eastern Highlands). Therefore, the mapping at Level I is not considered in this paper. Within the study area, the mapping is extended until Level IV, besides that, the ecoregions at levels II and III are redefined. The method that was developed used a qualiquantitative approach. Considering the assumption that in most of the cases the natural features represent the best sorters among the ecoregions, once they are physically palpable and visually perceptible, the limits at Level IV are given from the interpretation of boundering lines, coming from cartographic bases of relief, vegetation, soil use, climate and hydrography. To delimit the ecoregions at Level III, the method groups the ecoregions of Level IV through mathematical criteria that establish a relation among the percentage of each fitophysiognomy in the remainders of natural vegetation and the climate classification. At Level II the ecoregions of Level III are grouped by the predominance of the typical fitophysiognomy of the biomes in which they belong. In all, 65 ecoregions at Level IV were mapped as well as 8 ecoregions at Level III and 3 ecoregions at Level II. It is hoped that a consistent and usable proposal of ecoregions for the São Francisco basin in the state of Minas Gerais has been presented; that the simplicity of the method contributes to its easy application, adaptation and popularization and that the ecoregions that were mapped by the proposed method can serve as spatial reference to inventories and monitoring of the biota, thus contributing to the formulation of public policies and actions of environmental management and conservation.