Paisagens fragmentadas: métricas da paisagem e geossistemas como subsídio à proposição de conectividades florestais para a bacia hidrográfica do ribeirão Jacutinga, Zona da Mata Mineira

Abstract

The fragmentation of original vegetation is inherent to all Brazilian biomes and causes environmental problems that require control and proposals based on the expansion of forest connectivity. The ribeirão Jacutinga watershed, located in the municipality of Santa Rita de Jacutinga, in the Zona da Mata region of Minas Gerais, encompasses local vegetation of the Submontane Semideciduous Seasonal Forest and Montane Semideciduous Seasonal Forest types in lower-altitude terrain, Upper-montane Semideciduous Seasonal Forest and Uppermontane Dense Ombrophilous Forest at higher altitudes, with rocky grasslands characteristic of this type of lithology also occurring across quartzite formations. It exhibits forest fragmentation mainly in its middle-lower course, composed of floodplains and rounded hills and hillocks with gentle slopes under diversified land use, with no geomorphological constraints on land use and occupation, such as landform and slope. It brings together forest fragments of various sizes and shapes that are considerably distant from one another, especially in lower-altitude areas, exposing forest discontinuity and habitat fragmentation. The ribeirão Jacutinga watershed is composed predominantly of small properties encompassing diversified land use, including commercial eucalyptus spp forests, mosaics of seasonal crops, pastures for cattle raising and forest remnants of varying sizes throughout its entire extent. Due to these aspects, the present study proposes an approach related to forest connectivity based on landscape metrics grounded in the circularity, size, shape and distance between forest fragments. Based on landscape metrics, it aims to develop a proposal focused on reducing the impacts of fragmentation through a connection network linking internal and external portions of the ribeirão Jacutinga watershed. Corridors formed by expanding fragments present in the study area that do not function as habitat islands and by establishing new fragments preferably in permanent preservation areas, considering the restrictions on the use of these areas and their reduction under the new rules for identifying and delimiting permanent preservation areas. The study drew on contributions from Landscape Ecology and Geosystems Theory, both complementary approaches that helped achieve an integrated understanding of the study area, also seeking to understand forest connectivity beyond the boundaries of the ribeirão Jacutinga watershed due to the dispersal of biotic organisms into adjacent watersheds, especially in the northwestern and northern sectors under the direct influence of the Serra da Mantiqueira. In this sector, geomorphological constraints act as barriers to land use and occupation, promoting significant corridors of continuous forest remnants. The study area presents sectors of continuous vegetation in the upper watershed, representing the largest habitat island dispersing biotic organisms throughout the landscape, while the middle-lower watershed exhibits a fragmented landscape with smaller discontinuous fragments associated with seasonal crops, silviculture and pasture. In these sectors, the most degraded pastures occur, with ongoing erosional processes and extensive deforestation of permanent preservation areas. The external area of the watershed corresponding to the Vale do Café in the state of Rio de Janeiro exhibits considerable fragmentation, with the occurrence of few fragments.