A paisagem cárstica da bacia do Rio Sobrado, região sudeste do Tocantins, sob a ótica da geoecologia da paisagem

Abstract

The karst landscapes offer diverse natural resources and ecosystem services. Because they are highly fragile, these environments need integrated planning to avoid or mitigate the environmental impacts of their occupation. To understand the structure and dynamics of the karst landscape of the Sobrado River watershed, located in the southeast region of the state of Tocantins, Landscape Geoecology presents itself as a theoretical and methodological model since it analyzes the interaction between natural and social dynamics. To this end, methodological procedures were carried out involving the delimitation of the study area and a survey of the environmental information that characterizes the Sobrado River watershed (BHRS, in the original acronym); preparation of land use and land cover maps for the years 1985, 2000, 2015 and 2020; ecological analysis with an emphasis on the results obtained by landscape metrics; geographical analysis based on the compartmentalization of the geoecological units of the landscape, using the overlapping of themes: geomorphology, declivity, hypsometry, geology and soils, and subsequent association with the levels of current land use and occupation; preparation of the exploratory map of karstic phenomena; and multitemporal analysis of land use and land cover and fragmentation for the geoecological units with the presence of karst features and tourist attractions. Thirty-seven geoecological units were identified in the BHRS, with pasture being the predominant use classification in the watershed. It was found that the geoecological units located at the top of the Serra Geral are currently used for temporary agriculture. However, the units in the escarpment areas and near the Serra Geral have preserved native vegetation. In the units with gentle to intermediate relief, native vegetation areas have been converted into pastures or agriculture, followed by the occurrence of the process of fragmentation of the remnants and a decrease in their quality, mainly the replacement of fragments of the grassland formation and the subdivision of fragments with an area of more than 100 hectares into those belonging to the Savannah and Forest Formation. By overlaying the map of geoecological units with the exploratory map of karstic phenomena, it was found that 14 units have karst features and tourist attractions within their scope, with characteristics that portray the presence of the Bambuí Group and the Urucuia Group, respectively, soils that are more susceptible to the occurrence of erosive processes and the advance of human activities over native vegetation and the fragmentation of remnants. This situation has adverse effects, such as modifying the landscape and increasing human pressure on biodiversity and ecosystem services. On the other hand, remnants of the Savannah and Forest Formations still predominate, linked to massive outcrops of carbonate rocks, riparian forests, and areas with steep terrain. The information obtained can support the implementation of sustainable environmental planning and management to promote the rational use of natural resource.