Uso e ocupação do solo e a relação com a fragilidade dos remanescentes florestais na bacia hidrográfica do Rio Cértima/Portugal

In Portugal as in large areas of Mediterranean Europe there were important changes in land use and occupation, especially after the second half of the twentieth century. These changes include agricultural abandonment and afforestation of land previously occupied by agriculture as a result of the rural exodus and also of adopted public policies. Thus, the present work aims to evaluate the land use and occupation, the physical (climatic, geomorphological and pedological) and historical factors and the fragilities identified in the remnants of native vegetation existing in the Cértima River Basin in Portugal. Therefore, a general diagnosis of the study area was performed from the following geoindicators: biome; climate; geomorphology; geology; pedology; hypsometry and declivity. Then, landscape metrics from three categories, size, border and shape, were calculated; and are applied to the basin in general, considering the mapped forest remnants. To assess the quality of existing forest vegetation, a field analysis was carried out at selected locations in the Cértima river basin using the Landscape Assessment Protocol (LAP) method. Thus, it can be observed that most of vegetation cover in the Cértima river basin is composed of eucalyptus, and a total of 1220 forest remnants were identified, occupying an area of 8,547.05 ha, equivalent to 15.89% of the basin area.