Assessing the fragility of forest remnants by using landscape metrics. Comparison between river basins in Brazil and Portugal

Abstract

The environmental vulnerability of a landscape is directly associated with any physical, geomorphological, and spatial factors which directly interfere with the ecological functionality of natural areas. Therefore, the composition, diversity, and structure of fragmented forest areas are essential to identify the patterns in the landscape and propose the most appropriate management measures for its conservation. The present study set out to analyse the applicability of landscape metrics for assessing the environmental fragility of forest remnants of different geographical conditions and phyto-physiognomies. This would contribute to landscape assessment and the diagnosis of remnants, and support decision making for strategic and effective environmental planning. The study areas selected were two river basins, the Atibaia river basin in Brazil, and the Cértima river basin in Portugal. The maps used as a basis for the selection of the forest remnants analysed were made available by public managers and date from 2015 for both basins. The analyses were performed with GIS software, and two groups of landscape metrics were considered: the first applied to the general landscape of the basin and the second applied to each remaining forest patch as a landscape unit. At the remaining forest level, the metrics analysed were the area, central area index, circularity index, shape index, distance from the nearest neighbour, proximity of the remnant to the road network, and proximity to the watercourse. The results showed that there are many remnants in both basins with predominantly small size and located close to each other. However, their fragilities vary in each basin, indicating that the applied metrics are effective tool for the preliminary diagnosis of natural vegetation remnants in areas with different geospatial and phyto-physiognomic conditions. Therefore, the results obtained are of great importance as a basis for formulating landscape development policies, by integrating appropriate land management strategies.