Pasado, presente y futuro de los bosques de montaña (I)Expansión del bosque

Abstract

During the last decades, European mountain forests have suffered the consequences of the abandonmentof traditional agro-silvo-pastoral activities under the form of important forest expansion and densificationprocesses. In this work, we evaluated the importance of both processes and the consequences for the configuration of the landscape in the 3 National Parks established in mountainous areas of northern Spain:«Picos de Europa», «Ordesa y Monte Perdido» y «Aigüestortes i Estany de Sant Maurici». For that, we firstsemi-automatically reclassified aerial photographs from 1956 and 2016 into a binary raster with ‘forest’ and‘non-forest’ values. We calculated changes in forest cover as the ratio between the number of ‘forest’ pixelsand the total number of pixels in 0,25 ha cells. We finally calculated forest encroachment and densificationprocesses based on the change in forest cover observed in the cells during the studied period (1956-2016). Theresults of our work showed the occurrence of important forest encroachment and densification in the threeParks, but those processes were less important in «Aigüestortes i Estany de Sant Maurici». The NationalParks of «Ordesa y Monte Perdido» and «Picos de Europa» showed comparable levels of forest encroachment and densification in the areas historically protected in 1918 (when the Parks were created) and in theareas that were protected later (in the 1980s and 1990s, respectively). In contrast, «Aiguestortes i Estany deSant Maurici» showed substantially higher forest expansion and densification processes in the lands thatwere protected more recently (in 1996) compared to the ones initially protected in the 1950s when the Parkwas created. The processes of forest expansion and densification have derived in a homogenization of thelandscape, with a lower presence of open and transition areas (edges). Additional research and long-termmonitoring efforts are needed to advance in the understanding of consequences of these changes for thebiodiversity and functioning of these systems.