Efectos ecológicos del cambio de uso del suelo en el espacio natural de la Sierra de Ancares (León)análisis de cambios mediante SIG y teledetección

Abstract

During last decades, several biophysical and socioeconomic factors have modified the landscape of the Natural Park of La Sierra de Ancares, located at the western extreme of te Cantabrian Mountains, determining its current structure and function. In this work, we analyzed landscape dynamic, at different spatial and temporal scales, also evaluating several future land cover change scenarios. These analyses need to be understood by explicitly considering the fragility of mountainous systems, where the interactions between humans and nature interplay since historical times in a mi stable state of equilibrium. At a regional scale, landscape dynamics was characterized by classifying a yearly database of Landsat images, from 1991 to 2004, which provided a continuous series land cover maps. Due to the high heterogeneity of the territory, we developed a spatially-explicit analysis of uncertainty based on fuzzy logic, allowing to distinguish between a hard area, containing relevant units (i.e. land covers), and an uncertain area, representing possible errors in the classification process. As a result, we obtained several land cover inventories which allowed to define the most important land cover changes of study area at the scale of the analyses with higher levels of reliability (or accuracy). All this information was accomplished in spatially explicit landscape change models based in Markov chain statistics, used for predicting future slates of the system under different climatic and environmental scenarios. These simulations me useful as a theoretical basis for developing suitable forestry practices applicable into territory management. Changes occurred in transitional areas between forests and shrublands showed random variations during study period due to the uncertainty, suggesting the necessity of a change scale in the analysis. Therefore, at a local scale, aerial photographs and ortophotos were obtained for the years 1956, 1974, 1983, 1990 and 2006 allowing to characterize land covers with higher level of detail in 20 head-water basins distributed across the Natural Park. With this information, we determined forest expansion rates and the potential occurrence of a “escalator effect” (upward movements in altitude) since 1950’s. In general terms, land cover changes showed two different components. On the one hand, forests fires and tree fellings, the depopulation of rural areas and land abandonment, together with the disappearance of agriculture and livestock farming, mining industry and urbanization processes have involved a recurrent dynamic in landscape structure and composition (forest fires, vegetation recoveries, the invasion of old fields by shrubs and forests, etc.). On the other hand, but concurrently, forests can steadily move upwards in attitude or towards the northernmost slopes looking for compensating less favorable particular thermo-pluviometric conditions (as higher rainfall deficits during drought periods). This effect has been found in the study area in the sunny slopes of natural basins (i.e. where exist mature forests in a good state of conservation, not affected by human disturbances during the last decades). The multidisciplinary and multiscale approach presented in this work allowed to obtain a comprehensive knowledge of the territory, which can be used to develop locally-tailored resource management strategies.