1. In Mediterranean mountainous areas, forests have expanded in recent decades because traditional management practices have been abandoned or reduced. However, understanding the ecological mechanism behind landscape change is a complex undertaking as the effects of land use may be influenced (reinforced or constrained) by other factors such as climate. 2. We used orthorectified aerial photographs to monitor changes in forest distribution in a set of 20 head-water basins (located in the Cantabrian Mountains of northwest Spain, at the Eurosiberian-Mediterranean limit) during the second half of the 20th century (1956, 1974, 1983, 1990 and 2004). In particular, we evaluated the combined effects of both land use history (comparing natural vs. anthropic basins) and microclimate (comparing shaded vs. sunny aspects) for assessing gain/loss rates and spatial distribution shifts of forests. Finally, in the stated scenarios of land use history and microclimate, we applied Species Distribution Modeling techniques (MaxEnt and BIOMOD) for defining forest expansion both spatially and statistically on the basis of topography, soil properties and mesoclimatic variables. 3. On average, forest cover increased from 10.72% in 1956 to 27.67% in 2004. The rate of expansion was significantly higher in natural basins and, particularly, on shaded slopes in recent decades. In all cases, the mean elevation of new forest patches increased during the study period, this trend being more evident on natural sunny slopes. The performance of the models and the magnitude of the effects varied across land use history, microclimatic conditions and biogeographic origin of forests. The main drivers of forest expansion were temperature and precipitation in late spring and early summer and soil properties, although land use history and plant diversity primarily controlled forest expansion rates and upward altitudinal shifts. 4. Synthesis. The combination of monitoring and modeling used in this work contributes to the understanding of forest dynamics in cultural systems, indicating that ecological succession is not a homogeneous process, but varies spatially due to human and abiotic constraints since historical times.
|Date made available||3 Apr 2015|
|Temporal coverage||1956 - 2004|
|Geographical coverage||Cantabrian Mountains of northwest Spain|