Modelling and mapping beech forest distribution and site productivity under different climate change scenarios in the Cantabrian Range (North-western Spain)

The beech forests in the Cantabrian Range occur at the southwestern limit of the distribution of the species and are very important for wildlife and biodiversity in the region. Climate change is expected to increase the frequency and severity of drought events over the next few decades in southwestern Europe, and establishing how this will alter the distribution, abundance and productivity of beech is fundamental for biodiversity conservation and management. In this study, we used spatially continuous environmental variables to develop spatial distribution and site-productivity models for beech forests in the Cantabrian Range and to project these models to different climate change scenarios. Two raster-based models of resolution 250 m were constructed to identify suitable habitat (species distribution model) and to estimate site index (productivity model) for beech in the Cantabrian Range. Of the 23 variables retained in the spatial distribution model, climate, soil and terrain were the most important (explaining respectively 51.2%, 34.2% and 10.1% of the variation). The productivity model retained only three variables (percentage of silt in soil, mean diurnal range of temperature and plan curvature of the terrain) but was able to explain 54% of the total variation. Future projections based on two emission scenarios suggest that suitable habitat will be drastically reduced by 2070 (loss of 40-90% of the area for the moderate and pessimistic scenarios, respectively). However, the projections do not imply current population removal rather it can be probably interpreted in less favorable conditions for seedling establishment, higher mortality rates and a reduction in local density of populations. Productivity projections for suitable habitat suggest a large increase in the average site index (from current 15.19 to 18.18 m) in the moderate scenario and an increase of only 34 cm in the pessimistic scenario. The study findings provide basic information for conservation biology and could be used by decision-makers to develop and implement actions for mitigating the impact of climate change on beech forests.