Global change in the European Alps: A century of post-abandonment natural reforestation at the landscape scale

Natural reforestation is one of the dominant processes in marginal mountain areas of the Northern hemisphere. There is a globally relevant need to predict where and when natural reforestation is likely to occur and what the ecological and social effects might be. We conducted a systematic review and meta-analysis of land use/land cover change (LULCC) case studies investigating spatial patterns of post-abandonment natural reforestation in the European Alps. We selected the Alps as representative of global change effects on forests due to their history of LULCC since the 19th century. Our aim was to identify the most important socio-ecological influences on reforestation and discuss implications for planners and managers. At the regional scale, we summarised the spatiotemporal distribution and methodological approaches of the case studies. At the municipality scale, we explored the relationships between reforestation rate and socio-economic variables using multivariate statistics. At the landscape scale, we assessed climate, topographic, and socio-economic drivers on reforestation using Random Forest regression. We observed a lack of studies in the northeastern region of the Alps. Population density, road density, and the proportion of workers employed in industrial vs. agricultural job sectors were the variables most highly correlated with reforestation. Reforestation rate was greatest in south-facing slopes of dry landscapes within remote and sparsely populated municipalities. We advocate for a dynamic harmonised LULCC geodatabase to capture the nonlinearity of past LULCC in training both correlative and process-based models for landscape planning.