PPS Arctic: Present day processes, Past changes, and Spatiotemporal variability of biotic, abiotic and socio-environmental conditions and resource components along and across the Arctic delimitation zone. PPS Arctic investigates the causes and consequences of changes in the circumarctic treeline zone, using fieldwork and remote sensing to study and model temporal and spatial aspects of ecological, social and cultural factors. Changes in the zone affect Arctic ecosystem processes, resource availability and the entire Arctic climate through changes in tree and shrub cover and in albedo, with global consequences.