Tree recruitment, growth, and distribution at the circumpolar forest–tundra transition: introduction

Causes and consequences of changes in the circumpolar forest–tundra transition have received recent interest due to the increasing awareness of human-caused global climate change. The International Polar Year core project PPS Arctic focused these topics through exploring processes, changes, and spatiotemporal variability of biotic and abiotic drivers of change in the forest–tundra transition. The papers in this special feature present constraints and drivers of tree recruitment and tree encroachment of tundra areas, climate – tree growth relations in the ecotone, and changes in tree spatial pattern across the forest–tundra ecotone.