From broadleaves to spruce - the borealization of southern Sweden

Mixed or broadleaf forests were once common in many regions of Northern Europe, whereas today conifers often dominate. The aim of the study was to investigate the spatial and temporal patterns and processes which underlie this transition to Picea abies dominance in southern Sweden. We use recently developed paleoecological methods to determine long-term changes in the relative abundance of tree species, and digitalized National Forest Inventory (NFI) databases to assess more recent changes in the spatial coverage of Picea throughout the region. The novel combination of the two databases reveals that Picea became a widespread and abundant species in many parts of southern Sweden around 1000 years ago. After a brief decline in abundance starting around 500 years ago, NFI data indicate a rapid increase in the volume of Picea between 1920 and 1950, prior to the large-scale introduction of Picea-dominated plantation forests. The available evidence suggests that abandonment of forest grazing and slash-and-burn cultivation, as well as selection cutting benefited the natural establishment and growth of Picea during the first half of the twentieth century. Hence, prior to the impacts of industrialized forestry that began in the 1950s, other processes were already favouring increased Picea abundance.