Dynamics of Long-lived Foundation Species: The History of Quercus in Southern Scandinavia

Abstract

(1) The long-term history of Quercus in southern Scandinavia has received little attention despite its important role in modern conservation. In this study the 4000-year dynamics of Quercus, its habitat and other important taxa were analysed with pollen data from 25 small hollows and 6 regional sites across southern Scandinavia. The aim was to provide a context for understanding the species’ current status and managing its future dynamics. (2) The results indicate that Quercus is much less abundant today than at any time during the previous 4000 years and corroborate the rapid decline reported in 18th- and 19th-century historical records. Modern pollen percentages are 45-60% of 17th-century values and only 20-35% of the maximum values reached in the 3rd century. (3) A strong positive correlation exists between the abundance of Quercus and the abundance of Tilia, Corylus and Alnus, which also experienced a steady decline across the region in the last two millennia. Climate change is the broad-scale driver of the observed dynamics, but human activity introduced considerable variation in the regional and temporal details of these changes. In the hemiboreal northern part of the study area the decline of Quercus appears to be controlled largely by competition with other tree species (especially Pinus and Picea), mediated by harvesting. In the temperate south part Quercus forests decreased through deforestation for agriculture. (4) Multivariate analyses indicate that although substantial phytogeographical variation has existed through past millennia the regional vegetation is more homogeneous today than in earlier periods. (5) Synthesis. The long-term decline and recent rapid reductions in Quercus populations throughout southern Scandinavia are striking and indisputable. From the perspective of both the populations of Quercus and its associated species of insects and epiphytes, the recent rate of decline is extremely rapid. Given the former abundance, longevity and capacity for persistence of Quercus, current populations of Quercus and its associated species appear to represent biological legacies in the midst of protracted decline. Based on these results, a reasonable conservation goal is to restore the abundance and distribution of Quercus to levels that preceded the drastic decline in the 18th and 19th centuries.