Long-term spatio-temporal dynamics and historical continuity of European aspen (Populus tremula L.) stands in the Koli National Park, eastern Finland

Abstract

Summary Although the European aspen ( Populus tremula L.) is regarded as a keystone species for the biodiversity of northern Europe, its mechanisms of regeneration and persistence under old-growth conditions without large-scale disturbances have remained obscure. The aim of this paper is to describe the long-term dynamics and regeneration of European aspen in the old-growth forests of the Koli National Park, eastern Finland, in order to gain a better understanding of the occurrence of this species under natural forest conditions. The park includes both natural forests and forests that were previously managed. The long-term occurrence of aspen populations was determined on the basis of inventory data available for the years 1910, 1936 and 2004. Aspen is shown to have occurred at least temporarily over 34 per cent of the total forest area (840 ha). In addition, 13 per cent of the forest area continuously supported stands that contained large aspen trees between 1910 and 2004. In areas where no management took place (6.4 per cent of the area), about one-third of all the aspen stands contained large trees and persisted throughout the period. The results show that aspen can maintain long-term occurrence in old-growth forests and that the species is not only transient or confi ned to young successional stages. Areas where aspen regeneration is possible, as deduced from its long-term occurrence should be regarded as highly valuable for biodiversity because they offer long-term habitats for several threatened species that are associated with aspen trees. Recent changes in ecological conditions, however, may affect this in the future. Most notably, the increased population of large mammalian browsers may make aspen regeneration more diffi cult and should be taken into account when restoration and management measures are planned.