Long-Term Dynamics of High-Altitude Populations of Pinus sylvestris in the Swedish Scandes

Abstract

The age structure of Scots pine (Pinus sylvestris L.) was studied, on a regional basis, in a narrow altitudinal zone well below the altitudinal tree-limit in the Swedish Scandes. The study period covered the last c. 400 years. Regeneration success was related to changes in summer mean temperature and thermal conditions during the late winter and spring. A positive impact of the twentieth-century climatic improvement was found. A marked regeneration gap occurred during the climax (AD 1680-1720) of the Little Ice Age. Possibly the coldness of this period increased mortality rates even of adult pines. The age structure suggests that within the altitudinal and temporal interval studied pine populations are in a dynamic steady-state condition. Regeneration takes place even during climatically unfavourable periods. This differs from both more and slightly less marginal sites where populations are more vulnerable due to climate and climate-fire interactions, respectively. The existence of this zone of relative population stability is an important feature when discussing Holocene biogeographical changes.