Long-term regeneration dynamics and successional trends in a northern Swedish coniferous forest stand

The natural age and stand structure of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) Karst.), and birch (Betula pubescens Ehrh.) was studied in a virgin forest stand in northern Sweden. The stand has been unaffected by fire during the past 500 years. It is suggested that the variations in age structure and invasion pattern are the result of low-frequency climatic fluctuations influencing seed production, germination, and early survival of seedlings. The periods of climatic amelioration that occurred during the 1870s and during this century have been especially favourable to pine, resulting in a pine-dominated regeneration underneath a tree layer where spruce and birch are the most abundant species. This is contrary to generally accepted theories concerning postfire successional trends in this part of the boreal zone. It is concluded that small gap-phase replacement of trees by climatically induced regeneration and mortality events probably is the reason for the general weak correlation between age and size of trees. It is also concluded that this postfire succession will not lead to a total spruce dominance during a continuous succession under prevailing climate regimes.