Age and Size Structure of Pinus Sylvestris Populations on Mires in Central and Northern Sweden

(1) The age and size structures of peatland populations of Pinus sylvestris were studied at eight different sites along a latitudinal gradient from central to northernmost Sweden (6 1-67N). (2) Three of the northern populations had age structures with two or several peaks representing periods of successful pine regeneration. The five remaining populations had unimodal age distributions. The youngest age class was the modal class in only three populations. (3) Stem diameter and height were significantly correlated with age, but the variation in size for any given age was large in all populations. (4) Size distributions were skewed towards larger size classes in all populations. (5) The age structures of most populations suggest a wave-like regeneration pattern. Only the age distributions of the two southernmost populations may reflect a more-or-less constant rate of pine recruitment. No signs of major disturbances could be found at the study sites, and it is suggested that the periodic increases of successful regeneration may be the result of interactions between different age and size classes of pine. (6) Periods of abundant regeneration showed a striking coincidence in the three studied populations which had several peaks in their age structures. These periods also coincide with periods of successful regeneration documented by studies in high-altitude pine populations on mineral soil in the same region of northern Sweden. This suggests that a common external factor, like the fluctuating climate, has played an important role in synchronizing these patterns.