Successional trends 219 years after fire in an old Pinus sylvestris stand in northern Sweden

We present results from repeated analyses (1962, 1993) of a permanent plot established in 1947, combined with retrospective stand age structure data, in an old Pinus sylvestris stand in Muddus National Park, northern Sweden. The study points towards a successional pathway governed by concurrent disturbance effects of climate variability, reindeer grazing and fire. This is intermediate to the two often advocated ideas on dynamics in boreal forests, that is, one of disturbance‐related tree regeneration/mortality and one of continuous regeneration. When the plot was established in 1947 the tree layer (> 1.3 m) consisted of 300 individuals/ha of P. sylvestris and 62/ha of Betula pubescens. Subsequently the stand has become more dense and the species dominance has shifted. In 1993, 362 P. sylvestris and 62 Picea abies individuals were present per ha, while no Betula individuals were found. The number of dead trees increased from zero in 1947 to 200/ha (Pinus) in 1993. Pinus was also the most common species in the sapling layer (< 1.3 m) throughout the study period, though the number dropped from 8912/ha in 1947 to 51% in 1993. Dead saplings decreased from 2650/ha in 1947 to ca. 50% in 1962, and only 9% in 1993. Temporal variations in mortality and sapling mean height coincided with variations in snow depth, indicating a critical period in sapling development when saplings are exposed at the snow/atmosphere interface. The number of living Picea saplings increased slowly until 1993; no dead saplings were found. Most Pinus recruited shortly after the 1774‐fire, and during the second half of the 1900s. The major part of the spruce regeneration took place during the later half of the 1900s. No successful Betula recruitment has occurred after the 1930s, and no live Betula were present in 1993, which might be explained as an effect of increased reindeer browsing – the reindeer stock has grown by 50% since 1961. Although subjected to high mortality, Pinus regenerated and maintained a seedling/sapling bank. In this way Pinus remained dominant in the tree layer after more than 200 post‐fire years. The importance of the shade‐tolerant Picea has slowly increased, while Betula has died off. Thus, even after 219 yr since fire there is an early successional trend in the stand. This suggests that an increased chronic disturbance (grazing/browsing by reindeer) has partly succeeded earlier discrete fire‐disturbance events, and maintained a continuous seedbed favouring the shade‐intolerant pine recruitment.