Abstract. Despite increasing temperatures since the end of the Little Ice Age (ca. 1850), wildfire frequency has decreased as shown in many field studies from North America and Europe. We believe that global warming since 1850 may have triggered decreases in fire frequency in some regions and future warming may even lead to further decreases in fire frequency. Simulations of present and future fire regimes, using daily outputs from the General Circulation Model (GCM), were in good agreement with recent trends observed in fire history studies. Daily data, rather than monthly data, were used because the weather and, consequently, fire behavior can change dramatically over time periods much shorter than a month. The simulation and fire history results suggest that the impact of global warming on northern forests through forest fires may not be disastrous and that, contrary to the expectation of an overall increase in forest fires, there may be large regions of the Northern Hemisphere with a reduced fire frequency.

The occurrence of forest fires in the Muddus National Park (area, 50 000 ha), just north of the Arctic Circle in northern Sweden, was investigated on 75 separate sample plots. Between 1413 and the present, evidence of 47 fire years was obtained by dating the fire scars on living Scots pines (Pinus sylvestris), the oldest of which had germinated in 1274. The fire traces found on the sample plots were fire scars on living or dead trees or charcoal fragments in the humus layer. Plots lacking all traces of former forest fires were mainly those situated on sites surrounded by extensive mires. Forest fires were shown to have occurred in the five different types of forest investigated. The commonest frequencies of fires in the pine forests occurred with the interval 81–90 years, while the mean frequency was 110 years. The mean interval of time elapsed since the last forest fire occurred in the pine forests was 144 years. Some of the major fire years in the Muddus area coincide with forest fires in other parts of northern Sweden, in the taiga of western Russia, and in central Siberia.

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SUMMARY The performance of Pinus sylvestris L. and Picea abies (L.) Karst has been studied in relation to the fire regime from the 1200s up to present in an old‐growth boreal forest area, The J‐shaped age distribution of pine during the study period, suggests a stationary pattern in the landscape. The spruce age structure (from the 1600s onwards) also points towards a J‐shape, although with slight deviations. No significant changes in total pine or spruce regeneration occurred in response to the significantly prolonged fire cycle (from 187 to 371 yr) around 1870. This break in the fire cycle might possibly have a climatic background.

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Abstract. 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.

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