Brand i Fulufjällets nationalpark : en brandhistorisk analys med förslag för framtida skötsel

Abstract: Fire has historically been of great ecological importance in the boreal forests of Sweden. The forest fire regime has, however, varied between different parts of the country. The objective of this thesis is therefore to investigate the fire history in Fulufjället National Park and, on this basis, give suggestions for future fire management. The reconstruction of fire history was done by cross-dating fire scars in samples taken from living and dead Scots pine (Pinus sylvestris). Local fire chronologies were established at 17 points in the forests in and around Fulufjället National Park by cross-dating fire scars on 54 samples. The oldest year-ring dated from year 968. A total of 28 fires were dated, with the earliest fire in the material occuring in 1142. The average fire interval, which is the time between two fires at one spot, was 136 years for the whole time period from 1336 to 1858. Before the 14th century, the samples are too few to support any conclusions about the length of the average fire interval. After the mid-19th century when timber became valuable, fires were almost completely excluded from these forests, due to efficient fire suppression efforts. Fires before 1336 and after 1858 have therefore been omitted in the calculations of average fire intervals. For the early period from 1336 to 1700, the average fire interval was 210 years. For the period from 1700 to 1858, when the number of inhabitants in this region more than doubled, the average fire interval was shorter; 89 years. This most likely reflects the increased number of fires that intentionally or unintentionally were caused by man. Since the chronologies in this study have a very good time depth, an average fire interval between 136 and 210 years should be useful as a template for future fire management in the National Park. Fire intervals in the National Park exceed the circa 75 years that earlier studies have found in neighbouring areas. This is probably due to the differences in elevation and topography between Fulufjället and the other study areas. On Fulufjället the alpine areas above the treeline have also burned, something that is otherwise very uncommon in the Swedish alpine region. Lightning ignitions have occurred several times during the last century. The largest fire, according to my sources, occurred in 1959 when 1200 hectares of land burned above the treeline on Fulufjället. Fires in areas above the tree line have, however, not been dated or included in the calculation of average fire intervals. In Fulufjället National Park the possibilities for letting lightning-ignited fires burn under supervision are very good, compared to other protected areas in Sweden. This is especially true for the areas above the tree line, where postponing suppression of the fires should be possible. In the forested parts, however, the decision will, for security reasons, most often be to extinguish fires. The suppression should, if possible, make use of natural fire borders that can be strengthened by watering or burning-out of the fuels ahead of the approaching fire. To maintain the historic average fire interval of between 136 and 210 years, an average of 34 to 53 hectares of coniferous forest must burn every year in the National Park. Since the majority of the spontaneous forest fires in the area probably will be extinguished, intentional burnings of standing forests are necessary. In this report, suggestions are given on areas where work with prescribed fire in the national park can be initiated.