The vegetation history has been examined by pollen, microscopic and macroscopic charcoal analyses in the vicinity of two alpine Stállo settlement sites and one forested 'Reference area' with no settlement remains in northwestern Sweden in the northern part of the Scandinavian mountain range. The acquired data provide indications of the effects of human activities on local vegetation during the settlement phase, and on ecological processes in both long-and short-term perspectives. The results show that one settlement site, Gieddeålge, was established just above the forest line in the Betula treeline zone, and the other, Varenodjukke, in the Betula forest. At Gieddeålge an increase in herbs and graminoids appears to have occurred c. 700 cal. BP (during the thirteenth century) suggesting that the vegetation was altered by nutrient addition, most likely related to human activities associated with the settlement. At Varenodjukke, the Betula trees around the settlement were cut down and the site developed into an alpine heath dominated by Betula nana, which still characterizes the site today. In the Reference area evidence of changes to the vegetation probably caused by human impact was also found from c. 3500 to 700 cal. BP. In conclusion, the vegetation currently present at Gieddeålge and Varenodjukke has been strongly influenced by previous human activities, which have clearly had profound effects, both short and long term, on the composition of the vegetation and the properties of the ecosystems in these areas. Further, when studying processes, such as anticipated global warming that will influence future patterns of vegetation in these forest-line areas, legacies of land use must be taken into consideration.

No abstract

The initial establishment of Picea abies in Sweden and Norway on a landscape level, between 3000 and 1000 years ago, was often preceded by recurrent fire and thereafter the influence of fire decreased. However, in some swamp forests, the absence of fire over the last 3500 years has promoted the continuous presence of deciduous trees, i.e. Picea has not established although it has been present regionally for over 3000 years. Our objective was to study longterm vegetation development and fire history in a Picea swamp forest located close (c. 600 m) to a deciduous swamp forest with a documented fire-free history in northernmost Sweden. The study included analyses of charred particles, pollen and ignition residues. Principal component analysis was applied to identify major changes in the pollen spectra. Our results showed that the current Picea swamp forest has developed from a deciduous fen and that fires affected the fen between 6700 and 2300 cal. yr BP. Picea abies established on the fen around 2200 cal. yr BP, following the last local on-site fire. The main factors responsible for the local vegetation development have been: fire (6700 to 2300 cal. yr BP); autogenous processes and climate (2300 to 1000 cal. yr BP); autogenous processes or anthropogenic impact (1000 to 300 cal. yr BP); anthropogenic impact through selective cutting and grazing (300 to 100 cal. yr BP); and autogenous processes and grazing (100 cal. yr BP to present). We conclude that fire facilitated the initial Picea abies establishment. Once established, Picea abies created local conditions that in combination with a colder and wetter climate prevented fire and the establishment of other tree species.