Vegetation changes and forest-line positions in the Swedish Scandes during late Holocene

The aim of this thesis was to elucidate the effect of human impact in contrast to climate on the vegetation in the northern part of the Scandinavian mountain range. The vegetation histories at four treeless Stállo settlement sites were contrasted to the vegetation histories in three forested reference areas at the same altitude as the settlement sites but lacking archaeological evidence of settlements. The Stállo settlement sites were probably established by Sámi people using the mountain areas for hunting and/or reindeer herding. They are generally dated in the range c. AD 650 to 1500, although it has been suggested that the main occupation period was confined to c. AD 800 to 1050. Peat stratigraphies from mires at the sites were recovered and analyzed for pollen, charred particles and macrofossils and pollen accumulation rates (PAR) were calculated. A statistical analysis was performed to separate the pollen from tree Betula and the shrub B. nana. In a simulation study the pre-settlement forest cover at one settlement site was explored. The results indicate that Betula trees were present at the Stállo settlement sites when the settlements were established. The settlement establishment was followed by a reduction in Betula tree cover at the sites. No such reduction was apparent in the reference areas suggesting that the decrease in tree cover was not due to climatic change. The deforestation during the Stállo settlement period was followed by a period of colder climate during the Little Ice Age, which together with continuing effects of human presence prevented reforestation of these areas. This long term absence of trees may have changed the ecosystem properties, hampering reestablishment of trees in these areas. This thesis demonstrates that historical human impact in the northern part of the Scandinavian mountain range can have a substantial effect on the local vegetation, which is still visible in the landscape today, several centuries after the settlements were abandoned. This long-term legacy in the landscape suggests that these areas are not “pristine” ecosystems, and has profound implications for our understanding of the responses of the tree- and forest-limits in these areas to e.g. climate change