Historical land use and resource depletion in spruce-Cladina forests of subarctic Sweden

Abstract

Abstract Historical and repeated use of fire is thought to be responsible for poor forest regeneration on Norway spruce (Picea abies L.)-lichen (Cladina spp.) forests of subarctic Sweden; however, the role of nutrient limitation in this process has not been studied. Studies were performed on three paired stands of open spruce-Cladina forests and un-disturbed, Norway spruce-Scots pine (Pinus sylvestris L.)-feathermoss forests to evaluate whether repeated use of fire in ancient times led to depletion of nutrient resources which altered forest regeneration. All pairs were analyzed for vegetative composition, soil nutrient capital and availability, and total soil organic matter. Peat cores collected in neighboring bogs were used for pollen analyses. Spruce-Cladina forests were found to have significantly reduced N capital and little N2 fixation capacity. Spruce-Cladina forests had lower concentrations of mineral soil P compared to reference forests. Pollen records suggest that these sites were historically mixed spruce, pine forests, but under the influence of recurrent fire exhibited a marked peak in charcoal occurrence at about 550 calibrated years BP and a decrease in tree pollen accumulation at circa 500 calibrated years BP. Carbon dating of charcoal in hearths located on the three sites place regular human occupation of this from circa 600–300 calibrated years BP. The open spruce-Cladina forests of subarctic Sweden are likely a product of recurrent use of fire by humans. By adopting a long-term perspective it is possible to understand land-use legacies even in remote ecosystems that are considered “natural” today.