Geographical variability of relationships between forest communities and soil nutrients along a temperature-fertility gradient in Norway

Abstract

Long term data sets of the National Forest Inventory (NFI) and the Monitoring Forest Health Program (MFHP) are analysed to find trends in relationships between boreal conifer forest communities ranked along a fertility gradient and soil nutrients of the humus layer (LFH-horizon) on podzol soils along a large temperature gradient. The temperature gradient covers the nemoral–boreonemoral, southern-central boreal and the northern boreal regions in the continental zone in Norway. For each region, the forest communities are ranked along a soil fertility gradient: communities dominated by heather species, mosses and lichens represent poorer sites than the communities dominated by grasses and herbs. Communities of grasses and herbs had a lower C/N ratio than communities dominated by heather species. In the colder regions, pH and base saturation were higher in the communities dominated by grasses and herbs than in communities dominated by heather species, while exchangeable acidity (Al+H) showed the opposite trend. Total N (N tot) was higher in the communities with grasses and herbs than in the heather dominated communities in the warmest region. Phosphorus, S, pH and base saturation were higher and exchangeable acidity lower in the colder regions than in the warmer ones. There were no or low significant differences in base cations among forest communities. The analyses show that concentrations of soil nutrients in the humus layer of podzol soils for a given community on a national scale are related to the temperature gradient. Partly these relationships are influenced by the dominant tree species. Furthermore the analyses show that concentrations of soil nutrients within a region are related to the fertility gradient, thus, to type of forest community. These relationships are not similar for the different regions. It is suggested that the differences in relationships between the concentrations of soil nutrients and the fertility gradient for the different regions are influenced by temperature, length of growing season, plant available soil nutrients and acid deposition. For the planning of sustainable forest management, this study shows that more research is needed on forest ecosystem processes to further and better explain the geographical variability in relationships between soil type, soil nutrients and humus layer, forest communities and tree species at national and regional scales.