Aim The aim of this work was to estimate on a regional scale the effects of nitrogen (N) deposition and harvest intensity on N-budgets in forest soils as a basis for strategies of emission reduction and sustainable forest management methods.
Location The calculations were applied to Sweden, a country with a managed forest area of 23 × 106 ha.
Methods Mass balance calculations, including N-deposition, N-fixation, N-loss through harvest, and N-leaching, were performed on a GIS platform using 5 × 5 km grids. Modelled deposition data together with spatial data obtained from the National Forest Inventory served as the basis for the calculations. Four different scenarios were run: a ‘base scenario’ involving present deposition and conventional forestry (stem harvest only); a ‘whole-tree harvesting scenario’ with present deposition and the harvesting of stems, branches and needles; a ‘decreased deposition scenario’; and a ‘whole-tree harvesting and decreased deposition scenario’.
Results There was a sharp N-accumulation gradient with an increase in accumulation in the direction of the south-western part of Sweden. In the ‘base scenario’, N-accumulation appeared in the country as a whole, apart from certain small areas in the northern part. Whole-tree harvesting led to net losses in extensive areas located mainly in northern and central Sweden. In most parts of the country, whole-tree harvesting combined with decreased deposition was found to result in net losses.
Main conclusions The intensity of the forestry has a strong impact on the N-budget. Conventional forestry in combination with the present deposition level results in a high net accumulation of N in the south-western parts of Sweden and accordingly, in a risk of unwanted environmental effects such as increased N-leaching. With whole-tree harvesting, the N-balance is negative in parts of Sweden, mainly in the northern and central parts. N-fertilization may become necessary there if the present level of forest production is to be maintained.