Regionalized nitrogen budgets in forest soils for different deposition and forestry scenarios in Sweden

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.