Impacts of forest biomass removal on soil nutrient status under climate change: a catchment-based modelling study for Finland

The environmental impact of different forest harvesting scenarios on soil nutrient status and water chemistry under current and future (IPCC A2) climate was evaluated for a random sample of lake catchments (n = 1066) covering Finland. Biomass removal scenarios were derived from a management-oriented large-scale forest model based on data from national forest inventories. Forest ecosystem sustainability was assessed by evaluating soil base cation balances as well as temporal changes (2010-2050) in soil base saturation and lake water acid neutralising capacity, using a dynamic hydro-geochemical model. The harvesting scenarios had very different effects on biomass and element removal as well as soil and water quality; only harvesting of above-ground woody biomass (stem-only or stem-and-branches harvesting scenarios) was predicted to be sustainable, i.e. not depleting the soil base cation pools in the long term. The most intensive scenario-whole-tree harvesting (including the removal of stumps and roots)-doubled the removal of biomass, tripled the removal of base cations from the catchment soils, and increased nitrogen removal fourfold. Climate change was predicted to have a positive impact by increasing the future supply of base cations from weathering, thus compensating their removal by biomass harvesting. However, additional inputs of nitrogen and potassium will be required to ensure sustained forest growth under intensive biomass harvesting.