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 managementoriented 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.

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In this work the aim was to determine how carbon sequestration in the growing stock of trees in Finland is dependent on the forest management and increased production potential due to climate change. This was analysed for the period 2003-2053 using forest inventory data and the forestry model MELA. Four combinations of two climate change and two management scenarios were studied: current (CU) and gradually warming (CC) climate and forest management strategies corresponding to diVerent rates of utilisation of the cutting potential, namely maximum sustainable removal (Sust) or maximum net present value (NPV) of wood production (Max). In this analysis of Finland, the initial amount of carbon in the growing stock was 765 Mt (2,802 Tg CO 2 ). At the end of the simulation, the carbon in the growing stock of trees in Finland had increased to 894 Mt (3,275 Tg CO 2 ) under CUSust, 906 Mt (3,321 Tg CO 2 ) under CUMax, 1,060 Mt (3,885 Tg CO 2 ) under CCSust and 1,026 Mt (3,758 Tg CO 2 ) under CCMax. The results show that future development of carbon in the growing stock is not only dependent on climate change scenarios but also on forest management. For example, maximising the NPV of wood production without sustainability constraints results, over the short term, in a large amount of wood obtained in regeneration cuttings and a consequent decrease in the amount of carbon in growing stock. Over the longer term, this decrease in the carbon of growing stock in regenerated forests is compensated by the subsequent increase in fast-growing young forests. By comparison, no drastic short-term decrease in carbon stock was found in the Sust scenarios; only minor decreases were observed.

Using the Finnish MELA model, a set of scenarios were produced and used to map the possibilities and risks surrounding the utilisation of peatlands in wood production in Finland. One of the scenarios was an estimate of allowable-cut calculated by maximising the net present value of the future revenues using a four per cent interest rate subject to non-decreasing flow of wood, saw logs and net income over a 50-year period, and net present value after the 50 year period greater or equal than in the beginning. The estimate for maximum regionally sustained removal in 1996-2005 was 68 million m 3 per year -approaching 74 million m 3 during the next decades. In this scenario, 14 per cent of all cuttings during the period 1996-2005 would be made on peatlands, which comprise ca. 31 per cent of the total area of forestry land. By the year 2025, the proportion of peatland cuttings would increase to over 20 per cent. The increase in future cutting possibilities on peatlands compensated for a temporary decrease in cuttings and growing stock on mineral soils. The allowable-cut effect was especially pronounced in northern Finland, where peatlands play an important role in wood production. In addition, the sensitivity of cutting possibilities for assumptions related to growth and price were analysed. The estimate of maximum sustainable yield as defined here seems to be fairly robust on the whole, except in northern Finland where the cutting scenarios were sensitive to the changes in the price of birch pulpwood. The proportion of peatland stands that are profitable for timber production depends on the interest rate: the higher the rate of interest the less peatland stands are thinned. The effect of cutting profile on future logging conditions and resulting costs were analysed in two forestry centres. If clear cuttings on mineral soils are to be cut first, an increase in future logging costs is inevitable.

The purpose of this study was to optimize forest management for a forest region (the total area of forest and scrub land 1.54 mill. ha) under changing climate by using the large-scale forestry scenario model MELA and sample plot data from the geo-referenced National Forest Inventory (NFI). The MELA model is based on integrated simulation and optimisation; in the simulation it utilises empirical tree-level models into which the impacts of climate change were introduced by transfer variables derived by using the physiological model FinnFor. Six scenarios with differences in climate and forest management were defined. In simulations, the accelerating tree growth caused by climate change resulted in an increase in maximum sustainable removal of trees at regional level. Changes in regionally optimized forest management were also detected during the analysis period of 30 years; the proportion of thinnings increased because the stands fulfilled the thinning requirements earlier than in the current climate. This study was the first attempt to solve endogenously maximum sustainable timber production and corresponding forest management at the regional level under different climate scenarios. When implemented in the MELA system, which is widely used in Finnish forestry, the transfer variables offer means of disseminating the results from physiological studies to planning of adjustment and mitigation measures under changing climate.