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Uncertainties are essential, yet often neglected, information for evaluating the reliability in forest carbon balance projections used in national and regional policy planning. We analysed uncertainties in the forest net biome exchange (NBE) and carbon stocks under multiple management and climate scenarios with a process-based ecosystem model. Sampled forest initial state values, model parameters, harvest levels and global climate models (GCMs) served as inputs in Monte Carlo simulations, which covered forests of the 18 regions of mainland Finland over the period 2015-2050. Under individual scenarios, the results revealed time- and region-dependent variability in the magnitude of uncertainty and mean values of the NBE projections. The main sources of uncertainty varied with time, by region and by the amount of harvested wood. Combinations of uncertainties in the representative concentration pathways scenarios, GCMs, forest initial values and model parameters were the main sources of uncertainty at the beginning, while the harvest scenarios dominated by the end of the simulation period, combined with GCMs and climate scenarios especially in the north. Our regionally explicit uncertainty analysis was found a useful approach to reveal the variability in the regional potentials to reach a policy related, future target level of NBE, which is important information when planning realistic and regionally fair national policy actions., (© 2023. The Author(s).)

Forest management methods and harvest intensities influence wood production, carbon sequestration and biodiversity. We devised different management scenarios by means of stakeholder analysis and incorporated them in the forest growth simulator PREBAS. To analyse impacts of harvest intensity, we used constraints on total harvest: business as usual, low harvest, intensive harvest and no harvest. We carried out simulations on a wall-to-wall grid in Finland until 2050. Our objectives were to (1) test how the management scenarios differed in their projections, (2) analyse the potential wood production, carbon sequestration and biodiversity under the different harvest levels, and (3) compare different options of allocating the scenarios and protected areas. Harvest level was key to carbon stocks and fluxes regardless of management actions and moderate changes in proportion of strictly protected forest. In contrast, biodiversity was more dependent on other management variables than harvesting levels, and relatively independent of carbon stocks and fluxes., (© 2023. The Author(s).)

We present regionally aggregated emissions of greenhouse gases (GHG) from five land cover categories in Finland: artificial surfaces, arable land, forest, waterbodies, and wetlands. Carbon (C) sequestration to managed forests and unmanaged wetlands was also assessed. Models FRES and ALas were applied for emissions (CO 2 , CH 4 , N 2 O) from artificial surfaces and agriculture, and PREBAS for forest growth and C balance. Empirical emission coefficients were used to estimate emissions from drained forested peatland (CH 4 , N 2 O), cropland (CO 2 ), waterbodies (CH 4 , CO 2 ), peat production sites and undrained mires (CH 4 , CO 2 , N 2 O). We calculated gross emissions of 147.2 ± 6.8 TgCO 2 eq yr -1 for 18 administrative units covering mainland Finland, using data representative of the period 2017-2025. Emissions from energy production, industrial processes, road traffic and other sources in artificial surfaces amounted to 45.7 ± 2.0 TgCO 2 eq yr -1 . The loss of C in forest harvesting was the largest emission source in the LULUCF sector, in total 59.8 ± 3.3 TgCO 2 eq yr -1 . Emissions from domestic livestock production, field cultivation and organic soils added up to 12.2 ± 3.5 TgCO 2 eq yr -1 from arable land. Rivers and lakes (13.4 ± 1.9 TgCO 2 eq yr -1 ) as well as undrained mires and peat production sites (14.7 ± 1.8 TgCO 2 eq yr -1 ) increased the total GHG fluxes. The C sequestration from the atmosphere was 93.2 ± 13.7 TgCO 2 eq yr -1 . with the main sink in forest on mineral soil (79.9 ± 12.2 TgCO 2 eq yr -1 ). All sinks compensated 63% of total emissions and thus the net emissions were 53.9 ± 15.3 TgCO 2 eq yr -1 , or a net GHG flux per capita of 9.8 MgCO 2 eq yr -1 ., (© 2023. The Author(s).)