Search

Bioenergy from forest residues can be used to substitute fossil energy sources and reduce carbon emissions. However, increasing biomass removals from forests reduce carbon stocks and carbon input to litter and soil. The magnitude and timeframe of these changes in the forest carbon balance largely determine how effectively forest biomass reduces greenhouse gas emissions from the energy sector and helps to mitigate climate change. This paper reviews the impacts of harvest-residue-based bioenergy on the carbon balance of forests and discusses aspects linked to the concept of carbon neutrality. This type of forest bioenergy will reduce the emissions in a long run but near-term reductions depend essentially on the longevity of the residues used. [Copyright &y& Elsevier]

Abstract: Forest soils store large amounts of carbon (C), and releases of C from this pool may significantly increase the CO2 concentration in the atmosphere. Organic matter decomposition in soils has been shown to strongly depend on temperature and soil moisture and is, therefore, susceptible to the climate change. Reliable methods are needed to monitor and predict the changes in soil C stocks. In this study, we tested the Yasso07 soil C model by comparing the model predictions to repeated soil C measurements of organic layer and, furthermore, to the estimates of two other C models, namely Yasso and ROMUL. In the model simulations, we used the litter input time series derived from forest biomass estimates based on the national forest inventories. Both the repeated empirical measurements and Yasso07 simulations indicated upland forest soils to be small sinks of C in Southern Finland. The Yasso07 model was able to predict both soil C stock and C accumulation within the error limits of the measured values. Yasso07 and the earlier version, Yasso, predicted very similar soil C stocks close to the measured values, but slightly underestimated C accumulation. The annual soil C changes predicted by the Yasso07 and ROMUL models were reasonably close to each other, even though the models are based on a very different basic structure. However, the differences in the model predictions were at the highest in years with the highest precipitation, indicating that there are still uncertainties in predicting the effects of soil moisture on the soil C stock changes. [Copyright &y& Elsevier]

Abstract: The growing stock more than doubled from 1.6 to 3.4millionm3 between 1912 and 2005 in forests on an area of 387km2 in southern Finland. The stock expansion continued for 93 years noting interim results, which were available for 1959, 1982, 1994 and 1999. Forested area in the region hardly changed. Carbon sequestration was mainly a result of a long-term recovery from forest degradation, a legacy of land use in the 18th and 19th centuries. Tree demography responded to management change especially of mature stands: Average tree size and stocking density of stands increased. On average the expanding biomass stock sequestered 18tons C annually per km2 (18g C per m2). In comparison, the emissions of fossil carbon in the region were estimated at 12tons C per km2 (12g C per m2) on average. However, fossil CO2 emissions exceeded biomass sequestration in recent decades. The powerful and persistent expansion of the carbon stock was an unintended co-benefit of forestry, which was motivated by the intention to improve timber yield. On the more negative side the change in management introduced clear-cuts, and a loss of diverse elements of the pre-industrial biota. [Copyright &y& Elsevier]

Abstract: Growing stocks of trees in Europe have increased in a magnitude that is significant in terms of carbon (C) sink strength. Estimates of the soil C sink strength that this increased stock of trees may have induced on a regional scale are scarce, uncertain and difficult to compare. This illustrates the need for a widely applicable calculation method. Here, we calculate a C budget of productive forest in southeast Norway based on forest inventory information, biomass expansion factors (BEF), biomass turnover rates and the dynamic soil model Yasso. We estimate a 29% increase (112–145Tg) of C in biomass between 1971 and 2000, and estimate the associated increase of C in soils (including dead wood) to be 4.5% (181–189Tg). The C sink strengths in biomass and soils (including dead wood) in 1990 are 0.38 and 0.08Mgha−1 yr−1, respectively. Estimated soil C density is 58MgCha−1 or ca 40% of measured soil C density in Norwegian forest soils. A sensitivity analysis – using uncertainty estimates of model inputs and parameters based on empirical data – shows that the underestimation of the soil C stock can be due to overestimation of decomposition rates of recalcitrant organic matter in the soil model and to including only trees as a source of litter. However, uncertainty in these two factors is shown to have a minimal effect on soil sink estimates. The key uncertainty in the soil sink is the initial value of the soil C stock, i.e. the assumed steady state soil C stock at the start of the time series in 1970. However, this source of uncertainty is reduced in importance for when approaching the end of the data series. This indicates that a longer time series of forest inventory data will decrease the uncertainty in the soil sink estimate due to initialisation of the soil C stock. Other, less significant, sources of uncertainty in estimates of soil stock and sink are BEF for fine roots and turnover rates of fine roots and foliage. The used method for calculation of a forest C budget can be readily applied to other regions for which similar forest resource data are available. [Copyright &y& Elsevier]

Abstract: The effects of three forest management alternatives on stand development were simulated using the MOTTI stand simulator, a stand-level analysis tool developed for multiple-purpose forestry planning. The simulation results were used to analyse the effects of different management schedules on wood production, profitability, carbon sequestration and biodiversity. Stand data from a 35-year-old Norway spruce (Picea abies (L.) Karst.) dominated stand with a deciduous admixture were used as the starting point. Stand development was simulated for a period of 35 years, and additionally for 65 years for biodiversity analyses. The three management alternatives were—(1) pure spruce stand: two commercial thinnings with removal of deciduous admixture, regeneration at 70 years, goal to maximize wood production; (2) mixed stand: as the previous one, but the deciduous admixture was maintained throughout the rotation, goal to enhance biodiversity; (3) unmanaged: no treatments. The pure and mixed alternatives including commercial thinnings outperformed the unmanaged one both in the production of merchantable wood and in profitability (value of standing stock for the unmanaged alternative), but did not notably differ from each other. Carbon sequestration was directly proportional to biomass production and thus highest in the unmanaged alternative. The mixed stand had a 50%, and unmanaged stand 88% higher species richness than the pure stand at the age of 70 years. Prolonging the rotation to 100 years also considerably increased the species richness. The applicability of the results and use of the MOTTI simulator in forestry planning are discussed. [Copyright &y& Elsevier]

Elongation of rotation length is a forest management activity countries may choose to apply under Article 3.4 of the Kyoto Protocol to help them meet their commitments for reduction of greenhouse gas emissions. We used the CO2FIX model to analyze how the carbon stocks of trees, soil and wood products depend on rotation length in different European forests. Results predicted that the carbon stock of trees increased in each forest when rotation length was increased, but the carbon stock of soil decreased slightly in German and Finnish Scots pine forests; the carbon stock of wood products also decreased slightly in cases other than the Sitka spruce forest in UK. To estimate the efficiency of increasing rotation length as an Article 3.4 activity, we looked at changes in the carbon stock of trees resulting from a 20-year increase in current rotation lengths. To achieve the largest eligible carbon sink mentioned in Article 3.4 of the Kyoto Protocol, the rotation lengths need to be increased on areas varying from 0.3 to 5.1 Mha depending on the forest. This would in some forests cause 1–6% declines in harvesting possibilities. The possible decreases in the carbon stock of soil indicate that reporting the changes in the carbon stocks of forests under Article 3.4 may require measuring soil carbon. [Copyright &y& Elsevier]

The soils of western European forests may be accumulating carbon, because tree biomass has been expanding in these forests already for decades, and the more numerous and larger trees can produce more litter. We calculated the carbon budget of soils and trees in the forests of 14 EU countries plus Norway and Switzerland from 1950 to 2040 by integrating forest resource information (inventory data from 1950 to 1990 and a forest resource forecast from 2000 to 2040), biomass allocation and turnover information, and a dynamic soil carbon model.The carbon stock of the soils increased throughout the studied period. In 1990, the soil carbon sink was 26 Tg per year. This is 32 or 48% compared with our two estimates of the tree carbon sink for that year. Until 2040, the soil carbon sink was estimated to increase to 43 Tg per year. This would already be 61 or 69% compared with the tree carbon sink that year.In 1990, the soils contributed most to the total forest carbon sink in central Europe, where the soil carbon sink was almost as large as the tree carbon sink. The soils were least important in southern Europe, where the soil carbon sink was less than 25% compared with the tree carbon sink. In the future, the contribution of the soils to the total forest carbon sink was estimated to increase everywhere except in southern Europe.The soil carbon stocks increased mainly because litter fall from living trees increased while the other sources of soil carbon, i.e. the residues of harvests and natural disturbances, varied less. This litter fall was also the largest source of soil carbon accounting for 70–80% of the total. The soil carbon stocks in these forests could thus be most effectively controlled by forest management actions, such as the choices of harvest regimes or tree species, which especially affect the litter production of living trees.According to an uncertainty analysis, we may have overestimated the soil carbon sink by 35% or underestimated it by 50% throughout the studied period. The largest uncertainties were related to calculating the litter production of living trees and decomposition in soil. [Copyright &y& Elsevier]

The increasing concentration of greenhouse gases in the atmosphere and the consequent warming of the Earth’s surface presents a threat to the environment and economic development. This paper discusses how regional level impacts of transient climate change on forest growth are assessed with process-based models and how these responses are then scaled up to country and European level using national forest inventory data in combination with the European forest information scenario (EFISCEN) model. Stem wood volume and increment in the EFISCEN model is converted to whole tree biomass based on information from process-based models. Calculation of carbon in soil and in wood products is included in this approach. A preliminary carbon budget under current and changing climatic conditions, with current management regime for Germany, is presented and discussed. Although carbon stocks in trees, soil and products are increasing, we found that the German forest sector can sustain a carbon sink until 2050, but the sink gradually becomes smaller, declining from 1.7 Mg C/ha per year in 1995 to 0.7 Mg C/ha per year in 2050. This is due to ageing of forests, as sink activity in older forests is smaller than in younger forests. The sink activity in the soil increased slightly, but rate of storage in trees decreased more. Under changing climatic conditions, both carbon stock and sink activity in trees and soil were larger than under current climatic conditions.International processes, such as the United Nations Framework Convention on Climate Change (UNFCCC) and The Kyoto Protocol require integrated assessments of the role of forests and forestry on mitigation of climate change, but there is also a need for assessments of the impacts of climate change on forests. Research can provide information for decision-makers regarding the functioning of the system, potential risks and uncertainties. The upscaling approach described in this paper will be used later to investigate the impacts of selected forest management scenarios, under current and changing climatic conditions, on the forestry carbon budgets of 27 European countries. [Copyright &y& Elsevier]