• Energy Research

Forests are the dominant land cover in Nordic–Baltic countries, and forestry, the management of forests for improved ecosystem-service (ES) delivery, is an important contributor to sustainability. Forests and forestry support multiple United Nations Sustainability Goals (UN SDGs) and a number of EU policies, and can address conflicting environmental goals. Forests provide multiple ecosystem services and natural solutions, including wood and fibre production, food, clear and clean water and air, animal and plant habitats, soil formation, aesthetics, and cultural and social services. Carbon sequestered by growing trees is a key factor in the envisaged transition from a fossil-based to a biobased economy. Here, we highlight the possibilities of forest-based solutions to mitigate current and emerging societal challenges. We discuss forestry effects on forest ecosystems, focusing on the optimisation of ES delivery and the fulfilment of UN SDGs while counteracting unwanted effects. In particular, we highlight the trilemma of (i) increasing wood production to substitute raw fossil materials, (ii) increasing forest carbon storage capacity, and (iii) improving forest biodiversity and other ES delivery.

Abstract During the autumn, plants undergo a physiological process of cold hardening to limit damage caused by the low temperatures of winter. Under a warming climate, plants may be less cold hardened and hence more susceptible to the effects of a sudden temperature drop. During the growth season of 2010–2011, growth and cold hardening of European aspen ( Populus tremula L.) seedlings from native wild populations were examined under ambient and projected climate scenarios in greenhouses at the Haapastensyrja research station in Southern Finland. Using locally obtained seedlings, we manipulated temperature and soil moisture during the normal growth period and then subjected them to an artificial freezing treatment during September–November 2010. At the end of the experiment, we determined seedling height, survival and the extent of stem damage, and analysed their variation with mixed effect models. Among the treatments tested, temperature was the main factor affecting survival, cold hardening, and frost damage to seedlings. The higher temperature (4 °C increase) of the 2100 future climate regime was associated with a 35% decrease in seedling survival (from 66 to 31%) during the growing period. Increased irrigation had a positive, but considerably weaker effect on seedling survival (improved survival by ca. 8%). Height of seedlings after the first growth season was enhanced by increased soil moisture and temperature, but these effects were negated the following spring by increased frost damage caused by warmer growth conditions. Although cold hardiness increased as the season progressed, increase of temperature by 1 and 4 °C severely diminished it, and survival after the freezing dropped from 55% (control) to 48% and 14%, while stem damage increased from 58% (control) to 90% and 96%, respectively. These results suggest that regeneration of north European aspen might become burdened in a warmer climate. Although survival was clearly affected, several seedlings grown under the future climate regimes survived freezing and overwintered with negligible damage, suggesting an adaptive capacity of the local population. The intraspecific competition that occurred as a side effect of the experimental setup also affected cold hardening, suggesting that stand structure might be managed to improve the resilience of aspen to frost damage.

Forest ecosystems are significant carbon pools on a global scale, and also a source of renewable raw materials. Moreover, the European Union (EU) aims to tackle climate change and reach climate neutrality; therefore, forest regulations are designed to promote sustainable forest management practices and ensure the long-term health and productivity of forests. It is important to balance regulatory requirements with the economic, social, and environmental needs of forest stakeholders. This study analyses four theoretical scenarios (business as usual, green deal, intensive forestry, and intensive forestry with afforestation) and prognoses the management impact on standing volume and carbon stock in living trees and harvested wood products (HWPs). Thus, the aim of this study is to evaluate different theoretical forest management scenarios to predict changes in standing volume and carbon stock in living tree biomass and HWPs for the 100 next years. The results suggest that intensive targeted forestry practices may enhance carbon sequestration and were found to be the most suitable strategy for Latvia’s hemiboreal zone, as they balance economic benefits with carbon sequestration and ecosystem services. The obtained results can be valuable for policymakers and forest managers to promote sustainability and balance the diverse needs of society and forest stakeholders.

12 Pág. Mixed forests are suggested as a strategic adaptation of forest management to climate change. Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) are tree species of high economic and ecological value for European forestry. Both species coexist naturally in a large part of their distributions but there is a lack of knowledge on the ecological functioning of mixtures of these species and how to manage such stands. This paper analyses these species’ intra- and inter-specific competition, including size-symmetric vs. size-asymmetric competition, and explore the effect of weather conditions on tree growth and competition. We studied basal area growth at tree level for Scots pine and Norway spruce in mixed versus pure stands in 22 triplets of fully-stocked plots along a broad range of ecological conditions across Europe. Stand inventory and increment cores provided insights into how species mixing modifies tree growth compared with neighbouring pure stands. Five different competition indices, weather variables and their interactions were included and checked in basal area growth models using a linear mixed model approach. Interspecific size-asymmetric competition strongly influenced growth for both tree species, and was modulated by weather conditions. However, species height stratification in mixed stands resulted in a greater tree basal area growth of Scots pine (10.5 cm2 year−1) than in pure stands (9.3 cm2 year−1), as this species occupies the upper canopy layer. Scots pine growth depended on temperature and drought, whereas Norway spruce growth was influenced only by drought. Interspecific site-asymmetric competition increased in cold winters for Scots pine, and decreased after a drought year for Norway spruce. Although mixtures of these species may reduce tree size for Norway spruce, our results suggest that this could be offset by faster growth in Scots pine. How inter-specific competition and weather conditions alter tree growth may have strong implications for the management of Scots pine-Norway spruce mixtures along the rotation period into the ongoing climate change scenario. The networking of this study was supported by the REFORM project (number FR-2017/0001, Resilience of forest mixtures: Mixed Species forest management. Lowering risk, increasing resilience) from the ERA-Net Sumforest. We thank national funders of REFORM project (Spanish Ministry of Science and Innovation: PCIN2017-026, Research Council of Lithuania (LMTLT) S-SUMFOREST-17-1, Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS) FR-2017/0001) and those funders for the support to non-participants in the REFORM project (Denmark: Contract between Danish Ministry of Environment and Food and Department of Geosciences and Natural Resource Management of UCPH; Estonia: Estonian University of Life Sciences projects number P180024MIME and P200029MIME; Poland: EU CARE4C project (GA 778322) supported by the Polish Government MNiSW2018-2021 matching fund (W117/H2020/2018); Slovakia: APVV-15-0265). We also thank to all national project partners and forest owners who allowed us to establish and measure the triplets in this study. Peer reviewed

Climate change manifests itself as a change in the probability of extreme weather events, and it is projected that windstorms will become more frequent and intense in Northern Europe. Additionally, the frequency and length of warm periods with wet, unfrozen soil in winter will rise in this region. These factors will lead to an increased risk of storm damages in forests. Factors affecting trees’ resistance to wind uprooting have been well quantified for some species but not for a common and economically important tree, the silver birch (Betula pendula Roth.). Therefore, this study aimed to assess the root-soil plate characteristics of silver birch on wet and dry mineral soils in hemiboreal forests. The root-soil plate and aboveground parameters were measured for 56 canopy trees uprooted in destructive, static-pulling experiments. The shape of the root-soil plate corresponds to the elliptic paraboloid. A decreasing yet slightly different trend was observed in root depth distribution with increasing distance from the stem in both soils. The main factors determining root-soil plate volume were width, which was notably larger on wet mineral soils, and tree diameter at breast height. Consequently, the root-soil plate volume was significantly larger for trees growing on wet mineral soils than for trees growing on dry soils, indicating a wind adaptation.