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We investigated the interaction between fungal communities of soil and dead wood substrates. For this, we applied molecular species identification and stable isotope tracking to both soil and decaying wood in an unmanaged boreal Norway spruce-dominated stand. Altogether, we recorded 1990 operational taxonomic units, out of which more than 600 were shared by both substrates and 589 were found to exclusively inhabit wood. On average the soil was more species-rich than the decaying wood, but the species richness in dead wood increased monotonically along the decay gradient, reaching the same species richness and community composition as soil in the late stages. Decaying logs at all decay stages locally influenced the fungal communities from soil, some fungal species occurring in soil only under decaying wood. Stable isotope analyses suggest that mycorrhizal species colonising dead wood in the late decay stages actively transfer nitrogen and carbon between soil and host plants. Most importantly, Piloderma sphaerosporum and Tylospora sp. mycorrhizal species were highly abundant in decayed wood. Soil- and wood-inhabiting fungal communities interact at all decay phases of wood that has important implications in fungal community dynamics and thus nutrient transportation.

Land-based mitigation measures are needed to achieve climate targets. One option is the mitigation of currently high greenhouse gas (GHG) emissions of nutrient-rich drained peatland forest soils. Continuous cover forestry (CCF) has been proposed as a measure to manage this GHG emission source; however, its emission reduction potential and impact on timber production at regional and national scales have not been quantified. To quantify the potential emission reduction, we simulated four management scenarios for Finnish forests: (i) The replacement of clear-cutting by selection harvesting on nutrient-rich drained peatlands (CCF) and (ii) the current forest management regime (BAU), and both at two harvest levels, namely (i) the mean annual harvesting (2016–2018) and (ii) the maximum sustainable yield. The simulations were conducted at the stand scale with a forest simulator (MELA) coupled with a hydrological model (SpaFHy), soil C model (Yasso07) and empirical GHG exchange models. Simulations showed that the management scenario that avoided clear-cutting on nutrient-rich drained peatlands (i.e. CCF) produced approximately 1 Tg CO 2 eq. higher carbon sinks annually compared with BAU at equal harvest level for Finland. This emission reduction can be attributed to the maintenance of a higher biomass sink and to the mitigation of soil emissions from nutrient-rich drained peatland sites.

Summary Microbial respiration in dead wood contributes substantially to the long‐lived forest carbon (C) pool and has a significant role in the forest nitrogen (N) cycle. Wood N content has been found to increase during the decay process; however, temporal dynamics and the sources of this external N remain unclear. To examine N dynamics at various stages of decomposition, we combined high variety of analytical methods on Norway spruce logs, including wood δ15N, N%, 14C‐dating, fungal composition and N2 fixation rate. For N2 fixation rate, we also determined its dependency on ambient temperature and decay class, when estimating annual N2 fixation rates for our study site. N2 fixation was observed to have a major role in increasing wood N content during decay. For the most decayed wood, it accounted for 60% of the total N accumulation. Compared to other reports, where the annual temperature was similar to our site, the calculated annual fixation rate of 85 g N ha−1 year−1 is a low estimate. However, previous studies have not taken appropriately into account the dependency of N2 fixation rate on ambient temperature and decay class. Our δ15N model describing the sources of external N, statistical analysis and the fungal DNA composition of decayed wood suggest that other sources of external N accumulating in wood were soil‐foraging wood‐decay fungi and mycorrhizal fungi. Our study improves knowledge of the temporal dynamics of N accumulation in wood with advancing wood decay, the potential sources of external N and their relative significance. All of these factors are important for nitrogen as well as carbon models dealing with ecosystem responses to climate change. Lay Summary

Rotation forestry based on clear-cut harvesting, site preparation, planting and intermediate thinnings is currently the dominant management approach in Fennoscandia. However, understanding of the greenhouse gas (GHG) emissions following clear-cutting remains limited, particularly in drained peatland forests. In this study, we report eddy-covariance-based (EC-based) net emissions of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) from a fertile drained boreal peatland forest 1 year after wood harvest. Our results show that, at an annual scale, the site was a net CO2 source. The CO2 emissions dominate the total annual GHG balance (23.3 t CO2eq. ha−1 yr−1, 22.4–24.1 t CO2eq. ha−1 yr−1, depending on the EC gap-filling method; 82.0 % of the total), while the role of N2O emissions (5.0 t CO2eq. ha−1 yr−1, 4.9–5.1 t CO2eq. ha−1 yr−1; 17.6 %) was also significant. The site was a weak CH4 source (0.1 t CO2eq. ha−1 yr−1, 0.1–0.1 t CO2eq. ha−1 yr−1; 0.4 %). A statistical model was developed to estimate surface-type-specific CH4 and N2O emissions. The model was based on the air temperature, soil moisture and contribution of specific surface types within the EC flux footprint. The surface types were classified using unoccupied aerial vehicle (UAV) spectral imaging and machine learning. Based on the statistical models, the highest surface-type-specific CH4 emissions occurred from plant-covered ditches and exposed peat, while the surfaces dominated by living trees, dead wood, litter and exposed peat were the main contributors to N2O emissions. Our study provides new insights into how CH4 and N2O fluxes are affected by surface-type variation across clear-cutting areas in forested boreal peatlands. Our findings highlight the need to integrate surface-type-specific flux modelling, EC-based data and chamber-based flux measurements to comprehend the GHG emissions following clear-cutting and regeneration. The results also strengthen the accumulated evidence that recently clear-cut peatland forests are significant GHG sources.

The natural world is under unprecedented and accelerating pressure. Much work on understanding resilience to local and global environmental change has, so far, focussed on ecosystems. However, understanding a system’s behaviour requires knowledge of its component parts and their interactions. Here we call for increased efforts to understand ‘biological resilience’, or the processes that enable components across biological levels, from genes to communities, to resist or recover from perturbations. Although ecologists and evolutionary biologists have the tool-boxes to examine form and function, efforts to integrate this knowledge across biological levels and take advantage of big data (e.g. ecological and genomic) are only just beginning. We argue that combining eco-evolutionary knowledge with ecosystem-level concepts of resilience will provide the mechanistic basis necessary to improve management of human, natural and agricultural ecosystems, and outline some of the challenges in achieving an understanding of biological resilience.

We present a new application of terrestrial laser scanning and mathematical modelling for the quantitative change detection of tree biomass, volume, and structure. We investigate the feasibility of the approach with two case studies on trees, assess the accuracy with laboratory reference measurements, and identify the main sources of error, and the ways to mitigate their effect on the results. We show that the changes in the tree branching structure can be reproduced with about ±10% accuracy. As the current biomass detection is based on destructive sampling, and the change detection is based on empirical models, our approach provides a non-destructive tool for monitoring important forest characteristics without laborious biomass sampling. The efficiency of the approach enables the repeating of these measurements over time for a large number of samples, providing a fast and effective means for monitoring forest growth, mortality, and biomass in 3D.

Nutrient availability affects microbial respiration kinetics; their sensitivities to environmental conditions; and, thus, the soil organic carbon (SOC) stocks. We examined long-term nitrogen (N) addition effects on soil heterotrophic respiration (Rh), methane (CH4) oxidation, and nitrous oxide (N2O) emissions in an N-limited boreal Scots pine (Pinus sylvestris) forest in central Finland. Measurements included the following (in both control and N-fertilized plots): long-term tree biomass monitoring (1960–2020); soil organic carbon (SOC) monitoring in 2023; monthly aboveground litterfall monitoring (2021–2023); biweekly CO2, CH4, and N2O fluxes during the 2021–2023 growing seasons; and quarter-hourly recordings of soil temperature (T) and soil water content (SWC). We assessed mean greenhouse gas (GHG) flux differences and Rh dependence on T and SWC using polynomial and nonlinear regression models. Tree biomass, litterfall, and SOC increased with long-term N fertilization. However, N fertilization also significantly increased mean Rh, reduced CH4 oxidation slightly, and modestly raised N2O emissions. SOC-normalized Rh (Rh/SOC) did not significantly differ between treatments, yet relationships between Rh/SOC and T and SWC diverged with fertilization. In control plots, Rh/SOC peaked at 15.8 °C, whereas it peaked at 16.8 °C in N-fertilized plots. Under N fertilization conditions, Rh/SOC was weakly SWC-dependent, contrasting with a distinct humped SWC response enhancing annual Rh/SOC in control plots. Annually, N-fertilized plots respired 10.3 % of SOC (±0.3 SE, standard error), compared to 12.2 % (±0.5 SE) in control plots, suggesting that N fertilization promoted SOC retention. Consequently, N fertilization reduced average annual net CO2 emissions by 345.4 (±73.6 SE) gCO2m-2yr-1, while the combined effects on CH4 and N2O fluxes and the production energy of N fertilizer contributed a minor CO2-equivalent increase of 17.7 (±0.5 SE) gCO2eq.m-2yr-1. In conclusion, long-term N fertilization in boreal forests could reduce the global warming potential of soil GHG emissions, mainly by slowing Rh/SOC and altering its responses to T and SWC, thereby enhancing SOC sequestration in addition to the increased tree biomass carbon sink.

Tree seedlings are produced in tree nurseries. However, nursery-grown seedlings often exhibit poor performance after outplanting due to the lack of adaptation to harsh natural conditions. These nursery-grown seedlings do not necessarily possess well-developed ectomycorrhizal symbionts, which help to obtain nutrients and increase resilience in exchange for seedling photoassimilated carbon. To improve the quality of the seedlings in natural conditions, we sowed spruce seeds on growing media with the addition of wood chips, i.e. stemwood chips or polyphenol- and resin acid-rich knotwood chips. Wood chips were chosen because they are common forest side-streams, and their compounds have shown a potential to improve mycorrhization and seedling fitness. Wood chips initially decreased the growth of seedlings. However, this effect levelled off with time and depended on the quality of the wood. Wood chips had no effect on mycorrhization. Further testing of the wood material showed that wood chips seemed to decrease seedling growth via nitrogen (N) immobilisation rather than a direct toxic effect. The phenomenon of N immobilisation on wood chips could be explored further to develop a slow-release N source, aptly reflecting N availability in natural conditions. Slow-release N source based on wood chips could be beneficial both to increase survival in natural conditions and for environment protection.

Ditches of forestry-drained peatlands are an important source of methane (CH 4 ) to the atmosphere. These CH 4 emissions are currently estimated using the IPCC Tier 1 emission factor (21.7 g CH 4 m −2  y −1 ), which is based on a limited number of observations (11 study sites) and does not take into account that the emissions are affected by the condition and age of the ditches. Furthermore, the total area of different kinds of ditches remains insufficiently estimated. To construct more advanced ditch CH 4 emission factors for Finland, we measured CH 4 emissions in ditches of 3 forestry-drained peatland areas (manual chamber technique) and amended this dataset with previously measured unpublished and published data from 18 study areas. In a predetermined 2-type ditch classification scheme, the mean CH 4 emissions (±standard error) were 2.6 ± 0.8 g CH 4 m −2  y −1 and 20.6 ± 7.0 g CH 4 m -2  y −1 in moss-covered and moss-free ditches, respectively. In a more detailed 4-type classification scheme, the yearly emissions were 0.6 ± 0.3, 3.8 ± 1.1, 8.8 ± 3.2, and 25.1 ± 9.7 g CH 4 m −2  y −1 in Sphagnum -covered, Sphagnum - and vascular plant—covered, moss-free and vascular plant-covered, and plant - free ditches, respectively. Hence, we found that Tier 1 emission factor may overestimate ditch CH 4 emissions through overestimation of the emissions of moss-covered ditches, irrespective of whether they harbor potentially CH 4 conducing vascular plants. Based on the areal estimates and the CH 4 emission factors for moss-covered and moss-free ditches, CH 4 emissions of ditches of forestry-drained peatlands in Finland were 8,600 t a −1 , which is 63% lower than the current greenhouse gas inventory estimates for ditch CH 4 emissions (23,200 t a −1 ). We suggest that the Tier 1 emission factor should be replaced with more advanced emission factors in the estimation of ditch CH 4 emissions of boreal forestry-drained peatlands also in other countries than in Finland. Furthermore, our results suggest that the current practice in Finland to minimize ditch-network maintenance by ditch cleaning will likely decrease CH 4 emissions from ditches, since old moss-covered ditches have very low emissions.

This study investigates the carbon offset potential in Espoo, Finland, by comparing a construction-impacted deforestation site with a larger conserved forest area. Addressing a knowledge gap in localized forest conservation as a CO 2 offset method, our research quantifies the carbon stock and sequestration impacts under both baseline and alternative scenarios for the two study sites. The baseline scenario for offset site reflects standard forest management practices, while the alternative scenario involves complete forest conservation without active management. Our findings reveal that the conserved forest (79 ha), dominated by Norway spruce (Picea abies) and Scots pine (Pinus sylvestris), increased its carbon stock by 26 Mg C ha −1 in soil and 65 Mg C ha −1 in biomass. This enhancement is sufficient to compensate for the smaller deforestation site’s (19 ha), also containing a mix of Norway spruce and Scots pine, stock loss of 186 Mg C ha −1 in soil and 43 Mg C ha −1 in biomass. Furthermore, this study illuminates the complexities of CO 2 compensation regulation and emphasizes the necessity for robust, transparent carbon accounting practices. The insights offer a valuable perspective on integrating nature-based solutions in urban planning to achieve broader ecological and climate goals.