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We used a process-based hydrological model SUSI to improve guidelines for ditch network maintenance (DNM) operations on drained peatland forests. SUSI takes daily weather data, ditch depth, strip width, peat properties, and forest stand characteristics as input and calculates daily water table depth (WTD) at different distances from ditch. The study focuses on Scots pine ( L.) dominated stands which are the most common subjects of DNM. Based on a literature survey, and consideration of the tradeoffs between forest growth and detrimental environmental impacts, long term median JulyâAugust WTD of 0.35 m was chosen as a target WTD. The results showed that ditch depths required to reach such WTD depends strongly on climatic locations, stand volume, ditch spacing, and peat thickness and type. In typical ditch cleaning areas in Finland with parallel ditches placed about 40 m apart and tree stand volumes exceeding 45 m ha, 0.3â0.8 m deep ditches were generally sufficient to lower WTD to the targeted depth of 0.35 m. These are significantly shallower ditch depths than generally recommended in operational forestry. The main collector ditch should be naturally somewhat deeper to permit water outflow. Our study brings a firmer basis on environmentally sound forestry on drained peatlands.Pinus sylvestris3â1

In Finland, the widespread drainage of boreal peatlands has led to increased forest productivity. The cost is a dramatic increase in soil greenhouse gas emissions. Empirical research of drained peatlands has found a correlation between greenhouse gas emissions and the ground water table. This suggests an opportunity to mitigate greenhouse gas emissions through forest management. We explore this opportunity at the landscape level through a simulation and optimization framework. We explore how forest management actions can impact the ground water table and the related greenhouse gas emissions. There are various economic and societal constraints for a set of forested peatland landscapes in Finland. First, we link forest simulations with hydrological and statistical models to predict C[O.sub.2], C[H.sub.4], and [N.sub.2]O emissions from the drained peatlands. We then present the range of landscape level solutions that prioritize between minimizing the net ecosystem greenhouse gas emissions, the economic timber value, and the even flow of timber income over time. Our results highlight the impact that integrating peatland soil greenhouse gas emissions will have on the planning process. This promotes the use of management options that benefit both biomass growth and reduced peatland soil greenhouse gas emissions. Key words: climate change mitigation, forest planning, optimization, boreal forests, Introduction Drained peatland forests are a major source of greenhouse gas (GHG) emissions in the boreal and temperate zones (Paavilainen and Paivanen 1995; Forsell et al. 2016). Their appropriate management [...]

As soil microbial respiration is the major component of land CO2 emissions, differences in the functional dependence of respiration on soil moisture among Earth system models (ESMs) contributes significantly to the uncertainties in their projections. Using soil organic C (SOC) stocks and CO2 data from a boreal forest–mire ecotone in Finland and Bayesian data assimilation, we revised the original precipitation-based monotonic saturation dependency of the Yasso07 soil carbon model using the non-monotonic Ricker function based on soil volumetric water content. We fit the revised functional dependency of moisture to the observed microbial respiration and SOC stocks and compared its performance against the original Yasso07 model and the version used in the JSBACH land surface model with a reduction constant for decomposition rates in wetlands. The Yasso07 soil C model coupled with the calibrated unimodal Ricker moisture function with an optimum in well-drained soils accurately reconstructed observed SOC stocks and soil CO2 emissions and clearly outperformed previous model versions on paludified organo-mineral soils in forested peatlands and water-saturated organic soils in mires. The best estimate of the posterior moisture response of decomposition used both measurements of SOC stocks and CO2 data from the full range of moisture conditions (from dry and xeric to wet and water-saturated soils). We observed unbiased residuals of SOC and CO2 data modelled with the moisture optimum in well-drained soils, suggesting that this modified function accounts more precisely for the long-term SOC change dependency according to ecosystem properties as well as the contribution of short-term CO2 responses including extreme events. The optimum moisture for decomposition in boreal forests was found in well-drained soils instead of the mid-range between dry and water-saturated conditions as is commonly assumed among soil C and ESMs. Although the unimodal moisture modifier with an optimum in well-drained soils implicitly incorporates robust biogeochemical mechanisms of SOC accumulation and CO2 emissions, it needs further evaluation with large-scale data to determine if its use in land surface models will decrease the uncertainty in projections. [ABSTRACT FROM AUTHOR]

Encroachment of vascular plants (VP) in temperate raised bogs, as a consequence of altered hydrological conditions and nutrient input, is widely observed. Effects of such vegetation shift on water and carbon cycles are, however, largely unknown and identification of responsible plant physiological traits is challenging. Process-based modelling offers the opportunity of gaining insights into ecosystem functioning beyond observations, and to infer decisive trait shifts of plant functional groups. We adapted the Soil–Vegetation–Atmosphere Transfer model pyAPES to a temperate raised bog site by calibration against measured peat temperature, water table and surface CO2 fluxes. We identified the most important traits determining CO2 fluxes by conducting Morris sensitivity analysis (MSA) under changing conditions throughout the year and simulated VP encroachment. We further investigated transferability of results to other sites by extending MSA to parameter ranges derived from literature review. We found highly variable intra-annual plant traits importance determining ecosystem CO2 fluxes, but only a partial shift of importance of photosynthetic processes from moss to VP during encroachment. Ecosystem respiration was dominated by peat respiration. Overall, carboxylation rate, base respiration rate and temperature sensitivity (Q10) were most important for determining bog CO2 balance and parameter ranking was robust even under the extended MSA. [ABSTRACT FROM AUTHOR]

Soil moisture plays a key role in soil nutrient and carbon cycling, plant productivity and in energy, water, and greenhouse gas exchanges between the land and the atmosphere. In this study, we used the Spatial Forest Hydrology (SpaFHy) model, in-situ soil moisture measurements and Sentinel-1 SAR-based soil moisture estimates to explore spatiotemporal controls of soil moisture in a subarctic headwater catchment in northwestern Finland. The role of groundwater dynamics and lateral flow on soil moisture was studied through three groundwater model conceptualizations: i) omission of groundwater storage and lateral flow, ii) conceptual TOPMODEL approach based on topographic wetness index, and iii) explicit 2D lateral groundwater flow. The model simulations were compared against continuous point-scale measurements, distributed manual measurements conducted in the study area, and novel SAR-based soil moisture estimates available from the area at high spatial and temporal resolution. Based on model scenarios and model-data comparisons, we assessed when and where the lateral groundwater flow shapes soil moisture, and under which conditions soil moisture variability is driven more by local ecohydrological processes, i.e. the balance of infiltration, drainage and evapotranspiration. The choice of groundwater conceptualization was shown to have a strong impact on the modeled soil moisture dynamics within the catchment. All model conceptualizations captured the observed soil moisture dynamics in the upland forests, but accounting for the lateral groundwater flow was necessary to reproduce the saturated conditions commonly occurring on the peatlands and occasionally on lowland forest grid-cells. We further highlight the potential of integrating multi-scale observations, including spatially explicit remote sensing data, with land surface and hydrological models. The results have broad implications for choosing suitable models for studying ecohydrological and biogeochemical processes as well as earth system feedbacks in subarctic and boreal environments. [ABSTRACT FROM AUTHOR]

Continuous cover forestry (CCF) has gained interest as an alternative to even-aged management particularly on drained peatland forests. However, relatively little is known about the physiological response of suppressed trees when larger trees are removed as a part of CCF practices. Consequently, studies concentrating on process-level modeling of the response of trees to selection harvesting are also rare. Here, we compared, modeled and measured harvest response of previously suppressed Norway spruce (Picea abies) trees to a selection harvest. We quantified the harvest response by collecting Norway spruce tree-ring samples in a drained peatland forest site and measuring the change in stable carbon and oxygen isotopic ratios of wood formed during 2010–20, including five post-harvest years. The measured isotopic ratios were compared with ecosystem-level process model predictions for |${\kern0em }^{13}$| C discrimination and |${\kern0em }^{18}$| O leaf water enrichment. We found that the model predicted similar but lower harvest response than the measurements. Furthermore, accounting for mesophyll conductance was important for capturing the variation in |${\kern0em }^{13}$| C discrimination. In addition, we performed sensitivity analysis on the model, which suggests that the modeled |${\kern0em }^{13}$| C discrimination is sensitive to parameters related to CO2 transport through stomata to the mesophyll. [ABSTRACT FROM AUTHOR]

The snowpack has a major influence on the land surface energy budget. Accurate simulation of the snowpack energy and radiation budget is challenging due to, e.g., effects of vegetation and topography, as well as limitations in the theoretical understanding of turbulent transfer in the stable boundary layer. Studies that evaluate snow, hydrology and land surface models against detailed observations of all surface energy balance components at high latitudes are scarce. In this study, we compared different configurations of the SURFEX land surface model against surface energy flux, snow depth and soil temperature observations from four eddy-covariance stations in Finland. The sites cover two different climate and snow conditions, representing the southern and northern subarctic zones, as well as the contrasting forest and peatland ecosystems typical for the boreal landscape. We tested different turbulent flux parameterizations implemented in the Crocus snowpack model. In addition, we examined common alternative approaches to conceptualize soil and vegetation, and we assessed their performance in simulating surface energy fluxes, snow conditions and soil thermal regime. Our results show that a stability correction function that increases the turbulent exchange under stable atmospheric conditions is imperative to simulate sensible heat fluxes over the peatland snowpacks and that realistic peat soil texture (soil organic content) parameterization greatly improves the soil temperature simulations. For accurate simulations of surface energy fluxes, snow and soil conditions in forests, an explicit vegetation representation is necessary. Moreover, we demonstrate the high sensitivity of surface fluxes to a poorly documented parameter involved in snow cover fraction computation. Although we focused on models within the SURFEX platform, the results have broader implications for choosing suitable turbulent flux parameterization and model structures depending on the potential use cases for high-latitude land surface modeling. [ABSTRACT FROM AUTHOR]

The transport processes of methane (CH4) in tree stems remain largely unknown, although they are critical in assessing the whole‐forest CH4 dynamics. We used a physically based dynamic model to study the spatial and diurnal dynamics of stem CH4 transport and fluxes. We parameterised the model using data from laboratory experiments with Pinus sylvestris and Betula pendula and compared the model to experimental data from a field study. Stem CH4 flux in laboratory and field conditions were explained by the axial advective CH4 transport from soil with xylem sap flow and the radial CH4 diffusion through the stem conditions. Diffusion resistance caused by the bark permeability did not significantly affect gas transport or stem CH4 flux in the laboratory experiments. The role of axial diffusion of CH4 in trees was unresolved and requires further studies. Due to the transit time of CH4 in the stem, the diurnal dynamics of stem CH4 fluxes can deviate markedly from the diurnal dynamics of sap flow. Summary statement: We characterised methane transport processes in boreal trees using a dynamic transport model. Our model explains stem methane fluxes in laboratory and field conditions when sapflow velocity and radial diffusion are considered. The model can be used to decrease uncertainty in global methane budget. [ABSTRACT FROM AUTHOR]

As soil microbial respiration is the major component of land CO2 emissions, differences in the functional dependence of respiration on soil moisture among the Earth system models (ESM) contributes significantly to the uncertainties in their projections. Using soil organic C (SOC) stocks and CO2 data from a boreal forest – mire ecotone in Finland and Bayesian data assimilation, we revised the precipitation-based environmental function of the Yasso07 soil carbon model. We fit this function to the observed microbial respiration response to moisture and compared its performance against the original Yasso07 model and the version used in the JSBACH land surface model with a reduction constant for decomposition rates in wetlands. The Yasso07 soil C model coupled with the calibrated unimodal moisture function with an optimum in dry soils accurately reconstructed observed SOC stocks and soil CO2 emissions and clearly outperformed previous model versions on paludified organo-mineral soils in forested peatlands and water-saturated organic soils in mires. The best estimate of the posterior moisture response of decomposition used both measurements of SOC stocks and CO2 data from the full range of moisture conditions (from dry/xeric to wet/water-saturated soils). We observed unbiased residuals of SOC and CO2 data modelled with the moisture optimum in well-drained soils, suggesting that this modified function accounts more precisely for the long-term SOC change dependency according to ecosystem properties as well as the contribution of short term CO2 responses including extreme events. The optimum moisture for decomposition in boreal forests was in dry well-drained soils instead of the mid-range between dry and water-saturated conditions as is commonly assumed among many soil C and ESM models. Although the unimodal moisture modifier with an optimum in well-drained soils implicitly incorporates robust biogeochemical mechanisms of SOC accumulation and CO2 emissions, it needs further evaluation with large scale data to determine if its use in land surface models will decrease the uncertainty of projections. [ABSTRACT FROM AUTHOR]

In the future management and sustainable use of boreal forests, it is crucial to consider the rate and strength of tree responses to an elevated water table and the concurrent oxygen limitations, especially in peatlands. We examined the response dynamics of 7-year-old Scots pine (Pinus sylvestris L.) seedlings to a 5-week waterlogging (WL) treatment during a growing season in a root lab (dasotron) experiment. WL took place after shoot elongation had ended but while growth of the trunk diameter was still in progress. Trunk sap flow and needle water potential started to decrease immediately after the onset of WL, while the first signs in needle gas exchange--seen as decreases in the potential efficiency of photosystem II, the rates of light-saturated net assimilation and transpiration, and increased needle respiration--were observed after 3 weeks of WL. New needles responded to WL more strongly than the old ones. Drainage with consequent re-oxygenation of the soil caused a further decrease in sap flow. We conclude that through negative feedback on transpiration and net photosynthesis, WL during the growing season is harmful for Scots pine, leading to potential growth losses or even dying of trees within a few weeks of WL. Key words: hypoxia, hydrology, peatland forestry, photosynthesis, sap flow. Pour l'amenagement futur et l'utilisation durable des forets boreales, il est essentiel de tenir compte du taux et de la robustesse de la reaction des arbres a l'elevation de la nappe phreatique et a l'appauvrissement simultane en oxygene, particulierement dans les tourbieres. Nous avons etudie la dynamique des reactions de semis de pin sylvestre (Pinus sylvestris L.) ages de 7 ans a un engorgement du sol d'une duree de 5 semaines au cours d'une saison de croissance lors d'une experience dans un laboratoire racinaire (dasotron). L'engorgement du sol est survenu apres que l'elongation des pousses eut ete completee mais pendant que la croissance en diametre du tronc etait toujours en cours. Le flux de seve dans le tronc et le potentiel hydrique des aiguilles ont commence a diminuer immediatement apres le debut de l'engorgement du sol, tandis que les premiers signes dans les echanges gazeux foliaires, visibles par la diminution de l'efficacite potentielle du photosysteme II, les taux de transpiration et d'assimilation nette a saturation lumineuse, ainsi que par l'augmentation de la respiration des aiguilles, ont ete observes apres 3 semaines d'engorgement du sol. Les nouvelles aiguilles ont reagi plus fortement a l'engorgement du sol que les vieilles aiguilles. Le drainage suivi de la reoxygenation du sol a cause une nouvelle diminution du flux de seve. Nous concluons que par l'intermediaire d'une retroaction negative sur la transpiration et la photosynthese nette, l'engorgement su sol durant la saison de croissance est nefaste pour le pin sylvestre et entraine des pertes potentielles de croissance ou meme la mort des arbres apres quelques semaines. [Traduit par la Redaction] Mots-cles: hypoxie, hydrologie, foresterie des tourbieres, photosynthese, flux de seve., Introduction Excess water, with consequently declined soil aeration, is one of the limiting factors in tree growth in the boreal zone, especially in the peatlands that extend to about 10% [...]