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High resolution thermal infrared (TIR) imaging is opening up new vistas in biosphere-atmosphere heat exchange studies. The rapidly developing unmanned aerial systems (UAS) and specially designed TIR cameras offer opportunities for TIR survey with increasingly high resolution, reduced noise, prolonged flight times and better gimbals. A state-of-the-art science platform is assembled using a Matrice 210 V2 drone equipped with a Zenmuse XT2 thermal camera and deployed over a pristine boreal peatland with the aim to test its performance in a heterogeneous ecosystem with short vegetation. The study utilizes the capability of the UAS platform to hover for prolonged times (about 20 min) whilst recording high-frequency (1-30 Hz) TIR videos. A methodology to derive thermal signatures of near-ground coherent turbulent structures impinging on the land surface, surface temperature spectra and heat fluxes from the retrieved videos is developed. The size, residence time and movement of the coherent structures are computed from the surface temperature maps, and their dependency on atmospheric conditions is examined. A ground-based eddy-covariance system and a collocated meteorological setup are used for reference. [ABSTRACT FROM AUTHOR]

In the hydrological cycle, water is lost from terrestrial ecosystems either laterally through stream runoff or vertically as evapotranspiration (ET) back to the atmosphere. Although it is well known that ET losses represents an important water loss pathway at local to global scales, the magnitude and relative importance of ET and its individual flux components varies considerable among different ecosystems. In this study, we combined empirical sapflux and eddy covariance measurements with estimates from a process-based model to partition the water balance in a boreal forested catchment. This study was conducted within the Krycklan Catchment, which has state-of-the-art infrastructure for hydrological measurements, thereby providing us the unique opportunity to compare the absolute and relative magnitude of ET and its flux components to other water loss pathways (i.e., stream runoff). During the growing season, ET was the major water loss pathway, representing ca. 85% of the incoming precipitation and being roughly 7 times greater than stream runoff. Both the empirical results and model estimates suggested that tree transpiration (T) and canopy interception (IL) represented 45% and 35% of total ET loss; respectively, and thus together were responsible for 70% of the water loss during the growing season. Understory evapotranspiration (ETu) was less important than T and IL during most of the study period, except for late autumn when ETu was the largest ET flux component. Overall, our study highlights the importance of trees in regulating the water cycle of boreal catchments, implying that forest management impacts on stand structure as well as climate change effects on tree growth are likely to have large cascading effects on the way water moves through these forested landscapes. [ABSTRACT FROM AUTHOR]

We can curb climate change by improved management decisions for the most important terrestrial carbon pool, soil organic carbon stock (SOC). However, we need to be confident we can obtain the correct representation of the simultanous effect of the input of plant litter, soil temperature and water (which could be altered by climate or management) on the decomposition of soil organic matter. In this research, we used regression and Bayesian statistics for testing process‐based models (Yasso07, Yasso15 and CENTURY) with soil heterotrophic respiration (Rh) and SOC, measured at four sites in Finland during 2015 and 2016. We extracted climate modifiers for calibration with Rh. The Rh values of Yasso07, Yasso15 and CENTURY models estimated with default parameterization correlated with measured monthly heterotrophic respiration. Despite a significant correlation, models on average underestimated measured soil respiration by 43%. After the Bayesian calibration, the fitted climate modifier of the Yasso07 model outperformed the Yasso15 and CENTURY models. The Yasso07 model had smaller residual mean square errors and temperature and water functions with fewer, thus more efficient, parameters than the other models. After calibration, there was a small overestimate of Rh by the models that used monotonic moisture functions and a small generic underestimate in autumn. The mismatch between measured and modelled Rh indicates that the Yasso and CENTURY models should be improved by adjusting climate modifiers of decomposition or by accounting for missing controls in, for example, microbial growth. Highlights: We tested soil carbon models against monthly soil Rh fluxes and amounts of SOC stock.The models accurately reproduced most of the seasonal Rh trends and amounts of SOC.Under autumn temperature and moisture, Rh was mismatched before and even after the parameterization.The seasonality of the temperature and water functions should be adjusted in models. [ABSTRACT FROM AUTHOR]

Vegetation is known to have strong influence on evapotranspiration (ET), a major component of terrestrial water balance. Yet hydrological models often describe ET by methods unable to sufficiently include the variability of vegetation characteristics in their predictions. To take advantage of increasing availability of high-resolution open GIS-data on land use, vegetation and soil characteristics in the boreal zone, a modular, spatially distributed model for upscaling ET and other hydrological processes from a grid cell to a catchment level is presented and validated. An improved approach to upscale stomatal conductance to canopy scale using information on plant type (conifer / deciduous) and stand leaf-area index (LAI) is proposed by coupling a common leaf-scale stomatal conductance model with a simple canopy radiation transfer scheme. Further, a generic parametrization for vegetation and snow-related hydrological processes for Nordic boreal forests is derived based on literature and data from a boreal FluxNet site. With the generic parametrization, the model was shown to well reproduce daily ET measured by eddy-covariance technique at ten conifer-dominated Nordic forests whose LAI ranged from 0.2 to 6.8 m² m-2. Topography, soil and vegetation properties at 21 small boreal headwater catchments in Finland were derived from open GIS-data at 16 x 16 m grid size to upscale water balance from a stand to catchment level. The predictions of annual ET and specific discharge were successful in all catchments, located from 60 to 68°N, and daily discharge also reasonably well predicted by calibrating only one parameter against discharge data measurements. The role of vegetation heterogeneity on soil moisture and partitioning of ET was demonstrated. The proposed approach can support e.g. in forest trafficability forecasting and predicting the impacts of climate change and forest management on stand and catchment water balance. With appropriate parametrization it can be generalized outside the boreal coniferous forests. [ABSTRACT FROM AUTHOR]

Photosynthesis provides carbon for the synthesis of macromolecules to construct cells during growth. This fact generates the key role of photosynthesis in the carbon dynamics of ecosystems (Taiz et al., 2015) and biogenic CO2 consumption. The development of eddy covariance measurements of ecosystem CO2 fluxes started a new era in the field studies of photosynthesis (Baldocchi et al., 2000). However, the interpretation of the very variable CO2 fluxes in evergreen forests has been problematic especially in transition times such as the spring and autumn. We apply two theoretical needle-level equations that connect the variation in the light intensity, stomatal action and the annual metabolic cycle with photosynthesis. We then show that these equations are able to predict quite precisely and accurately the photosynthetic CO2 flux between the atmosphere and different ecosystems in five Scots pine stands located from northern timberline to Central Europe. Our result has strong implications on the interpretation of the effects of the global change on the processes in boreal forests, especially of the changes in the metabolic annual cycle of photosynthesis. [ABSTRACT FROM AUTHOR]

Ditch network maintenance (DNM) is implemented on 60 000 ha annually in Finland to sustain timber productivity on drained peatlands.We investigated how different DNM strategies influence the total ditching area, timber production, financial feasibility, and sediment and nutrient loading in the South-West Finland (SWF) and Northern Ostrobothnia (NO) regions. The National Forest Inventory sample plot data were entered into a stand simulator and simulations were carried out over a 100-year period. In the Passive DNM strategy (ditches maintained only at forest regeneration), the total ditching area was 72-85% lower compared with the Intensive strategy (DNM always when ditches are in poor condition) or 62-80% lower compared with the Conditional strategy (DNM only when ditches are poor and standing volume is below a specific value). Conditional and Intensive strategies resulted in higher cutting removals than the Passive strategy (8-9% in SWF and 21-22% in NO) due to faster stand development, but the respective loads of suspended solids (SS) and phosphorus were two- to three-fold higher in SWF and four- to six-fold higher loads in NO. Overall, the Conditional strategy showed the best performance generating the highest net present value, higher cutting removals than in the Passive strategy, and lower nutrient and SS loads than in the Intensive strategy. [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. [ABSTRACT FROM AUTHOR]

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Canopy structure is one of the most important vegetation characteristics for land-atmosphere interactions, as it determines the energy and scalar exchanges between the land surface and the overlying air mass. In this study we evaluated the performance of a newly developed multilayer energy budget in the ORCHIDEE-CAN v1.0 land surface model (Organising Carbon and Hydrology In Dynamic Ecosystems - CANopy), which simulates canopy structure and can be coupled to an atmospheric model using an implicit coupling procedure. We aim to provide a set of acceptable parameter values for a range of forest types. Top-canopy and sub-canopy flux observations from eight sites were collected in order to conduct this evaluation. The sites crossed climate zones from temperate to boreal and the vegetation types included deciduous, evergreen broad-leaved and evergreen needle-leaved forest with a maximum leaf area index (LAI; all-sided) ranging from 3.5 to 7.0. The parametrization approach proposed in this study was based on three selected physical processes - namely the diffusion, advection, and turbulent mixing within the canopy. Short-term sub-canopy observations and long-term surface fluxes were used to calibrate the parameters in the sub-canopy radiation, turbulence, and resistance modules with an automatic tuning process. The multi-layer model was found to capture the dynamics of sub-canopy turbulence, temperature, and energy fluxes. The performance of the new multi-layer model was further compared against the existing single-layer model. Although the multi-layer model simulation results showed few or no improvements to both the nighttime energy balance and energy partitioning during winter compared with a single-layer model simulation, the increased model complexity does provide a more detailed description of the canopy micrometeorology of various forest types. The multi-layer model links to potential future environmental and ecological studies such as the assessment of in-canopy species vulnerability to climate change, the climate effects of disturbance intensities and frequencies, and the consequences of biogenic volatile organic compound (BVOC) emissions from the terrestrial ecosystem. [ABSTRACT FROM AUTHOR]

Canopy structure is one of the most important vegetation characteristics for land-atmosphere interactions, as it determines the energy and scalar exchanges between the land surface and the overlying air mass. In this study we evaluated the performance of a newly developed multi-layer energy budget in the land surface model ORCHIDEE-CAN (Organising Carbon and Hydrology In Dynamic Ecosystems - CANopy), which simulates canopy structure and can be coupled to an atmospheric model using an implicit coupling procedure. We aim to provide a set of acceptable parameter values for a range of forest types. Top-canopy and sub-canopy flux observations from eight sites were collected in order to conduct this evaluation. The sites crossed climate zones from temperate to boreal and the vegetation types included deciduous, evergreen broad leaved and evergreen needle leaved forest with a maximum LAI (all-sided) ranging from 3.5 to 7.0. The parametrization approach proposed in this study was based on three selected physical processes - namely the diffusion, advection and turbulent mixing within the canopy. Short-term sub-canopy observations and long-term surface fluxes were used to calibrate the parameters in the sub-canopy radiation, turbulence and resistances modules with an automatic tuning process. The multi-layer model was found to capture the dynamics of sub-canopy turbulence, temperature and energy fluxes. The performance of the new multi-layer model was further compared against the existing single-layer model. Although, the multi-layer model simulation results showed little or no improvements to both the nighttime energy balance and energy partitioning during winter compared with a single-layer model simulation, the increased model complexity does provide a more detailed description of the canopy micrometeorology of various forest types. The multi-layer model links to potential future environmental and ecological studies such as the assessment of in-canopy species vulnerability to climate change, the climate effects of disturbance intensities and frequencies, and the consequences of biogenic volatile organic compounds (BVOC) emissions from the terrestrial ecosystem. [ABSTRACT FROM AUTHOR]