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Understanding how forest ecosystems respond to environmental factors, particularly in the context of global climate change, is essential for devising effective mitigation strategies. This study focuses on quantifying the interaction between forest ecosystems and atmospheric gases. To achieve our objectives, we are using the eddy covariance (EC) flux method to measure air turbulence and gas concentrations above the forest canopy at the Station for Measuring Ecosystem-Atmosphere Relations (SMEAR) in southern Estonia. We apply a flux footprint (FFP) model to describe the spatial extent and position of the surface area contributing to the turbulent flux measurements. The FFP analysis provides valuable insights into the long-term changes in SMEAR Estonia, the FFP and its relationship with forest management and land use changes. Our findings reveal that the FFP area varies from year to year due to changes in wind speed and direction, affecting the contribution of different land cover elements to the overall FFP. The average changes in the FFP area at a height of 30 meters were approximately 4.9%, while those at a height of 70 meters were only 1.6%. Moreover, human activities, such as thinning and clear-cutting, influence the growing stock and increment of forest stands.

In this study, assortment yields were studied for Scots pine, Norway spruce, birch spp. (silver and downy birch), European aspen, black alder, and grey alder stand elements. Theoretical assortment yields were calculated using the Ozolinš’ stem taper curve, incorporating tree diameters and heights. The modelled results were compared with actual yields provided by the State Forest Management Centre. During the study, differences in timber assortments and firewood yields were modelled compared to actual data. Changes in wood assortment yields, compared with undamaged and straight trees, depended on the tree species, stand site index, and stand element age. For Scots pine, depending on the stand site index and age, the reduction in log volume ranged from 7 to 28% of the total volume of all assortments. For Norway spruce, it was 5–30%, for birch spp. 30–70%, for aspen 50–90%, for black alder 20–50% and grey alder 5–30%. The increase in firewood volume according to the volume of all assortments was 3–4% for Scots pine, 5–14% for Norway spruce and birch spp., and 5–16% for European aspen. The difference between log and firewood changes represents the change in pulpwood. Over time, the need for new studies arises to adapt to evolving industry practices, including changes in log diameters and quality criteria. The appendix outlines steps that programmers can take to utilize the developed model.

The stand level gross volume increment models are used to estimate the future production of tree stands. Very often, the stand growth and yield in the models used in practice are described by the tree volume increment that includes the diameter growth function with the tree height together with stem taper as the input variables. The currently used function of stand volume increment in Estonia included also stand relative density as an additional input variable. In the current study, we developed a basal area increment function based on the periodic measurement data of the Estonian Network of Forest Research Plots (ENFRP). As in the earlier model of stand volume increment developed by Priit Kohava, in the current model the basal area increment of tree species is developed for a pure stand, and for mixed stands, the proportion of the tree species’ basal area is used. The tests in our data indicated that the periodic increment prognosis had good fit in the case of variable share of tree species in the main storey and coincide with the earlier studies by Finnish and Swedish colleagues. The developed model of basal area increment predictions are expectedly higher than the earlier model predictions for the most tree species and stand relative densities.

Wood moisture content (MC) has a significant impact on all electrical properties of wood. Regarding the development of the (so-called polarization-type) wood moisture meter with the electrical charging effect for monitoring and controlling the wood drying process, it is of interest to expand the theoretical background of this type of novel wood moisture meter by means of modelling. Two mediums were selected for modelling – raw birch wood and, as a reference medium, birch liquid sap – into which two symmetrical carbon fibre measuring electrodes were inserted. In both mediums, direct current and alternating current were passed between electrodes at different electrode potentials. The electrical field and electrical response of the current-affected mediums were then measured and modelled in the time domain and frequency domain. The numerical results of modelling are comparable both in the time domain and frequency domain (i.e. if E = 1.8V, then Cs = 0.5 mF and C1,int = 0.7 mF). The concept of energetic chargeability (CHA(W)) of wood was defined and compared to conventional chargeability as defined by C. Schlumberger in 1913. Empirical dependencies of CHA(W) on electrode potential and primary energy W1 transmitted through the wood (sap) medium were found. In the frequency domain, frequency dependencies were found to distinguish between adsorption processes and mixed kinetics ranges in birch sap and in raw birch wood.

The study area is in the Järvselja Training and Experimental Forest Centre, Estonia. The conservation of Järvselja old-growth forest started in 1924 when the area was excluded from all management activities and left to natural development. The aim of this study is to analyse the methods for calculating single tree height, tree stem lateral surface area, tree volume and carbon content for standing live trees, standing dead trees and for downed deadwood in old-growth forests. The study used the data of 6205 live trees, 1119 snags, 270 standing dead trees and 2983 deadwood trunks from the measured area. The most abundant tree species in Järvselja old-growth forest were Norway spruce and linden. During the last hundred years, the number of dominating tree species has increased slightly. The standing volume of birch, common aspen and Scots pine have been declining while for linden and black alder it has been increasing. In the comparison of tree height curves, the best results were obtained with the Näslund function, however, the Chapman-Richards function with fitting showed slightly better results for two tree species.

The study material of Scots pine sample trees originated from five different forest site types (Cladonia, Calluna, Myrtillus, natural raised bog and drained raised bog) in Estonia. Altogether, 60 trees were sampled from 10 stands. From these, test disks and sample blocks (1.2 m in length) were cut at 1.3 m height, 1/2 of tree height and 3/4 of tree height. We analysed the effect of forest site type on the growth of tree ring width, proportion of late- and heartwood, oven-dry density, bending and compression strength and wood hardness. Wood properties in stands of the same age showed great variability. Significant differences were found in the wood properties between site types. Wood density and strength characteristics were higher in samples from heath site types than from the sites more optimal for pine (e.g., Myrtillus). The quality of the wood from peatland stands was lower than from trees grown on mineral soil. The decreasing trend in strength properties towards the top of trees was steeper in the wood formed under poor nutrient conditions. Latewood proportion increased with tree age. However, in the case of equal latewood percentages, heartwood density was higher than sapwood density.

Estimations of forests’ carbon sequestration capacity relies on proper assessment of the eddy covariance measurement mast’s footprint. Harsh winter temperatures in Estonia lead to ice formation on 3D sonic anemometer sensor heads and thus induce measurement gaps in the data. To maximise data availability, we use a smart heating algorithm to minimise ice formation on the anemometer sensor heads. Here, we studied the temperature distribution of ice formation on the measurement instruments. Three major temperature ranges were found, between 0°C and −3°C, which is the most abundant temperature range for ice formation, and two temperature regions with peaks around −10°C and −20°C. Our algorithm to prevent ice formation led to very short median heating intervals of about 25 to 30 seconds.

Three cases of violation of forest management regulations in Estonia in 2004, 2005 and 2007 are presented in the study where the required lower limit of basal area after thinnings was not followed. These stands were revisited in 2017 to assess the impacts of such thinnings. The actual thinnings were well justified from the silvicultural and economic viewpoints. All three stands were ecologically in good condition in 2017. Also, all three stands had already reached the required age or dimensions allowing regeneration cutting in 2017. Forest management regulations on thinning did not work well in the studied cases and therefore some changes in the current regulations are necessary in Estonia.

The properties of biomass-based fuel and combustion tests showed that logging residues are promising renewable energy sources. The data used in this study were collected from four clear-felling areas in Järvselja Training and Experimental Forest Centre, Southeast Estonia in 2013–2014. Logging was carried out by harvesters in Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies [L.] Karst.), silver birch (Betula pendula Roth.) and black alder (Alnus glutinosa L. Gaertn.) dominated stands with a small admixture of other tree species according to the cut-to-length method and logging residues were placed in heaps. The aim of this research is to assess different characteristics of logging residues (quantity, moisture content, energetic potential, ash content and amount) in clear-felling areas. The highest load of slash was measured on the birch dominated study site, where the dry weight of the logging residues was 29 t ha−1. Only the branch fraction moisture content on the black alder dominated site (35.4%) was clearly different from respective values on other sites (21.6–25.4%). The highest calorific value of the residues was assessed with the residues from the birch dominated site, where in moist sample it was 365 GJ ha−1 and in dry matter 585 GJ ha−1. The heating value of the fresh residues is highest in coniferous trees. The highest ash content in branch segments was registered for the black alder dominated site. Järvselja data indicate higher quality in conifer dominated sites, yet a higher load of logging residues in broadleaf dominated stands.

The breeding of forest tree species in the Baltic region has notably contributed to wood production for the bioeconomy. Growth modelling is used for long-term estimates of forest development. However, usually based on data from unimproved stands, they may underestimate the growth of improved trees. Accordingly, it is important to identify and integrate the altered stand dynamics associated with improved planting stock into existing growth models to accurately capture the resulting gains or, alternatively, develop new functions specifically designed for improved trees. We used the generalized algebraic difference approach to model and analyze height growth patterns of Scots pine and silver birch with different genetic improvement levels (improved forest reproductive material categories 'qualified' and 'tested'). Modelling was based on 14 260 and 55 926 height–age series from open-pollinated progeny trials in Latvia and Lithuania with an age range of 3–46 and 5–22 years for pine and birch, respectively. Dynamic generalized algebraic difference approach forms of commonly applied height growth functions with forest reproductive material-category-specific sets of coefficients were tested. The dynamic form of the Chapman–Richards and King–Prodan equations had the best fit for Scots pine and silver birch, respectively. The expected height growth of the category 'tested' was slightly better than the one for 'qualified', with more distinct differences in silver birch. The model with forest reproductive material-category-specific coefficients reflected the actual growth of improved trees; however, such application is limited to sites with medium and high site indices, where improved planting stock is typically used. We recommend the model for young stands up to the age of 20 and 40 years for pine and birch, respectively, considering the empirical data cover on which the functions are based. A unified dynamic height model with the same functional form but category-specific parameterization for different improvement levels allows a practical applicability and effective communication amongst diverse users, thereby promoting the utilization of the model amongst forest owners and managers who possess information regarding the origin of planting stock. [ABSTRACT FROM AUTHOR]

With the rapid development in data acquisition and presentation, there is a growing interest in virtual forests and computer visualization tools. Forest owners have become more aware about their property and are interested in applying different forest management methods and silvicultural techniques. The tools are also applicable in assessment of the changes to the landscape as a result of natural and anthropogenic disturbances. Virtual reality offers a good opportunity to test and compare different management options before implementing decisions which can lead to irreversible consequences. Advances in spatial and temporal data collection enable new and practical solutions for analysis and visualization of long-term natural processes with new forestry applications. In the near future, forest owners and managers will have the possibility to make management decisions without the direct need to exit the office. Furthermore, the learning process is more enthralling and also more profound through augmented reality, helping to foster better working practices even before starting a job in the forest sector.

Diverse structural elements play an important role in sustaining biodiversity in old-growth forests. Therefore, it is important to have thorough knowledge about these habitats and their condition in protected areas. Metsakorralduse Büroo OÜ conducted a large-scale Natura 2000 forest habitat inventory that covered 60% of Lahemaa National Park (LNP) area. Western taiga habitat data (7,191 ha) from this inventory was used for analysis of forest stages. The data was grouped according to stand classes by total area and these classes were compared by deadwood occurrence and relative density. For more precise evaluation of coarse woody debris (CWD) we used 27 sample plots from the Estonian Network of Forest Research Plots (ENFRP) located in LNP. The biggest areas of Western taiga habitat were covered by mature and old stages. CWD occurrence (over 5 m3ha−1 of snags and logs) by habitat representativeness is higher in old and natural forest classes. This logical result is overshadowed by the outcome that the CWD was not substantially present on 32% of the area in the old-growth forest class. This indicates that these areas lack the potential of biological legacies to provide critical niche habitats for different species. The study shows that the CWD quantity in Estonian conditions is similar to that reported in previous studies in this region, but because many of the older forest stage classes do not have any CWD present, these areas should include ecological restoration practices in their conservation planning. By creating snags, logs and gaps in these areas, we are able to create better structural variability and include wood into different decay processes.

A new paradigm in forest management using a streaming input of public participation needs effective online solutions. The process should be real-time, secure, effective and efficient. People are expected to share their data and thoughts on forest management with forest owners for improving forest management and planning. The participatory approach supports communication within society and can be designed as an interactive web-based solution. Many pre-requisites have already been met and society is ready for a successful start of an interactive participatory forest planning system in Estonia. People use digital identification for various purposes and the state already maintains an online public forest register. Motivating people to participate in the planning process is always challenging yet important for the successful implementation of the system. The system should allow simulating the development and management of forest stands following the participatory input and using ecosystem models and economic calculations. The outputs from the system include management alternatives, risk assessments and financial reports. The system requires a reliable financial compensation scheme to ensure overall long-term stability of the system and agreements between interested persons or groups and forest owners.

Establishment of the SMEAR Estonia at a hemiboreal mixed deciduous broad-leaved-evergreen needle-leaved forest at Järvselja, South-Eastern Estonia, has strongly enhanced the possibilities for national and international cooperation in the fields of forest ecosystem – atmosphere research and impacts of climatic changes on forest ecosystems, atmospheric trace gases, aerosols and air ions. The station provides a multitude of comprehensive continuously measured data covering key climatic and atmospheric characteristics (state and dynamics of solar radiation, trace gases, aerosols and air ions, meteorological parameters) and forest ecosystem traits (net primary productivity, individual tree growth, gas-exchange characteristics, soil variables). The station follows a multidisciplinary and multiscale approach covering processes in spatial dimensions ranging from nanometres to several hundred square kilometres, being thus able to significantly contribute to worldwide measurement networks and the SMEAR network. Here we present an overview of the station, its data produced and we envision future developments towards sustainable research and development of the large-scale scientific infrastructure SMEAR Estonia.

Growth assessment of young stands gives the possibility of assessing forest site potential, tree species-dependent competition and developing realistic predictions for the following periods. The study is conducted in naturally regenerated broadleaves dominated stands in 2005 at Järvselja Training and Experimental Forest Center. The current study material is collected from 9 study plots established in three forest stands (regeneration felling years respectively 1996, 2000 and 2002). The study plots were re-measured 4–6 times respectively between the years of 2006 and 2012. The Weibull distribution function fit for empirical height distributions in consecutive years was tested and the estimated Weibull parameters were analysed. Results indicate that empirical height distributions of young regenerated forests do not fit well to theoretical distributions, but in many cases, empirical and theoretical distribution are similar. The Weibull distribution shape parameter was related to the maximum height and range of the height, and the scale parameter was related to the mean, quadratic mean and median height.

Changes in the society have created a need for a systematic approach in forestry combining forest management, timber harvest analysis, research and demonstration of new technologies. A research and demonstration area is an option for explaining and visualising frameworks of forest design, modelling and planning in the real nature. A research and demonstration area of forest management planning can be defined as a forested landscape that combines various forest uses and aims to ensure and explain forest management strategies as well as conservation of ecosystems and natural resources. A suitable area for creating the research and demonstration area of forest management planning is at Järvselja Training and Experimental Forest Centre in Estonia. It has naturally diverse forests and these include also habitats of several rare and endangered species and already comprise different sets of nature conservation areas. The centre has been used for forestry higher education and research for over 90 years and therefore all essential infrastructure has been developed including dormitories and lecture rooms for field training as well as different nature paths, old field experiments (e.g. initial spacing and thinning experiments) and new modern research facilities. Forest management plans and inventory data since 1922 still exist for the area. The area at Järvselja is expected to demonstrate present studies and research work in the most comprehensive way as well as the implications to forest management and the newest technologies in forest management and planning. Different systems and techniques of forest management can be studied and demonstrated to the wider public by establishing the research and demonstration area of forest management planning at Järvselja.

Forest research has long traditions in Estonia that can be traced back to the 19th century. Data from long-term forest experiments are available since 1921. The first studies mainly focused on silvicultural treatments and application of such data for understanding and modeling ecological processes was limited. The Department of Forest Management of the Estonian University of Life Sciences started to develop the Estonian Network of Forest Research Plots (ENFRP) in 1995. Since then, plots have been continuously re-measured with 5-year interval. Approximately 100-150 permanent sample plots were measured annually. In 2014, the long-term research network consisted of 729 permanent sample plots, of which 699 have been re-measured at least once, 667 plots - twice and 367 plots - three times. The total number of trees recorded in the network database amounts to 130,479. The plots are systematically distributed throughout the country. Detailed dendrometric measurements including tree spatial distribution are part of the survey protocol. Initially the network was set up to produce suitable data for development of individual tree growth models for Estonia. The significance of the network for the Estonian forest research is continuously increasing and nowadays ENFRP is recognized as an important national research infrastructure.

We present the change in the thermal growing season based on a unique long-term climatological data set obtained at the Järvselja Training and Experimental Forestry Centre in southeast Estonia. The data cover the years 1955-2020 and we employed the growing degree-days (GDD) algorithm on them. We defined the days when temperature is persistently above 5°C as GDD5; when above 10°C as GDD10. Our results showed that both GDD5 and GDD10 have increased by 14.8 (2.2 days/decade) and 18 (2.8 days/decade) days, respectively. The recent average growing season length is 204 days in case of GDD5 and 164 days in case of GDD10. Our results reveal that during the most recent decade, the length is stagnating and the onset in spring delays while the growing season's end extends towards winter. We find that the number of extreme cold (below -20°C) dropped by a factor of 3.3 while extreme warm days (above +25°C) rose by a factor of 2.6. Possible implications of these changes on the forest ecosystem are discussed. [ABSTRACT FROM AUTHOR]