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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.

Knowledge about the seasonal dynamics of tree growth and its relationship with environmental factors is necessary to eliminate the uncertainty due to ongoing climate change and for more precise growth modelling when re-measurements are done periodically. Despite the increasing number of studies monitoring seasonal wood formation, a considerable part of European forests, including Estonia, lacks such information. In this article, we present a date-dependent model for determining the share of seasonal radial growth for the three most common tree species in the region (Scots pine, Norway spruce and silver birch) for Estonian conditions. Since seasonal tree growth monitoring data were unavailable for Estonia, we used published seasonal radial growth data from Lithuania by Dr Adomas Vitas (2011). We tested four functions (Kumaraswamy, Weibull, Gompertz and logistic) on obtained data to approximate the seasonal development of radial growth. Kumaraswamy’s function could track the course of seasonal radial growth gains the best; thus, this function was chosen for further use. We obtained data on intra-annual radial growth from published research studies from neighbouring countries and determined the dates of growth initiation and cessation for Estonian conditions. Finally, we combined Kumaraswamy’s function and the predicted radial growth onset and cessation dates into the model that could predict the seasonal growth course and thus were able to estimate the share of newly formed increment from the dates.

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.

2007. aastal rajati Järvseljal kolm ühe hektari suurust katseala, kui kaardistati ja mõõdeti üle kõik puud simulatsioon eksperimentide korraldamiseks (Kuusk, et al., 2013; Widlowski et al., 2015). Need kolm puistut (vt fotod lisas 1) esindavad tüüpilist liitunud võrastikuga kuusikut, kaasikut ja siirdesoo männikut. Kaasikus oli tehtud 2004. aastal harvendusraie, 2018. aastal puhastati katseala alusmetsast, et valmistada ala ette maapealse laser skanneriga mõõtmisteks. Kuusikus ja männikus teadaolevalt viimase 30 aasta jooksul raieid tehtud ei ole. Katsealade (joonised 1, 3, 5) nurkade koordinaadid on mõõdetud diferentsiaal-GPS meetodiga peale mahamärkimist (tabel 1). 2019. aasta kordus mõõtmiste tulemusena ilmnes, et puistute rinnaspindala, keskmine kõrgus ning keskmise puu rinnasläbimõõt olid kasvanud (tabelid 2–4). Puude arv oli kahanenud kõigis puistutes, välja arvatud kaasikus, kus 2018. aasta puhastus raie käigus jäeti alles selleks ajaks 4 cm rinnasdiameetri saavutanud puud. Kuusikus saadi tulemuseks, et võrade raadiused olid võrreldes 2007. aastaga kahanenud. Kas tegemist on võra projektsiooni välispiiri erineva tõlgendamise või tegelikult toimunud muutusega, võiks edaspidi selguda 2013. (Kuusk et al., 2015) ja 2019. aastal tehtud maapealse laserskanneri mõõtmiste andmete analüüsist.

Since 1999, Estonia has conducted the National Forest Inventory (NFI) on the basis of sample plots. This paper presents a new module, incorporating remote-sensing feature variables from airborne laser scanning (ALS) and from multispectral satellite images, for the construction of maps of forest height, standing-wood volume, and tree species composition for the entire country. The models for sparse ALS point clouds yield coefficients of determination of 89.5–94.8% for stand height and 84.2–91.7% for wood volume. For the tree species prediction, the models yield Cohen's kappa values (taking 95% confidence intervals) of 0.69–0.72 upon comparing model results against a previous map, and values of 0.51–0.54 upon comparing model results against NFI sample plots. This paper additionally examines the influence of foliage phenology on the predictions and discusses options for further enhancement of the system.

The availability of a large amount of data from reliable sources is important for forest growth modelling. A permanent plot where trees are repeatedly measured provides a clearer picture of stand alterations. Various factors, including forest management, affect forest growth and accuracy of its assessment. In Estonia, mean height as a regression height prediction at mean square diameter is commonly used in forest management practice. Alternatively, dominant height can be used. The main advantage of using dominant height instead of mean height is that the growth of dominant trees is not so strongly affected by stand density (thinning). The aim of our research was to investigate the difference between mean height and dominant height when used as stand height. The research was based on the Estonian Network of Forest Research Plots (ENFRP). As a result, we found that the average mean height change was significantly greater in the case of thinning when compared to undisturbed stand development, whereas, the average dominant height change in the case of thinning compared to undisturbed development was less significant. As a side result, we developed a regression model that can be used for calculating the dominant height of the main tree species using stand attributes (mean height, quadratic mean diameter and density) with a residual standard deviation of 0.466 m.

Forest height increment rate is related to the forest growth conditions. Data bases of previous forest inventories contain information about forest heightage relationship on large number of forest stands while repeated measurements of permanent sample plots provide an excellent reference for comparison. Repeated airborne laser scanning of forest stands is an additional source for the estimation of change in forest structure. In this study, height growth of middle-aged and older forest stands for about 10 year period was compared to an algebraic difference model on permanent sample plots (66) and for a sample of forest stands with repeated airborne laser scanning data (61). The model was based on a large dataset of forest inventory records from the period of 1984–1993. Statistically significant increased forest height growth was found in permanent sample plots based on tree height measurements (9 cm yr−1) as well in stands with repeated laser scanning data (4.5 cm yr−1) in South-East Estonia compared to the algebraic difference model. The difference between the two data sets was explained by their mean age and site class, but the increased forest height growth compared to the old forest inventory data indicates improved growth conditions of forests in the test area. The results hint also that empirical data-based forest growth models need to be updated to avoid biased growth estimates.

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.

A generic regression model for above-ground biomass of forest stands was constructed based on published data (R2 = 0.88, RSE = 32.8 t/ha). The model was used 1) to verify two allometric regression models of trees from Scandinavia applied to repeated measurements of 275 sample plots from database of Estonian Network of Forest Research (FGN) in Estonia, 2) to analyse impact of between-tree competition on biomass, and 3) compare biomass estimates made with different European biomass models applied on standardized forest structures. The model was verified with biomass measurements from hemiboreal and tropical forests. The analysis of two Scandinavian models showed that older allometric regression models may give biased estimates due to changed growth conditions. More biomass can be stored in forest stands where competition between trees is stronger. The tree biomass calculation methods used in different countries have also substantial influence on the estimates at stand-level. A common database of forest biomass measurements from Europe in similar to pan-tropical tree measurement data may be helpful to harmonise carbon accounting methods.

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.

Structural indices and characteristics have often been employed for assessing different aspects of forest stands. In order to assess the performance of such measures in forest sample plots of different size and shape, the current study is based on a data set for a relatively large (1 ha) silver birch dominated stand, and five simulated planar point patterns (a Poisson process, two clustered and two regular patterns) with similar intensity of points distributed on an area equal to the silver birch stand as reference stands. The analyses was based on repeated samplings of the stands, with randomly placed circular or square shaped plots of different sizes, with area ranging from 0.007 to 0.636 ha. Similar centre positions were considered for plots of different shapes, but the locations of the plot centres differed with size, so that plots of different sizes were able to cover the maximum possible area of reference stands. Some structural indices accounting for one or four nearest neighbours, and also the Point-pair correlation function was then quantified for each random sample plot. We used standard deviation and the differences of the mean estimates from the expected values to assess the sensitivity of the structural measures to the size and shape of sampling plots. The results indicated the significant effect of plot size and shape on structural indices. The correlation between plot size and estimates precision was positive, and small plots, regardless of their shapes, showed big variation among them while circular plots often provided more accurate estimates. Even though, as expected, expanding the plots increased the precision of the neighbourhood-based indices’ estimates (spatial measures), and also resulted in inaccurate estimates for some reference stands, depending on the arrangement of trees/points within that stand.

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.

Forest management has become a more complex issue than it has ever been before. Foresters need to fulfill the demands of several interest groups, often which are conflicting. Finding the balance between different management objectives can be facilitated with the use of decision support systems. Since no decision support systems have been developed in Estonia, the aim of this study is to assess the applicability of the Finnish stand growth simulator MOTTI in Estonia. The evaluation focuses on the basal area growth models; the data used originates from the Estonian network of permanent forest growth plots. Tree-level bias models were constructed for all major tree species in order to assess model performance. Also, bias was examined visually with the use of residual plots. Results show that bias levels and variables which contribute to bias differ by species. Based on the fit statistics of the bias models, Common aspen shows the highest bias level whereas the growth of Gray alder seems to be predicted most accurately. Although model performance is decent for a model that is used outside of its application limits, calibration should still be considered as a prerequisite to implement the MOTTI system in Estonian forestry practice.

Altogether 197 grafts were studied in Pauska seed orchard in South-Estonia to find out the effect of the fertilization on Norway spruce grafts. The fertilization trials were carried out in May 1988 and 2006. The grafts of 4 different clones with 5 different fertilization treatments (N, P, K, NPK, control) were under study. The effect of three factors (fertilization, clone and year) on different characteristics of spruce grafts was studied. The linear methods with R software were used to find out relationships between variables. In addition to the morphological features and the content of nutrients in needles, the quantities and qualities of the mean cone and the weight of 1000 seeds were measured. Furthermore, the variation of quantities of needles (density, weight, length) and the content of nutrients in needles between years 1988 and 2007 were compared, using the linear methods with R software package. The morphological characteristics and nutrient content of needles, the mass of cones and seeds have depended the most on a calendar year. During the last research period (2003−2007), the needles of grafts under study were longer, lighter and with lower density compared to earlier research period (1988-1993). The effect of a clone was also essential. Needles of younger grafts were longer, heavier and set sparser than needles of older grafts. The needle nutrient content of younger grafts was also higher compared to the older ones. The effect of fertilizers on the grafts was dependent on the period of time. Nitrogen fertilizers increased the N-content in their needles during the first four years and also after repetitive fertilization. Phosphate fertilizers increased the P-content in their needles starting from the third year after their fertilization. The impact of potassium fertilizers on the K-content of their needles appeared 2−4 years after their fertilization. Combined fertilizers increased the N- and P-content in the needles to some extent, whereas it decreased their Ca- and Mg-content.

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. [ABSTRACT FROM AUTHOR]

Knowledge about the seasonal dynamics of tree growth and its relationship with environmental factors is necessary to eliminate the uncertainty due to ongoing climate change and for more precise growth modelling when re-measurements are done periodically. Despite the increasing number of studies monitoring seasonal wood formation, a considerable part of European forests, including Estonia, lacks such information. In this article, we present a date-dependent model for determining the share of seasonal radial growth for the three most common tree species in the region (Scots pine, Norway spruce and silver birch) for Estonian conditions. Since seasonal tree growth monitoring data were unavailable for Estonia, we used published seasonal radial growth data from Lithuania by Dr Adomas Vitas (2011). We tested four functions (Kumaraswamy, Weibull, Gompertz and logistic) on obtained data to approximate the seasonal development of radial growth. Kumaraswamy's function could track the course of seasonal radial growth gains the best; thus, this function was chosen for further use. We obtained data on intra-annual radial growth from published research studies from neighbouring countries and determined the dates of growth initiation and cessation for Estonian conditions. Finally, we combined Kumaraswamy's function and the predicted radial growth onset and cessation dates into the model that could predict the seasonal growth course and thus were able to estimate the share of newly formed increment from the dates. Knowledge of the seasonal dynamics of tree growth and its relationship with environmental factors is necessary to eliminate climate change's current uncertainty and to model growth accurately. Despite the increasing number of studies on the seasonal growth of trees, such knowledge is lacking in a significant part of Europe, including the Estonian hemiboreal forest. To accurately determine the time between two measurement occasions in the Estonian Network of Forest Research Plots data analysis, it is necessary to consider how much intra-annual growth has been formed at the moment of the re-measurement occasion, because measurement dates usually do not coincide. In this article, we present a model that enables predicting tree seasonal cumulative relative growth at any date for environmental conditions in Estonia. Since seasonal tree growth observations in Estonia are still ongoing, the relative radial growth model developed in this study relies on data of neighbouring countries. We used growth data for Scots pine, Norway spruce and silver birch published by Vitas (2011) which describes relative radial growth over the season. We tested four sigmoid functions (Kumaraswamy (equation 1), Weibull (equation 2), Gompertz (equation 3) and logistic (equation 4)) to model the intra-annual growth dynamics. Guided by the nature of the seasonal growth process of trees, we chose the Kumaraswamy function to estimate the cumulative relative radial growth of trees. For silver birch, this function also had the smallest residual standard error on Vitas' (2011) data, however, for conifers, a statistically better fit was obtained with the Weibull function (Table 2 , Figure 1). For the selected function to correctly determine the course of growth, the beginning (onset) and end of growth are necessary to ascertain, but currently these data are still not available for Estonia. Thus, we used the published research data from neighbouring countries, Lithuania and Finland (Table 1). Since Estonia is located north of Lithuania, the growing season in Estonia probably starts later and ends earlier. There are several studies about Finland where the seasonal growth of trees should start later and end earlier than in Estonia (Jyske et al. , 2014 ; Mäkinen et al., 2008 ; Schmitt et al. , 2004). The data of the beginning (A) and end (B) of the seasonal radial growth of trees collected from the scientific literature (Table 1) were approximated with a linear model (equation 5). The linear model (equation 5) results (Table 3 , Figure 2) revealed that the beginning and end of the seasonal radial growth of the trees depend on the geographical latitude (LAT) and the measurement method (M). The effect of the tree species (PL) factor was not statistically significant in this model. By predicting the onset A and end B of the seasonal radial growth with equation 5 for Estonian conditions (geographic north latitude 58.5 degrees and dendrometer method), we obtained 132.2 and 238.5, respectively, for Scots pine, 132.2 and 234.1 for Norway spruce and 134.6 and 233.7 days for silver birch from the beginning of the year. Using the above estimates, Figure 3 presents the model predictions of the seasonal relative radial growth with the Kumaraswamy function (equation 1 , Table 2) for Estonian conditions. The beginning and end of the growth period varies from year to year (Tarand et al., 2013). Our model is universal, so the user can determine the start and end day of growth according to the weather conditions and geographical location (Western Estonian islands vs South-Eastern Estonia). Further research is needed for this. In order to obtain a more accurate model of intraseasonal growth dynamics and for other tree species in Estonia, it is necessary to carry out long-term, labour-intensive research. [ABSTRACT FROM AUTHOR]

Tree mortality plays a vital role in the accuracy of growth and yield calculations. Economic loss caused by Heterobasidion sp. and Armillaria sp. is a common issue in forestry. Estonian forests, which are mostly managed, are susceptible to fungal infection due to freshly exposed wood surfaces, such as stumps and mechanical wounds. External signs of infection are often scarce and may lead to incorrect stand vitality valuation. Modern devices, such as the PiCUS 3 Sonic Tomograph, can be used for non-destructive decay assessment. We assessed decay in two intensively managed Norway spruce (Picea abies L. Karst.) stands in order to identify the reliability of sonic tomography in tree vitality assessment. We hypothesize that the tomograph assessment is more accurate than the visual assessment for detecting the extent of decay damage in Norway spruce stems. The sample trees were first visually assessed without additional equipment. In the second phase, the same sample trees were measured with the PiCUS 3 Sonic Tomograph. In the last part of the study, the sample trees were assessed from the tree stumps following the clear-cut. We identified a relationship (p-value < 0.001) between the tomograph assessment and the stump assessment when major decay was present. We did not discover a relationship between the visual assessment and stump assessment, indicating that evaluating the decay from external signs is inaccurate according to our results. Our data also indicate that the tomograph is not able to detect the early stages of decay damage, since it has no substantial effect on the wood structure. [ABSTRACT FROM AUTHOR]

Survival of live retention trees is a key issue for stand-scale applications of natural-disturbance-based silviculture. We explored the survival of 3255 trees in 102 cut areas (mean size 2.3 ha) in Estonia for 6 years, focusing on spatial variation and preadaptation of the trees. Altogether, 35% of the trees died during the study period, contributing 4.4 [m.sup.3] of downed dead trunks and 1 [m.sup.3] of standing dead trees per hectare. The annual mortality rates declined over time. The main survival determinants were tree species (higher for hardwood deciduous trees), diameter (species dependent), position relative to forest edge (higher for trees near current or former forest edges), retention density (positive), and exposure (negative). The results suggest that (1) green-tree retention can effectively increase the abundance of large shade-tolerant trees, but it is equally important for producing deadwood; (2) larger individuals, former interior-forest trees near current forest edges, and preadapted trees in open conditions should be preferably retained; (3) there is no obvious necessity to modify tree-retention techniques for tree survival according to geographical region or forest site type. La survie des arbres vivants laisses a la suite d'une coupe a retention variable est le principal probleme lorsqu'une sylviculture basee sur les perturbations naturelles a l'echelle du peuplement est appliquee. Nous avons etudie la survie de 3255 arbres dans 102 parterres de coupe (taille moyenne de 2,3 ha) en Estonie pendant une periode de six ans en portant une attention speciale a la variation spatiale et a la preadaptation de ces arbres. Dans l'ensemble, 35 % des arbres sont morts pendant la duree de l'etude, ce qui a ajoute 4,4 [m.sup.3]/ha de gros debris ligneux au sol et 1 [m.sup.3]/ha d'arbres morts sur pied. Le taux annuel de mortalite a diminue avec le temps. Les principaux facteurs expliquant la survie etaient l'espece d'arbre (meilleure pour les feuillus durs), le diametre (fonction de l'espece), la position relative a la lisiere boisee (meilleure pres des lisieres, anciennes ou presentes), la densite de retention (relation positive) et l'exposition (relation negative). Ces resultats impliquent : (1) que la retention d'arbres vivants peut effectivement augmenter l'abondance de gros arbres tolerants a l'ombre, mais qu'elle est aussi importante pour produire du bois mort, (2) qu'il serait preferable de conserver de gros arbres situes anterieurement a l'interieur de la foret, mais pres d'une lisiere boisee actuelle, et des arbres preadaptes a un milieu ouvert et (3) qu'en termes de survie des arbres, il n'est pas justifie de tenir compte de la repartition geographique des arbres a conserver, ni des types de stations ou ils sont etablis. [Traduit par la Redaction], Introduction Variable retention cutting (VRC) is the main stand-scale application of natural-disturbance-based silviculture, which, by emulating the effects of natural stand-replacing disturbances, incorporates biodiversity considerations in forest management (Franklin et [...]

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. [ABSTRACT FROM AUTHOR]

In 2007, three mature hemi-boreal stands were selected from Järvselja forest district, South-East Estonia to establish one-hectare-large test plots for the international inter-comparison experiment of radiation models (RAMI). All trees with a stem diameter at breast height greater than 4 cm were mapped and measured in the field. In summer 2019, the forests were inventoried again. Here we present a summary of changes that occurred in the forest structure – mainly growth and mortality. In the birch stand basal area G has increased from 23.3 m2 ha-1 to 28.2 m2 ha-1 in the upper layer and the number of trees N has decreased from 654 to 565 ha-1. In the upper layer of spruce stand G has increased from 30.9 m2 ha-1 to 35.4 m2 ha-1 and N has decreased from 774 to 724 ha-1 and N substantially decreased in the lower layers from 912 to 577 ha-1. In the pine stand G has increased from 28.3 m2 ha-1 to 29.1 m2 ha-1 and N decreased from 1116 to 971 ha-1. The three test stands can be used now for validating remote sensing data-based estimates of forest inventory variables at single tree level. 2007. aastal rajati Järvseljal kolm ühe hektari suurust katseala, kui kaardistati ja mõõdeti üle kõik puud simulatsioon eksperimentide korraldamiseks (Kuusk, et al., 2013; Widlowski et al., 2015). Need kolm puistut (vt fotod lisas 1) esindavad tüüpilist liitunud võrastikuga kuusikut, kaasikut ja siirdesoo männikut. Kaasikus oli tehtud 2004. aastal harvendusraie, 2018. aastal puhastati katseala alusmetsast, et valmistada ala ette maapealse laser skanneriga mõõtmisteks. Kuusikus ja männikus teadaolevalt viimase 30 aasta jooksul raieid tehtud ei ole. Katsealade (joonised 1, 3, 5) nurkade koordinaadid on mõõdetud diferentsiaal-GPS meetodiga peale mahamärkimist (tabel 1). 2019. aasta kordus mõõtmiste tulemusena ilmnes, et puistute rinnaspindala, keskmine kõrgus ning keskmise puu rinnasläbimõõt olid kasvanud (tabelid 2–4). Puude arv oli kahanenud kõigis puistutes, välja arvatud kaasikus, kus 2018. aasta puhastus raie käigus jäeti alles selleks ajaks 4 cm rinnasdiameetri saavutanud puud. Kuusikus saadi tulemuseks, et võrade raadiused olid võrreldes 2007. aastaga kahanenud. Kas tegemist on võra projektsiooni välispiiri erineva tõlgendamise või tegelikult toimunud muutusega, võiks edaspidi selguda 2013. (Kuusk et al., 2015) ja 2019. aastal tehtud maapealse laserskanneri mõõtmiste andmete analüüsist. [ABSTRACT FROM AUTHOR]

Since 1999, Estonia has conducted the National Forest Inventory (NFI) on the basis of sample plots. This paper presents a new module, incorporating remote-sensing feature variables from airborne laser scanning (ALS) and from multispectral satellite images, for the construction of maps of forest height, standing-wood volume, and tree species composition for the entire country. The models for sparse ALS point clouds yield coefficients of determination of 89.5–94.8% for stand height and 84.2–91.7% for wood volume. For the tree species prediction, the models yield Cohen's kappa values (taking 95% confidence intervals) of 0.69–0.72 upon comparing model results against a previous map, and values of 0.51–0.54 upon comparing model results against NFI sample plots. This paper additionally examines the influence of foliage phenology on the predictions and discusses options for further enhancement of the system. [ABSTRACT FROM AUTHOR]

The availability of a large amount of data from reliable sources is important for forest growth modelling. A permanent plot where trees are repeatedly measured provides a clearer picture of stand alterations. Various factors, including forest management, affect forest growth and accuracy of its assessment. In Estonia, mean height as a regression height prediction at mean square diameter is commonly used in forest management practice. Alternatively, dominant height can be used. The main advantage of using dominant height instead of mean height is that the growth of dominant trees is not so strongly affected by stand density (thinning). The aim of our research was to investigate the difference between mean height and dominant height when used as stand height. The research was based on the Estonian Network of Forest Research Plots (ENFRP). As a result, we found that the average mean height change was significantly greater in the case of thinning when compared to undisturbed stand development, whereas, the average dominant height change in the case of thinning compared to undisturbed development was less significant. As a side result, we developed a regression model that can be used for calculating the dominant height of the main tree species using stand attributes (mean height, quadratic mean diameter and density) with a residual standard deviation of 0.466 m. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

• Tree growth dynamics during 40 post-drainage years were described using mixed models. • Ditching response maximum was ca. 800 mm2 year−1 and reaction time 16 years on average. • Growth response varied depending on pre-drainage tree size, growth rate and stand diameter. • The response was weaker, but reaction time was shorter, in larger trees compared to smaller ones. • Growth trend was affected more by a specific reference ditch than the closest ditch. Wood production in peatland forests is often associated with management of site hydrology that aims to improve soil moisture status and stand growth. Silvicultural outcomes of ditching activities vary greatly among drained sites, therefore new data and modelling approaches are necessary for better understanding of forest growth dynamics on a tree-level and a long-term scale. A mixed-effects model estimating growth response to initial ditching performed 40 years ago in Ongassaare region (northeast Estonia) was developed using basal area increment data derived from ring-width series of 287 Scots pine trees from 39 stands. The model indicated that ditching response was up to around 800 mm2 year−1 on average; this level of drainage-induced additional increment was reached 16 years after treatment. Pre-drainage tree diameter, mean stand diameter and radial growth rate were among the significant predictors, therefore the results suggest that tree size, stand growing stock and site quality or microsite conditions before the ditching are affecting post-drainage tree growth. Smaller trees experienced greater growth response; however larger trees responded to the treatment faster than smaller ones. Ditching therefore induced changes in stand structure by decreasing tree size variation. Ditching response was more pronounced in stands with smaller pre-drainage diameter, faster growing trees reached the maximum response values quicker. Trees closer to the drainage ditch responded slightly more intensively to changing site conditions, however, this relationship was significant in the case of a reference ditch (one of the ditches surrounding a forest stand, selected according to the topography of the landscape) but not the nearest one. Drained peatlands are very diverse in terms of pre-treatment site conditions, stand history and ditch network design, therefore additional data from extended network of sample plots would be necessary for updating the developed model to make it more applicable for further use (e.g., predicting forest growth and yield). [ABSTRACT FROM AUTHOR]

The functioning of complex forest ecosystems is intimately related to their structural properties. Tree mortality is a major driver of forest stand dynamics and therefore plays an important role in the formation of forest structure. Data from the Estonian Network of Forest Research Plots (ENFRP) was used to estimate the mortality probability of silver birch trees (Betula pendula Roth) by using logistic models. In this study several spatial and non-spatial variables were tested to determine the most important mortality explanatory factors. Additionally, thinning variables were defined and implemented into the mortality models, to examine whether thinning practices could modify the stand structure and density, then leading to a lower mortality rate. The results of this study showed that tree mortality models that included either a five-year diameter growth rate (id5) as a measure of tree vitality, or the tree relative diameter (drel) as a measure of competition, or both these two variables, were substantially better than any models not including these variables. In addition, any measures of spatial aggregation (agg) and species proportion (sp) within the zone of influence markedly improved the model predictions, though the mortality probability of trees declined where there was higher aggregation and species mixture. Our results also suggested that if thinning were conducted around the birch trees, depending on the thinning intensity, the number of neighbors is effectively reduced, and consequently the competition load within the influence zone decreases, leading to healthier growth and lower mortality rates of the shade-intolerant birch trees. We thus recommend to adopt thinning regimes in mixed forest stands to foster tree species diversity, and at the same time provide adequate growing space for birch trees within the stands. This will improve the forest structure and increase the adaptive capacity of forests, which is increasingly important under changing climatic conditions. [ABSTRACT FROM AUTHOR]

Afforestation on reclaimed mining areas has high ecological and economic importance. However, ecosystems established on post-mining substrate can become vulnerable due to climate variability. We used tree-ring data and dendrochronological techniques to study the relationship between climate variables and annual growth of Scots pine ( Pinus sylvestris L.) growing on reclaimed open cast oil shale mining areas in Northeast Estonia. Chronologies for trees of different age classes (50, 40, 30) were developed. Pearson's correlation analysis between radial growth indices and monthly climate variables revealed that precipitation in June-July and higher mean temperatures in spring season enhanced radial growth of pine plantations, while higher than average temperatures in summer months inhibited wood production. Sensitivity of radial increment to climatic factors on post-mining soils was not homogenous among the studied populations. Older trees growing on more developed soils were more sensitive to precipitation deficit in summer, while growth indices of two other stand groups (young and middle-aged) were highly correlated to temperature. High mean temperatures in August were negatively related to annual wood production in all trees, while trees in the youngest stands benefited from warmer temperatures in January. As a response to thinning, mean annual basal area increment increased up to 50 %. By managing tree competition in the closed-canopy stands, through the thinning activities, tree sensitivity and response to climate could be manipulated. [ABSTRACT FROM AUTHOR]

A generic regression model for above-ground biomass of forest stands was constructed based on published data (R² = 0.88, RSE = 32.8 t/ha). The model was used 1) to verify two allometric regression models of trees from Scandinavia applied to repeated measurements of 275 sample plots from database of Estonian Network of Forest Research (FGN) in Estonia, 2) to analyse impact of between-tree competition on biomass, and 3) compare biomass estimates made with different European biomass models applied on standardized forest structures. The model was verified with biomass measurements from hemiboreal and tropical forests. The analysis of two Scandinavian models showed that older allometric regression models may give biased estimates due to changed growth conditions. More biomass can be stored in forest stands where competition between trees is stronger. The tree biomass calculation methods used in different countries have also substantial influence on the estimates at stand-level. A common database of forest biomass measurements from Europe in similar to pan-tropical tree measurement data may be helpful to harmonise carbon accounting methods. [ABSTRACT FROM AUTHOR]

Structural indices and characteristics have often been employed for assessing different aspects of forest stands. In order to assess the performance of such measures in forest sample plots of different size and shape, the current study is based on a data set for a relatively large (1 ha) silver birch dominated stand, and five simulated planar point patterns (a Poisson process, two clustered and two regular patterns) with similar intensity of points distributed on an area equal to the silver birch stand as reference stands. The analyses was based on repeated samplings of the stands, with randomly placed circular or square shaped plots of different sizes, with area ranging from 0.007 to 0.636 ha. Similar centre positions were considered for plots of different shapes, but the locations of the plot centres differed with size, so that plots of different sizes were able to cover the maximum possible area of reference stands. Some structural indices accounting for one or four nearest neighbours, and also the Point-pair correlation function was then quantified for each random sample plot. We used standard deviation and the differences of the mean estimates from the expected values to assess the sensitivity of the structural measures to the size and shape of sampling plots. The results indicated the significant effect of plot size and shape on structural indices. The correlation between plot size and estimates precision was positive, and small plots, regardless of their shapes, showed big variation among them while circular plots often provided more accurate estimates. Even though, as expected, expanding the plots increased the precision of the neighbourhood-based indices' estimates (spatial measures), and also resulted in inaccurate estimates for some reference stands, depending on the arrangement of trees/points within that stand. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Post-mining restoration sites often develop novel ecosystems as soil conditions are completely new and ecosystem assemblage can be spontaneous even on afforested sites. This study presents results from long-term monitoring and evaluation of an afforested oil-shale quarry in Estonia. The study is based on chronosequence data of soil and vegetation and comparisons are made to similar forest site-types used in forest management in Estonia. After site reclamation, soil development lowered pH and increased N, K, and organic C content in soil to levels similar to the common Hepatica forest site-type but P, total C, and pH were more similar to the Calamagrostis forest site-type. Vegetation of the restoration area differed from that on common forest sites; forest stand development was similar to the Hepatica forest-type. A variety of species were present that are representive of dry and wet sites, as well as infertile and fertile sites. It appears that novel ecosystems may be developing on post-mining reclaimed land in Northeast Estonia and may require adaptations to typical forest management regimes that have been based on site-types. Monitoring and evaluation gives an opportunity to plan further management activities on these areas. [ABSTRACT FROM AUTHOR]

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A preface to the book "Forestry Studies/Metsanduslikud Uurimused" is presented.

The dynamics of the above-ground biomass production of a grey alder plantation on abandoned farmland was investigated during 11 years after establishment. In the 12-year-old stand, the total biomass of the above-ground part of the stand was 68.8 t dry matter (DM) ha-1 and the current annual production (CAP) was 14.0 t DM ha-1 year-1. The predicted mean annual increment (MAI) reached is maximum at the age of 16 years, which indicates bulk maturity (the stand age when CAI = MAI) and appropriate rotation time for obtaining maximum biomass production. In the case of short-rotation forestry, initial stand density should not be higher than 6500-6000 trees per hectare. Below-ground biomass accounted for 18 and 16 per cent of total stand biomass at a stand age of 5 and 10 years, respectively. The biomass of the nodules was estimated at 155 ± 63 kg DM ha-1 and the biomass of the fine roots was estimated at 870 ± 130 kg DM ha-1 in the 10-year-old grey alder stand. Of the fine roots, 80 per cent and almost all nodules were located in the upper 0-20 cm soil layer in both the 5-year-old and the 10-year-old stand. The value of leaf area index increased with stand age, ranging between 1.38 and 5.43 m2 m-2 during the development of the stand. Specific leaf area varied in different years from 11.1 to 13.5 m2 kg-1. [ABSTRACT FROM AUTHOR]

Abstract: In general, forests in Estonia are characterized by great variability, not only in protected areas but in commercial forests as well. The data needed for the derivation and calibration of growth models can be obtained by continuous observation of permanent growth plots (also known as longitudinal studies) or by establishing chronosequences with temporary plots distributed over a wide range of growing sites, densities and ages (also known as cross-sectional studies). A compromise may be achieved by a system of “interval plots” (also known as a short-time series: series which covers a short time). Since the measurement interval is a period of undisturbed growth, it is possible to measure change rates as in a longitudinal study and at the same time cover a wide range of initial conditions as in a cross-sectional study. Numerous models of stand growth have been derived from re-measured sample plots. This study, which uses the data of 142 five-year intervals from 134 unmanaged Scots pine stands, compares six different model combinations involving algebraic difference equations and fixed time-step increment equations. New stand-level diameter and basal area increment equations and a tree survival model which showed close correspondence with the existing stand-level model for Estonia were developed. The main advantage of the use of algebraic difference equations over the fixed-step increment equations is the ability to use flexible time steps. However, the projection intervals should not deviate too much from the time steps of the measurement data. An important constraint when using the algebraic difference equations is to avoid long-term predictions in one projection sequence. [Copyright &y& Elsevier]

Ecosystem management assumes that management practices based on natural disturbance patterns are likely to preserve both natural biodiversity and ecosystem functions. Ecosystem management thus combines traditional natural resource management and forestry practices together with classical notions of protection that are focused on sustaining a naturally evolving ecosystem. Increased knowledge and understanding of natural disturbance dynamics in boreal forest ecosystems allow for the creation of a template for sustainable forest management that is based on mimicking disturbances that are thought to contribute to the biodiversity of the ecosystem. The observed trends of natural development are discussed in this paper. Permanent sample-plot data are used to develop a conceptual model of stand succession following natural disturbance. The distinctive characteristics of disturbances that are relevant to forest management planning are identified and modelled. [ABSTRACT FROM AUTHOR]

Examines three general methods for construction of site index equations for Pinus sylvestris using permanent plot data in Sweden. Comparison of growth functions with the construction methods; Results of the difference equation method; Indications of a changed growth pattern.

In light of the difficulties in stand volume estimation of natural forests, we analyzed height–diameter relationships and derived a set of height estimation equations for volume estimation for naturally developing forest ecosystems, using the Järvselja old-growth and the Laeva commercial forest in Estonia as a case study. This contribution presents an approach to model individual tree height–diameter relationships for Scots pine, common aspen, silver and downy birch, Norway spruce, black alder, gray alder, linden species, European ash, Norway maple, deciduous species and coniferous species in multi-size and mixed-species naturally developing stands in Estonia. Single-tree-level data were collected in 2013. Two methods were used to obtain stand-level data: whole surface inventory and partial surface inventory. To model the height–diameter relationship in naturally developed mixed-species forest stands in order to predict single tree height based on observed diameter at breast height, we applied nonlinear mixed models where we applied the Chapman–Richards and Näslund models as fixed-effects and the influence of the species contribution at the sites as random effects. The fixed-effects followed a set of criteria: (1) height starts at h = 1.3; d = 0; (2) the applied functions are monotonically increasing with a clear inflection point and 3) the fixed-effect model has an asymptotic value) in a naturally developed mixed-species forest. [ABSTRACT FROM AUTHOR]

• As early as 5 years after clear-cutting a young stand was a weak C-sink. • Over a measurement period C budget was −0.011 t C ha−1. • Temperature and drought conditions greatly affect forest C-uptake. Growth of CO 2 concentration level has strong interactions with forests. Forests are able to sequester carbon (C) through photosynthesis and can help to mitigate the effects of climate warming, as well as to reduce the CO 2 concentration in the atmosphere. Drought and other extreme weather conditions play a key role in ecosystem functioning and the C-cycle. The eddy covariance (EC) method can be used to better understand forest ecosystems CO 2 exchange by directly measuring net carbon and water fluxes. In our study, EC results for measurement of fluxes between the atmosphere and forest canopy are reported for the study period from May to August 2018 in Järvselja, Estonia. Stand-replacing disturbance (clear-cutting) took place in April 2013. The young forest stand is dominated by Norway spruce (Picea abies) and birch (Betula spp.). Findings so far include (1) a C-budget for the study period that showed a slight C-sink status; (2) net ecosystem exchange (NEE) was −0.0084 µmol m−2 s−1 indicating C-uptake during the measurement period; (3) in May, June, July and August, NEE was −0.027, −0.015, 0.001 and 0.006 µmol m−2 s−1, respectively; (4) NEE fluxes are lower in drought conditions and are affected by temperature that averaged 15 °C. [ABSTRACT FROM AUTHOR]