Appropriate discount rate for forestry is still an issue for the forest economy. Therefore, it is significant to understand the importance of discounting, and how costs of forestry production process are valued. Forest regeneration and new stands tending costs are considered as investments; they are related to each particular stand. For that reason, the goal of this study was to compare how the value of this investment is growing at the bank deposit or 1 ha forest stand. The study examined the growth rate of two different tree species value with young forest stand establishment and tending investments depositing in the bank or the growth rate of compound interests. As discounting formula derived from a compounding formula, it would allow to find an appropriate discount rate for each timber species. High rates of compound interest cause a very rapid and unrealistic future value increase, while low rates cause slow value increase for a very long period represented by a common forest rotation; for that reason high discount rates used in forestry are not rational. Taking into account an income from intermediate cuttings, the value of timber species in comparison with the deposit significantly improves. Suitable discount rate determination in forest assessment is mainly determined by the species of wood productivity and cutting age. As it is hard to find two identical forest properties, each situation should be considered individually, taking into account and understanding the relationship between a growth rate of timber and compound interests, thus choosing an appropriate discount rate.

Reduction of agricultural production has led to abandonment of farmlands in Latvia. According to the Central Statistical Bureau, 1.4 million ha of lands, including 0.6 million ha of farmlands were set aside in 2008. Most of them transform into forests; however, information about the afforestation has been limited until recent years. The first field measurement based evaluation of forest stands on abandoned farmlands was implemented within the scope of the National statistical forest inventory (NSFI). The NSFI covers forests, farmlands, settlements, wetlands and other lands, providing valuable information about the land use and forest resources. According to the NSFI, total area of naturally afforested farmlands is 257,850 ± 3,606 ha with growing stock of 2,870.364 ± 239,088 m³. Naturally afforested lands occupy 4% of the total country area. The highest share of naturally afforested lands is in Ludza (11% of the total area) and Krāslava districts (9% of the total area). Birch (Betula pendula Roth) and grey alder (Alnus incana (L.) Moench) are the most common dominant tree species in naturally afforested areas (77,092 ± 1,861 ha and 40,285 ± 1,395 ha, respectively). In relation to the Kyoto protocol it is important to separate lands afforested before and after 1990. The total area of lands afforested after 1990 in Latvia is 170,890 ± 2,862 ha with total growing stock of 1,367.427 ± 125,482 m³ and annual increment of timber volume – 122,530 ± 10,513 m³.

One of the key factors affecting the formation of high-quality forest is thinning. Latvia's yearly budget of commercial thinning is not met; therefore, there are plenty of forests which are not thinned as planned and this leads to declining quality of forest stands. The timber processing industry needs significant excluded volume of timber, but forest owners are unable to maximize profits in future. Extensive logging of commercial thinning is hindered by economic factors and forestry regulations. Logging business is not satisfied with the productivity indicates and restricting forestry and environmental laws. The world's leading forest engineering firm offers a variety of forest harvester design and structural solutions. The first real use of commercial harvesters in commercial thinning in Latvia's conditions revealed several problems. The most important one is how to increase harvester productivity, while ensuring the quality of residual stands. To increase effectiveness of the logging machines and the proportion of commercial thinning, it is necessary to explore main factors affecting harvester productivity. This work aims to clarify the main pressures hampering harvester productivity and evaluate the quality of remaining trees in commercial thinning in Latvia. The main results are that during night productivity of harvester decreases by 12%, while marking trees to be cut down with fluorescent colour increases productivity of harvester at night by 15%. Productivity of harvester in thinning depends on average volume of harvested trees. These results of the work were obtained through various experiments on twelve different commercial thinning areas in Latvia.

This paper introduces the first test results to use laser scanning and high resolution digital colour infrared aerial image data to estimate average tree crown density at a sample plot level. General methodological framework based on two-phase sampling schemes, non-parametric estimators and satellite images as the auxiliary data sets was adopted for the use with airborne data sources. More than 400 circular sample plots were established and measured in a special research forest area near Kaunas, the central part of Lithuania. The tree crown density was visually estimated for every coniferous tree belonging to the 500 square m plot together with other conventional forest parameters. Two variants of digital colour infrared aerial images (ground sampling density 15 and 40 cm), LiDAR point clouds, based on 1 point/square m scanning density and two phase sampling approach with non-parametric k-nearest neighbour and most similar neighbour estimators were used to test the accuracies of tree crown density estimation at a sample plot level. Reliable estimates were found to be possible on pure coniferous stands only. Average tree crown density was estimated with the root mean square error around 17.5-18% at a sample plot level, bearing in mind average crown density around 64% for the whole study area. The estimates were unbiased. Integration of laser scanning based variables with the ones available from digital aerial images resulted in lowest estimation root mean square errors. Laser scanning based variables used as the auxiliary data set independently resulted in better estimation errors than the variables available from digital colour infrared images.

Scots pine (Pinus sylvestris) is Latvia's most economically important tree species. It accounts for 38% of the total forest area of Latvia. One of diseases affecting P. sylvestris is root rot caused by the fungus Heterobasidion annosum, which causes large economic losses. There is some evidence of Scots pine trees with higher levels of resistance but no absolutely resistant tree clones have been described so far. Many genes encoding peptides and proteins with direct or indirect antifungal activity have been described in various plant species, but only few of them have been studied in conifers. In our study we have utilised various approaches to research genetic aspects of Scots pine resistance to H. annosum. Here we present our initial results. Initially, H. annosum infection was determined in 300 trees and in a subset of twenty seven trees representing fifteen families (progeny of one mother tree) infection levels were quantitatively characterised. Candidate-genes were selected based on previously published research. Gene copy number variation (CNV) analyses were performed on selected samples. Copy number variation polymorphism was detected for a gene encoding a thaumatinlike protein analogues of which are described as potent antifungal proteins in other plants. As increased gene copy number can lead to increased gene product amounts in cells it is possible that an increased copy number of thaumatin-like protein is beneficial to the pine tree in respect to resistance against H. annosum and other pathogens. Further experiments need to be performed to investigate this in more detail.

The effect of growing conditions, age and stocking density on the amount of deadwood in the pine forest stands of Latvia was analyzed in this research. The material for studies was collected within the framework of the National Forest inventory of Latvia in the period 2004 to 2008. From databases of the National forest inventory the data about 1627 sample plots dominated by pine were selected and analysed. The total amount of deadwood (m3 haE-1) was compared among five forest edaphical rows - forests on dry mineral soils, forests on wet mineral soils, forests on wet peat soils, forests on drained mineral soils and forests on drained peat soils. Deadwood was also analysed in five age groups – young, middle age, premature, mature and over-mature stands, as well as in six groups of stocking density – small-density, sparse-density, middle-density, high-density, full-density and over-density stands. It was found out, that the growing conditions (p = 0.000 is less than α = 0.05), stand age (p = 0.000) and stocking density (p = 0.000) have significant influence on the amount of deadwood in pine forest stands. The highest amount of deadwood is in the pine stands on wet mineral soils – 18.6 ± 2.09 m3 haE-1. With increase of the stand age the amount of deadwood also increases and in the mature pine stands the amount of deadwood is 17.8 ± 1.58 m**3 haE-1. The amount of deadwood in the pine forest stands also increases with stocking density and in the over-density stands it is 21.6 ± 2.50 m**3 haE-1.

Large proportion of 30-50 years old spruce stands originated from overstocked plantations can be characterized by low growth potential and present serious problem to forest managers. Although according to legislation unproductive spruce stands can now be clearcut, possible alternative solution allowing a forest owner to remove only trees with the worst growth potential would be also welcome. To be able to recommend any silvicultural measures, information on the inner structural development of the stands is necessary. The aim of this study was to analyze temporal structure of several spruce stands that have originated from overstocked plantations and now belong to the 2nd (increased risk stands) or 3rd (unpromising stands) growth potential groups. Data for the study from seven sample plots located in Forest Research Station ''Kalsnava'' and thinned with different intensity were used. Tree diameter distribution, volume accumulation patterns and tree mortality were analyzed. Correlation between tree diameter and tree diameter difference in the observation period from 2000 to 2006 was weaker than in the observation period from 2006 to 2009, indicating further decline of growth potential. In most cases the major part of the volume was accumulated in the middle of the diameter class distribution. For most of the trees one or both sawlogs were of good or average quality. In order to develop optimal and profitable stand management model, the effect of different thinning methods in spruce stands of low growth potential should be studied in the future.

Experimental self-binding high-density fibreboard is produced of the grey alder (Alnus incana L. Moench) steam-exploded fibres without addition of synthetic adhesives. Milled grey alder chips are processed in steam-explosion unit by saturated steam under pressure of 3.2 MPa at temperature of 235 deg C for 1 min in a 0.5 l batch reactor. The steam-exploded fibres are pressed at 160 deg C temperature under 8 MPa pressure for 10 min in three steps. Properties, such as density, swelling in thickness, water absorption, bending strength, modulus of elasticity at bending, and internal bonding strength of the studied fibreboard samples are reported. Differences between the raw milled chippings and the exploded fibres are observed by scanning electron microscope. The study is focused on modified technical options of the steam-explosion unit supplied with two containers receiving different kinds of the exploded biomass farther used to obtain the hot-pressed boards. The cascade of the receivers is explained in a presently pending patent. The self-binding high-density fibreboard samples show the following properties comparable to commercial products: density of at least 1.35 g cmE-3, moisture content of 7.2%, swelling in thickness of 8.1%, water absorption of 3.2%, bending strength of 27 N mmE-2, modulus of elasticity of 6,259 N mmE-2, and internal bonding of 0.92 N mmE-2.

Black alder wood is suitable for production of high quality veneer and other uses, but doe to its small share in total forest area (3%) in Latvia its genetic improvement have not been a priority. Set of progeny tests, together 22.8 ha, have been established only in the last decade. First of them have reached the age of 8 to 10 years and are suitable for first assessment. Aim of our study was to evaluate potential of improvement of black alder using selection, based on progeny testing. Data from 4 open pollinated progeny tests of phenotypically selected black alder plus trees, located in central part of Latvia, each containing from 15 to 21 families, are evaluated, using breeding value as a criterion. Results reveal that selection of parent trees with the practically possible intensity (10%) yields notable improvement in height at the age of 8 to 10 years: from 10 to 32%. Parent trees of open-pollinated families S9, S14, S16 and 84115 that have superior productivity and above-average quality can be recommended for establishment of second-round seed orchard. Estimates of genetic parameter suggest that selection in black alder trials could be carried out with high accuracy and improvements are possible both in productivity and quality (branch thickness, stem straightness, occurrence of spike knots).

Icing notably increases the mass of a tree crown, causing damage to the tree. So far, a very limited number of studies have assessed the icing influence on coniferous trees, none of them in Latvia. The aim of the study was to assess the influence of tree parameters and recent thinning on the proportion of damaged trees and the type of damage in Scots pine stands. The study sites were located in the eastern part of Latvia, damaged in December 2012. In total, 98 pine dominated stands of different age were selected randomly. Eight (mean) plots per stand were established; in each plot, all trees larger than 2.1 cm were measured and the type of damage assessed. The above-ground biomass from 12 randomly selected stands (57 dominant trees) of different age was weighted with and without icing. The biomass of pine with icing exceeded that without 1.5 ± 0.27 times. The mean proportion of damaged trees in pine dominated stands was 26%; the proportion of broken trees peaked in the middle-aged stands (41 – 70 years old), but the largest proportion of pooled bent and uprooted trees was found in the young (11 – 20 years old) stands. The proportion of damaged dominant trees was affected by the slenderness coefficient – a higher proportion of such trees was found among more slender trees. The results suggest that the risk of icing damage could be reduced by silvicultural measures boosting individual tree stability.