Latvia is one of the forest-richest countries in Europe. Very often in young forest stands of spruce admixture of coniferous or deciduous trees are taking place. During the growth trees suffer from influence of different risk factors. Damages in mixed stands depend on chosen mode and intensity of economic activities. Forest management cannot be imagined without creating the infrastructure (roads, ditches, etc.). However, the development of infrastructure may cause an effect of fragmentation and lead to changes in the forest structure. The aim of the research is to analyze influence of forest spatial features on the sanitary state of mixed stands of spruce. In 2011 and 2012 mixed stands of spruce younger than 40 years were investigated in all regions of Latvia. Nineteen stands were measured and surveyed and 80 sample plots were arranged. With the help of Geographical Information System (GIS) data base of the State Forest Service of Latvia the forms of forest plots (regular or irregular), as well as location of neighbouring infrastructural objects and location of mixed stands in forests were stated. In unnaturally created regular form plots damages of risk factors usually tend to be larger than in those, which have been created naturally. With the credibility of 95%, linear connection between occurrence of damages caused by browsing and intensity is relevant (r=0.937 is greater than r0.05=0.575), as well as occurrence and intensity of damages caused by Lophophacidium hyperboreum Lagerb. (r=0.999 is greater than r0.05=0.575).

The aim of the study is to ascertain how different compositions of stand species affect the work of the harvester in commercial thinning under Latvia’s conditions. The data of the harvester – time-tracking files (*.drf) have been used as a basis for the study, where productivity is expressed as the prepared amount of round timber in cubic meters in a unit of time – an hour (m**3 hE-1). The data were collected from 100 commercial thinning areas which were divided into three types depending on the composition of the species: pure pine stands, pure spruce stands and deciduous tree mixed stands (mixed with coniferous trees). All the data for the study were collected in the forests managed by JSC ‘Latvia`s State Forests’. By summarizing the data, it has been established that in pure pine stands the average volume of the stem to be removed is 0.092 m**3, in mixed stands – 0.085 m**3 and in pure spruce stands - 0.068 m**3. The research demonstrates that the harvester showed its highest productivity while working in pure pine stands – 3.96 m**3 hE-1, the second best result was achieved in the mixed stands – 3.67 m**3 hE-1, but the lowest rate was demonstrated in pure spruce stands – 3.09 m**3 hE-1. Significant differences were observed in the productivity of the harvester between pure pine and pure spruce stands. Comparing the calculations of standard deviations in the harvester productivity, it can be seen that they are the biggest in mixed stands, while the lowest rate is demonstrated in pure spruce stands.

Norway spruce (Picea abies (L.) Karst.) is economically important tree species, vulnerable to impact of different biotic (cervids, bark beetle etc.) and abiotic (wind, wet snow etc.) factors and their combinations, expected to increase in frequency and/or magnitude in future due to climate changes. The aim of the study was to characterize occurrence damages in Norway spruce stands in Latvia. Data from 635 National forest inventory sample plots were used in the analysis, thus providing the information primarily on the non-lethal damages, since the dead trees in most of the cases would be removed from the stands in sanitary cuts. Damages were reported for 11.6 ± 1.1% of spruces from total basal area of spruces in the assessed pure and mixed stands. Admixture of other tree species or soil (group of forest types) had no significant effect on the proportion of damaged spruces. Also, no statistically significant differences in dimensions were observed between damaged and undamaged trees. The major cause of damages was browsing (three quarter of damaged spruces, in contrast to only one-quarter of the rest of the trees) and the highest proportion of damaged spruces were in stands in the age group 41 – 80 years, significantly differing from that in younger (up to 20 years) stands, demonstrating both the preferences of cervids to a certain dimensions of spruce as well as accumulation of damages over time.

The aim of this research was to study the effect of the stand composition on the density of pine and spruce wood growing on former arable lands. Sample areas are located in mixed mature pine- and spruce-prevailing stands in Leningrad region, Russia. For the reliable determination of the basic density of spruce and pine wood, selection of model trees was carried out and cores were taken. Based on the data obtained from stems of 36 model trees from 3 sample plots, conversion equations were calculated to determine the basic density of wood. The measurements of the spruce and pine wood density were processed using variational statistics. The results have shown that the pine forms a more homogeneous wood than the spruce. On former arable lands, spruce has a denser wood than pine under the same growth conditions. The stand composition has a significant effect on the density of spruce rather than pine.

In Latvia, P.abies (L.) H. Karst stands occupy about 18% of the total forest area (3.01 million) forming pure and mixed stands. Regardless of the main goals, productivity of the future forest stands must be preserved; therefore, it is very important for forest management to identify risk factors. P.abies often suffers from various risk factors. The aim of the research was – to assess the sanitary state of Picea abies (L.) H. Karst in Oxalidosa, where the area of forest stands has been restored both anthropogenically and naturally. Selected young stands are located in Limbazi district of Latvia. Empirical data was collected in 5 spruce stands with the total area of 9.2 ha in Oxalidosa. In total, 67 sample plots were installed with radius of 3.99 m, measuring 799 trees. Diameter was measured for all trees in the sample plot. For sanitary state of P.abies young stands characterization damage caused by biotic factors was assessed visually after four-point scale: health tree (0), minor damage to 25% (1), moderately damaged 26 – 50% (2), severely damaged or dried – from 51% (3). Damage caused by P.abietina and browsing was found in several stands, while damage produced by P.abietina larvae was detected only in one pure stand. Occurrence of browsing damage is 10 – 28%, while damage intensity – 7.7 – 21.8%. There are significant differences between occurrence of browsing damage (p=0.001) and also between damaged tree damage intensity (p=0.003). Nature of browsing damage depends on the size of pure and mixed stand area, the location in forest massif and adjoining territory.

The influence of coniferous stand composition on the density of pine (Pinus sylvestris) and spruce (Picea abies) wood is considered in this work. Processing of a large quantitative material of wood cores with the use of the ANOVA and rank analysis made it possible to reveal the influence on the macrostructure of wood of the quantitative representation of pine and spruce in the stand. In the pine part of the stand, the correlation of the wood density with the zones of early and late xylem is weak or medium. There is no wood density correlation with the width of the annual ring for stands with different shares of pine. In pine-prevailing stands with a share of pine 80% – 100%, there is a weak but reliably straight relationship between wood density and the size of late wood zone and an inverse relationship with early zone of xylem. For forest stands with a smaller part of pine participation, the relationship between these indicators is medium and reliable. For spruce, we observe a close relationship between the density of xylem and the parameters of its macrostructure in all its variants of participation in mixed coniferous plantations. In most of the studied mixed stands, the density of wood in spruce is not significantly differentiated and more homogeneous.