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).

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.

Browsing damages are becoming more common due to almost doubling of population densities of cervids in Latvia during last 20 years; however, the figures are still lower than those observed in western and northern European countries. Consequently, the frequency of damages in young stands is increasing, too. Protection against browsing becomes more difficult, as the trees grow older; also the bark-stripping may result in a long-term deterioration of stem quality. Therefore, the aim of the study was to assess the factors affecting bark striping damages in pole-stage Norway spruce stands. Data were collected in 4 sample plots in damaged Norway spruce stands in western Latvia, measuring the tree parameters: height, diameter, branch characteristics and damage parameters: size, proportion from the stem circumference. Results of the modelling reveal that both damage parameters were significantly influenced by the branch length and thickness in the whorl closest to the breast height and the size of damages – also by breast height diameter of the tree. It suggests that increasing productivity of trees would not reduce the browsing problem. Since the silvicultural goal is the reduction of the size of branches, especially in bottom-log of the stem, protection against bark-stripping needs to be developed and cervid population densities controlled to reduce the problem.

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.