© iForest -Biogeosciences and Forestry IntroductionNorway spruce is the second most abundant tree species in Latvian forests, occupying 0.52 million hectares, and nearly 0.14 million are second age class (21-40 years old) forest stands (Latvian State Forest Service 2011). Therefore, it is critical to assess the management risks in growing stand volume now, because it is these stands that will comprise the majority of the cutting volume in 40-60 years. Spruce is a species quite vulnerable to biotic and abiotic factors; therefore its cultivation is increasingly associated with high-risk levels. One of the most widespread causes of Norway spruce stand damage is development of large spruce bud scale colonies.The first cases of Norway spruce damage were observed in 2009 in middle-aged stands on drained soils. In August of 2010, monitoring by Riga Forests revealed 24% of the stands were damaged, and 10% of Picea abies stands were reported dead. Management made the decision to avoid further spruce bud scale propagation by felling 300 ha of Norway spruce forests in sanitary clear-cuts . Physokermes piceae Schrnk. belongs to the Coccidae family, order Hemiptera, and are characterized by sexual dimorphisms, with a high ability to adapt to a parasitic lifestyle on host plants (Rasina & Rupais 1994). Adult females are globular with a pronounced curvature, shiny, and brown to reddishbrown in color. Female length averages 3.5 mm, width 3.0 mm, and height 3.5-4.0 mm.Males are winged, average 1 mm long, and rarely encountered (Ozols 1985). Males have a discernable head, chest and abdomen, three pairs of legs, and one pair of wings (Graora et al. 2012). The species develops one generation per year. Immature stages winter at the base of terminal buds, less often on needles. In May, the instar larvae move to the base of new buds by old bud fissures. By the end of May or beginning of June, the females have already developed. Settling on the trunk and twigs, individuals suck sap through the bark vascular tissue. At the end of June or beginning of July, the insects lay eggs beneath themselves, and soon die (Ozols 1985). Several studies report one female lays 800-3 000 reddish eggs (Novak 1974, Turguter & Ülgenturk 2006, State Forest Service 2010. Pink first instars, called "crawlers" hatch in July, and attach themselves to new buds or the underside of needles. In October, crawlers molt into the second instar, and change color from pink to brown. The second instar larvae continue to suck sap, and subsequently overwinter on the branching parts or the lower side of the spruce needles. In spring, a small portion of the overwintering population travels to the needles, where in May the individuals pass through prepupal and pupal stages, developing into winged males (State Forest Service 2011, Lazdins et al. 2011. After wintering, most second instars attach themselves among the budding forked branch apices, where molting occurs, and round yellowish females emerge that gradually darken, and are easily noticeable (State Forest Service 2010.Sp...

ABSTRACT:In management of young forest stands, it is often the case in forestry that several risk factors, biotic, abiotic and anthropogenic ones, have to be dealt with. An anthropogenic factor is of great importance in management of forests, because humans, using ecosystems for their needs, still have to maintain the spatial structure of the forest and prevent the worsening of the health state. Covering all territory of Latvia, empirical material was gathered in 25 pure stands. To find out how neighbouring stands impact the young forest stands of spruce, the location in forest array was detected. In identifying the risk factors, attention should be paid to the shape of compartment and its location in forest array. A correlation between the occurrence and intensity of damage caused by cloven-hoofed game is relevant r fact = 0.988 > r crit = 0.088 with 95% probability. Also the occurrence and intensity of Lophophacidium hyperboreum Lagerb., and damage by Heterobasidion spp. are relevant r fact = 0.991 > r crit = 0.062 and r fact = 0.981 > r crit = 0.088 with of 95% probability.

Climate change will cause winds to strengthen and storms to become more frequent in Northern Europe. Windstorms reduce the financial value of forests by bending, breaking, or uprooting trees, and wind-thrown trees cause additional economic losses. The resistance of trees to wind damage depends on tree species, tree- and stand-scale parameters, and root-soil plate characteristics such as root-plate size, weight, and rooting depth. The root-soil plate is a complex structure whose mechanical strength is dependent on root-plate width and depth, as the root system provides root attachment with soil and structural support. In Latvia, the common aspen (Populus tremula L.) root system has been studied to develop a belowground biomass model, because information about root system characteristics in relation to tree wind resistance is scarce. The aim of this study was to assess the root-plate dimensions of common aspen stands on fertile mineral soil (luvisol). Study material was collected in the central region of Latvia, where pure mature (41–60 years old) common aspen stands were randomly selected, and dominant trees within the stand were chosen. In total, ten sample trees from ten stands were uprooted. The diameter at breast height (DBH) and tree height (H) were measured for each sample tree, and their roots were excavated, divided into groups, washed, measured, and weighed. The highest naturally moist biomass values were observed for coarse roots, and fine root biomass was significantly lower compared to other root groups. All root group biomass values had a strong correlation with the tree DBH. The obtained results show that there is a close, negative relationship between the relative distance from the stem and the relative root-plate depth distribution.

Forest engineering students need to develop their competence in order to ensure a sustainable working environment in the relevant   sector of economy. The aim of the study was to clarify the dynamics of the development of the students’ competence in the learning process. The methodological basis of the study included the analyses of the relevant publications in the context of competence and adult education. The authors’ personal reflections and work experience at the Forest Faculty of Latvia University of Life Sciences and Technologieswere taken into consideration. To assess the development of students’ competence in the forest engineering studies a survey was carried out. Within the framework of the study and as the result of improved adult studies, there was a significant improvement of students` competence in the field of forest engineering. The self-assessment of competence at the end of the course was higher than at the beginning of it.

SUMMARYClear cutting and selection cutting are final felling methods. Clear cutting are often used in Latvian forest. The disturbance of biological rhythm in clear cutting areas occurred for several years. Whereas selection cutting is more environmentally friendly, efforts should be made to apply it more in practice. Objectives of this research are to analyse the regrowth conservation after gradual felling in Hylocomiosa forest stands with a different species composition and determine tree health. For dendrometric indicators and gradual selective felling intensity characterization, twelve sample plots with an area of 500 m2 were established in both forest stands. Plots were surveyed before and after the gradual selective felling. In order to perform an analysis of regrowth, 92 small inventory plots with a radius of 2.82 m were evaluated. Regrowth trees were counted (conifers from 0.1 m height and deciduous -0.2 m) and their height was measured, as well as root rot infection was verified. In the Norway spruce mixed stand (7S3P145) felling intensity was 52% but in the Scots pine mixed stand (5P5S105) respectively -49%. After felling trees regrowth number of losses account are 53 and 68%. The average height of spruce regrowth trees in both stands after felling was fallen but average height of birch and Scots pine regrowth increased. The differences of regrowth preservation between tree species during selection cutting were significant (p=0.016<α=0.05). Root rot was not detected in the mixed Scots pine stand, but in spruce stand it was found in 33% of cases.