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.

The aim of the research is to find out changes in productivity depending on the diameter of the tree to be cut as well as the most important factor influencing the reduction of productivity using small size forest machines in thinning in Latvia. The equipment used in the study – both the harvester and the forwarder is Vimek. The results of the research confirm the appropriateness of the exact technique in thinning if diameter of the harvested trees is 3 to 30 cm. The average productivity of the harvester achieved with a harvester head Keto Forest Eco (option 2) in Norway spruce stands with 8 cm weighted average tree reached 9.59 m**3 hE-1, in deciduous tree stands with 9 cm weighted average was 10.17 m**3 hE-1, but in Scots pine stands with 12 cm average weighted tree diameter reached 10.19 m**3 hE-1. By using the Keto Forest Eco Harvester head according to the thinning productivity figures, no significant difference among the tree species was detected. For the forest owner to predict the theoretical productivity of the harvester, it is possible to apply the equation R = K + KD * D, that is statistically significant, R2 =0.85. This equation is applicable to thinnings when the diameter of thinned trees is between 4 and 25 cm. Forwarder’s average productivity in thinned stands is 8.63 m**3 hE-1.

The paper covers analysis of pre-commercial thinning performed in private forests over the period of 2007–2017. Since 2007, permanent and considerable European Union subsidies for pre-commercial thinning have been available; resulting in a significant increase in area of thinned young stands in private forests. The aim of this research is ascertain pre-commercial thinning activity depending on the type of forest owner (individuals, legal persons or local municipality), forest stand type (forest stand or plantation) and origin (natural or artificial) as well as the forest owner’s intention to apply for European Union subsidies. Data analysed were obtained from Forest State Register – national data base, managed by state authority State Forest Service and continued analysis comprise two main topics – ascertain amount and type of young stands owned by different type of private forest owners and amount and type of conducted pre-commercial thinning. In comparison with other type of forest owners, legal persons have significantly higher amount (47%) of young plantation forest and forest stands from the total forest stands area. The highest intensity of thinning was conducted in plantation forests of artificial origin owned by legal and physical persons, also forest stands with artificial origin owned by physical persons. The current period for European Union Rural development programme will be over in 2020; therefore, it is important to analyse the existing approach of granting subsidies to forestry and find the improvement necessary for the planning period from the year 2021.

The topicality of the study is determined by the increasing demand for sanitary felling services currently mainly provided by manual work. Harvesting using hand-held motor instruments is a physically hard work whose costs are increasing rapidly, but labour availability is declining. In sanitary cuttings, additional complications are caused by the use of conventional machinery in harvesting, which necessitates the creation of wide (4 m) technological corridors and significantly increases the proportion of damaged remaining trees in a stand (according to past studies, a set of middle-class forest machines in thinning of spruce stands results in 4–5% of damaged trees, but in pine stands – in approximately twice less damaged trees than in spruce stands). The compact class forest machines in thinnings result in mechanical damage to not more than 1% of remaining trees. During field trials in sanitary felling 9329 trees were felled. The average productivity, working in one shift, is 5.35 m**3 hE−1 with average stands 10 cm. The cost of harvester’s productive hour is 92 € but of a forwarder it is 78. The compact class forwarder creates significantly smaller impact on the soil by reducing ruts depth and soil compaction, which is especially important in sanitary fellings and extraction of seed trees in regenerated areas.