Impact of a variety of forestry machine types on soil compaction is evaluated in this study according to the measurement of soil penetration resistance at 0 to 80 cm depth. It is concluded in the study that soils with poor bearing capacity (PBC), comparably small penetration resistance and organic layer thicker than 5 cm are less vulnerable to soil compaction. The use of small-size forwarder Vimek 610 allows to reduce soil compaction to an insignificant level in comparison to the control sites, and most or ruts disappear within a few days in PBC conditions. Whereas John Deere 810E, which belongs to the middle-size class of forwarders, significantly compacts soil through the whole measured depth in similar conditions. Rottne F10B and John Deere 810E forwarders represent the same weight category, and soil compaction due to the use of these machines on soils with moderate bearing capacity (MBC) is similar too; however, on soils with weak (WBC) and good (GBC) conditions results are different, mostly due to a different amount of extracted roundwood in both trials. Tracked forwarder was used only in GBC conditions and the results demonstrated significant compaction only down to 22 cm depth. The trials confirm that the depth of the intensity of impact depends on the weight of the machine and amount of material extracted; however, additional measurement data are necessary to characterize the impact quantitatively in different conditions.

Tracked forwarders is one of the solutions for the forest soils with poor bearing capacity providing ability to use well-known technology for reasonable cost to improve accessibility of forest resources. Tracked forwarders are not common in forest nowadays and only a few models are produced serially. The ProSilva F2/2 is a new middle-class forwarder, whose frontal tracks are replaced with big tires, ensuring large contact surface, increased mobility of the machine and significantly reduced mass without loosing the load capacity (15 tonnes). The aim of the study was to evaluate productivity, soil impact and cost of the roundwood forwarding using the ProSilva F2/2. The study was conducted in Finland. Productivity (time per crane cycle, split into operations and loads), load size, depth of ruts and soil compaction were estimated during the study. According to the study results, the average productivity is 16 m**3 per hour (driving distance to a landing site 200 m, driving speed 2.8 km hE-1, average load 9.7 m**3). The productivity can be significantly increased by more efficient utilization of the load capacity and by using gripper with the tilt function. The length of ruts on peat soil (56 m haE-1) does not exceed the permitted threshold values in Latvia. The compaction of soil took place mainly in topsoil, no changes in soil density were observed in deeper soil layers. The prime cost of forwarding according to the preliminary estimates is 2.5 € mE-3 if the annual production is at least 62000 m**3. Utilization rate is important to keep forwarding cost low.

The aim of the study was to compare the productivity and logging costs using the small class harvester Vimek 404 T5 in thinning of birch plantations and young coniferous stands. It was found in the study that due to a lower fuel consumption, maintenance costs and initial investment, the cost of a working hour of the harvester Vimek 404 T5 is significantly smaller than the cost of a working hour of the middle class harvester. The study confirmed that Vimek 404 T5 is a suitable harvester for thinning in a birch plantation; the study also confirmed the previous conclusions about the main advantages of Vimek harvester compared to a middle class harvester in the first thinning – low fuel consumption and costs of maintenance, high productivity and equipment compactness, which allow to reduce the strip road area. The average productivity for Vimek 404 T5 in birch plantation was 6.2 m**3 per productive hour, but in young conifer stand the productivity was 4.9 m**3 per productive hour. The average stem volume in the birch plantation was 0.06 m**3, but in conifer stand 0.05 m**3. Productivity for the same dimension trees in the birch plantation is not significantly different from the data obtained in the thinning of the coniferous stands.

The aim of the study was to determine the impact of the harvester cutting head feed roller type on the mechanical damages of processed roundwood timber in post manufacturing. The study presents the comparison of the gentle Moipu plate wheel rollers and conventional feed rollers having bigger spikes (hereinafter named - conventional feed rollers). The total amount of segments processed with the gentle Moipu plate wheel rollers was 2199, whereas the amount of segments processed using the conventional feed rollers was 5308. When processing roundwood with the gentle feed rollers, in the 1st flow 8.2% of timber was rejected as substandard due to defects. The corresponding figure in the 2nd flow was 5.2% of the material in which the damage in the form studs was caused by the feed rollers. When processing the timber with conventional feed rollers, the percentage of the damage – dents caused by these rollers in the 1st flow was 26.7%, in the 2nd flow – 43.7% and in the 3rd flow only 2.7%. Using the method of characteristics proportion comparison, significant differences have been observed between feed rollers (t = 17.8 is greater than t sub(0.05;∞) = 1.96).

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.

Fire is a frequent disturbance in hemiboreal forests that in Latvia affects mostly Scots pine (Pinus Sylvestris L.) stands. Increased forest fire risk is predicted in future as a result of climatic changes. Therefore the aim of our study was to assess Scots pine regeneration after forest fire in different forest types and with different regeneration methods. Tree height was measured and browsing damage assessed seven years after the forest fire in six different forest types, where planting and natural regeneration (in a clearcut and without management) occurred in compartments randomly selected from a list of stands severely affected by forest fire. The height of Scots pine was significantly affected both by forest type and regeneration method. Notable advantages of planting based on tree height were found in wet mineral soils and peat soils. Trees on poor (dry, wet, peat) soils were higher in natural regeneration after clearcut than in natural regeneration without clearcut. The density of Scots pine trees was significantly affected by the forest type but not by regeneration method (planting, natural regeneration, natural regeneration after the clearcut). The most abundant tree species in natural regeneration after clearcut in all forest types was silver birch (Betula pendula Roth.). The height of silver birch exceeded that of Scots pine in all analyzed soils in clearcut areas except Vaccinososphagnosa forest type, emphasizing the importance of thinning to ensure a successful development of Scots pine stands.