Matti Sirén

Harvesting damage caused by thinning of Norway spruce in unfrozen soil

Two harvester working methods and two types of forwarder equipment (tracks and chains) were compared with respect to harvester productivity, logging residue on strip roads, rut formation, and logging damage in the thinning of two Norway spruce stands in Southern Finland. In the normal harvester working method, trees removed further away from the strip roads were processed outside the strip roads. In the protective method, the harvester operator processed as many trees as possible on the strip road and turned some of the treetops parallel to the strip road. The protective harvester working method increased harvester time consumption by approximately 5%, but a higher proportion (86–92%) of the total logging residue potential was brought to the strip roads. The logging residue mass obtained to cover the strip roads was approximately 14–19 kg/m2. According to the recommendations for forestry practice in Finland, damaged trees should not exceed 4% of the number of the remaining trees, and ruts deeper than 10 cm should not exceed 4% of the total length of the strip road network. In our study, the proportion of damaged trees clearly exceeded the limit. After two to four forwarder passes, the proportion of deep ruts generally remained below that threshold. Neither logging damage nor rut depth differed between the harvester working methods. The prerequisites for a successful thinning operation performed on unfrozen soil are favorable weather, soil, and stand conditions. On dry soils with high bearing capacity, ruts remain shallow and the proportion of deep ruts is low. Furthermore, a high amount of logging residue decreases rut formation.

Damage to saplings in mechanized selection cutting in uneven-aged Norway spruce stands

Abstract Damage to 0.5–2.5 m saplings in selection cuttings in uneven-aged Norway spruce stands was studied in three stands in Finland. Harvest removals were 96–122 m3ha−1 or 32–41% of initial basal area. Harvesting was carried out with one-grip harvester and forwarder in March–April 2007. The strip road network had been established in previous cuttings. Before harvesting, trees higher than 2.5 m were measured and mapped with coordinates. Saplings 0.5–2.5 m were measured on circular sample plots of 10 m2 on a square grid, where line and plot intervals were 7.07 m. Trees to remove were selected with a computerized tree selection procedure and marked before cutting. Factors affecting the probability and severity of injury to an individual sapling were studied with logistic regression models. Percentage of injured saplings was 17.6, 29.8, and 61.0%, depending on study stand. Stem breakage was the most common type of injury. Distance of the sapling from the nearest strip road, sapling height, harvested basal area within 25 m of the sapling, and the distance to the nearest remaining tree were statistically significant factors in the model of the probability of injury. In the model for the severity of injury, only the distance from the nearest strip road and the sapling height were significant. Saplings near strip roads were vulnerable during both cutting and forwarding, and they often ended up under slash or logs. Development in working methods and machinery are potentially effective in reducing sapling damage in selection cuttings.

Equipping a Conventional Wheeled Forwarder for Peatland Operations

Abstract In Finland, peatland logging is generally conducted during the winter due to the inherently low soil bearing strength under unfrozen soil conditions. Mild winters the past several years have raised the issue of operations on unfrozen peatlands. Modifying wheeled logging equipment such that it was able to operate cost-effectively on sensitive sites and then switch back to normal, base machine specifications at other times would be a significant advantage. The mobility and rut formation of a conventional 8-wheeled forwarder was studied with four different sets of chain/track equipment. Additionally, the forwarder was equipped with a rear, add-on axle resulting in a 10-wheeled forwarder. That modified forwarder was tested with the widest set of tracks on an abandoned peat field and on a pine bog. Results indicate that the forwarder modifications significantly increased mobility and decreased rut formation on the test soils. On the pine bog, the 10-wheeled forwarder had the best mobility and the least rut formation of all equipment tested.

Co-operation and integration in wood energy production.

Abstract The aim of the study was to investigate the effects of co-operation and integration in large-scale wood energy production. The total procurement cost and yield of forest chips (small-sized trees and logging residues) delivered to the consumption plant were calculated for three harvesting strategies. In Alternative 1 individual stands were harvested. In Alternative 2 the harvesting of smallsized trees and logging residues was integrated within forest holdings. Alternative 3 included both co-operation between neighbouring forest holdings and the integration of harvesting. In integrated harvesting, small trees and logging residues were jointly chipped at intermediate storages. The study material consisted of forest management planning information and forest maps, in digital form, for privately owned areas totaling 15000 ha, of which 3720 ha was forest. GIS data and costs models were used in constructing a production model for a power plant consuming 100000 m3 of forest chips per year. Integration raised the harvestable small energy wood yield by 30.5% (Alternative 2) and 31.5% (Alternative 3). The corresponding values for all forest chips were 12.9% and 13.3%. The average cost of forest chips was 3.4% lower in Alternative 2 and 4.9% lower in Alternative 3 than in individual stand harvesting. The cost effects on the total production cost of small tree chips were greater than on the production cost of logging residues. Co-operation and integration broaden the raw-material base for wood energy and make the supply more even.

Wheel rut measurements by forest machine-mounted LiDAR sensors – accuracy and potential for operational applications?

ABSTRACT Soil rutting caused by forest operations has negative economic and ecological effects and thus limits for rutting are set by forest laws and sustainability criteria. Extensive data on rut depths are necessary for post-harvest quality control and development of models that link environmental conditions to rut formation. This study explored the use of a Light Detection and Ranging (LiDAR) sensor mounted on a forest harvester and forwarder to measure rut depths in real harvesting conditions in Southern Finland. LiDAR-derived rut depths were compared to manually measured rut depths. The results showed that at 10–20 m spatial resolution, the LiDAR method can provide unbiased estimates of rut depth with root mean square error (RMSE) < 3.5 cm compared to the manual rut depth measurements. The results suggest that a LiDAR sensor mounted on a forest vehicle can in future provide a viable method for the large-scale collection of rut depth data as part of normal forestry operations.