Volume 22, numéro 1, 2011

EN :

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.

EN :

The aim of this study was to explore the capability of airborne laser scanner (ALS) data to explain the variation in field-measured variables representing timber quality within square 0.25 ha grid cells in a mature conifer forest in the southeast of Norway. These variables were the mean ratio between stem diameter at six m above ground and the diameter at breast height (R _D6 ), the volume of saw logs (V _SL ), the proportion of saw logs relative to the total volume (P _SL ), the ratio between tree height and diameter at breast height (HD), mean basal area diameter (D _g ), and crown height (CH). Each of these variables was modeled using a mixed modeling approach. Model fit was expressed by the Pseudo-R ² , and were 0.85, 0.50, 0.78, 0.57, 0.74, and 0.58 for the respective quality variables. Furthermore, much of the residual error could be attributed to the different forest stands from which the grid cells originated even though we used field-observed tree species proportions as auxiliary information. It was concluded that more auxiliary information is needed to estimate models that are general across stands, but that the relationships between ALS-data and the quality variables considered here seem strong enough to be utilized for example to prioritize between stands in relation to harvest when specific quality distributions are sought.

EN :

Sorting logs for stiffness in the woods using acoustic devices mounted on harvesters and processors could improve the allocation of logs to their most appropriate processing destinations. Estimating spatial changes in acoustic velocity in felled stems, based on a limited number of measurements, will be essential if they are not to unduly impact harvesting or processing productivity and costs.

The effect of five variables (length from butt, bark percentage, moisture content, green density, and oven dry density) and four velocity measurement approaches (time of flight [TOF] across the tree bole, resonance of the full tree length, resonance of the first 3 m butt log segment, and resonance of a log segment between 6 and 9 m above the butt) on the ability to estimate spatial changes in acoustic velocity were evaluated in felled Douglas-fir stems from five stands in southwestern Oregon.

Distance from the butt was a significant predictor of acoustic velocity along the stem. TOF acoustic velocity measured across the bole had little value in predicting the longitudinal resonance acoustic velocity of a section of the tree. Full tree length resonance acoustic velocity, or single log acoustic velocity (either 3 m butt log or 3 m log 6 m above the butt) were found to be statistically significant and strongly correlated predictors of acoustic velocity of a section of a tree (R ² ranging from 0.68 to 0.89). The models were found to be stand-dependent, indicating a possible need for calibration for each stand to be harvested.

EN :

Although only a few harvesting systems today intentionally remove bark prior to transporting logs to the mill, little is known about how much bark is lost during harvesting operations at different times of the year. Depending on where you are located in the forest to mill supply chain, the presence or absence of bark can be seen as a cost or a benefit. Understanding the magnitude of bark loss and the factors that affect it should lead to minimization of the costs and maximization of the benefits.

Quantification of seasonal bark loss (expressed as a percentage of the surface area of the stem) for two commercial tree species was conducted monthly over a 10-month period. All assessments were carried out on Douglas-fir and ponderosa pine harvesting operations that were using mechanized processor heads with chains over rubber feed wheels. Over 400 stems were assessed.

There was a substantial (up to five times) increase in bark loss during late spring and early summer compared with the winter season. We were also able to show that the amount of bark loss is species dependent, with Douglas-fir incurring more than twice the bark loss than found for ponderosa pine. It is possible that the distribution of bark loss along the stem is also species dependent; we found greater bark loss towards the top of the stem in ponderosa pine than towards the bottom of the stem, but no such trend for Douglas-fir.