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bucking and crosscutting, delimbing). The comparison results are shown in Table 10.
The difference between largest and smallest DBH is more than three times and generally decreases by increasing the tree DBH size. Observing the Main work time we noticed that the variability in productivity is generally increasing with increasing tree dimensions by CTL and decreases by MM technology. Results are partly influenced by number of samples, which is for larger DBH classes very small.
Delays – Prekidi rada
The share of unproductive time has a large impact on the efficiency of both CTL and motor manual technology. We separated delays (worker, machine and organization related – for instance organization delays, disturbance time) from the entire non-work time. The distribution of recorded trees regarding delays is shown in table 11.
Table 11 shows large average differences in recorded delays between the two analyzed technologies (6,64 versus 32,07 percent). In both cases recorded delays increase with DBH class. The ratio between CTL and MM shares decreases with increasing DBH class. Consequently, we assume that this is an important reason that the comparative advantage of CTL technology decreases in the same direction (with increasing DBH class). We cannot confirm that delays are more likely to occur in single vs. multi-trunked trees for either CTL or MM technology.
DISCUSSION AND CONCLUSIONS
RASPRAVA I ZAKLJUČCI
We have expected higher differences in productivity observing only Main work time between the analyzed technologies in favor of mechanized cutting. Past research reported the average ratio of 1:7 in favor of mechanized cutting in conifers stands. The results show that in observing the average mechanized Main work time (direct contact with a tree), CTL is only 3 times more efficient than theMM cutting.
The ratio between MM and CTL productivity is higher in the coniferous stands, which is logical; delimbing represents a significantly larger proportion of the working time by MM cutting in young coniferous stands than in hardwood stands. Glöde (1999) reported that harvester Valmet 892/960 had delimbing problems in pine stands with the average branches diameter more than 7 cm and in birch stands with branches more than 8 cm in diameter at a place of cutting off (delimbing). He concluded that most delays occurred in working element processing the tree.
We analyzed the reasons for spending additional time for cutting and processing of multi-trunk trees. In the case of forked trees the operator had many problems with tree processing. The following situation was very often recorded: the tree crown begins immediately after the twig, which is an additional obstacle because the processor head does not develop a sufficiently high velocity for a successful delimbing. In the situation of multi-trunked trees difficulties are even greater. Operator must drop the tree to the ground by every point /occasion/ where tree forks and after that re-hold it, consequently prolonging the delimbing time. The feeding rollers and cutting knives of harvester head do not develop sufficient force for the successful cutting off branches.
In comparison the MM cutting of multi–trunked tress does not cause as many problems; additional delimbing has to be done which in terms of working technique and productivity does not differ from the single-trunked processing. The most time-consuming work element is therefore delimbing. It can be concluded that the mechanized cutting has higher suitability in the stands dominated by single-trunked trees with thin branches and short crown.