The harvesting system applied when a construction crane operation is used in combination with a wood processor is a highly mechanized timber harvesting system. The work phases are as follows:
· Processing (delimbing, cross-cutting, storage)
The harvesting method of this particular harvesting system (felling by means of chain-saws, logging by construction crane and processing by wood processor) is the whole-tree method.
Emphasis was given to the construction crane operation because the use of construction cranes for logging was previously not known and therefore data such as productivity rates were unavailable.
The felling phase was not included in these studies because it had already been done when the logging and processing phases started. In order to perform all work phases simultaneously a high range of planning and organization is required; furthermore felling might be disrupted by the logging operations and vice versa. But the felling operation must be carried out very carefully if natural regeneration is to be preserved. Directional felling cannot be done in a hurry and might be hindered by the assistant hooking the assortments. In the second case when the logging process is disrupted by felling trees, the logging operation might result in higher costs, and logging with cranes becomes unprofitable.
Another reason why the felling process was not observed is that the fellers worked on a private contract basis which means their performance per hour is of no importance to the enterprise because they are paid a certain amount per unit - in this case cubic metre of timber - after finishing the job.
After the felling phase, logging by the construction crane begins. At study area A the all-terrain crane was set up at two locations on the forest road; at study area B the crane was set up, as mentioned above, about one boom length from the road, into the felling site.
One assistant hooks the trees or assortments with log tongs and after their transport to the forest road by the crane a second assistant unhooks the load. All trees or assortments are piled on the forest road or next to it, so a wood processor or a timber truck with a loading crane can pick them up.
If the whole-tree method is applied, a processor is usually used after the logging phase is done by the construction crane. There are different types of processors available but so far only one-grip processors were used in combination with a construction crane for logging.
The major advantage of the one-grip crane processor is that after lifting the trees further processing is done by the same unit which has a rotating unit suspended from a hydraulic loading crane. This rotating and swivelling unit permits the operator to pick up the trees from almost any position, to process them in any position and to place them around the machine so that different assortments can be stored in separate piles (see Photo 8). Another advantage of one-grip processors compared with two-grip processors is that handling the trees is much easier and consequently there is less mental strain on the operator.
On the other hand, a disadvantage of one-grip processors is their net weight which requires both a higher weight of the carrier vehicle and higher stability of the crane. Despite the disadvantages of two-grip processors, compared to one-grip processors, their use is conceivable because of reasonable costs.
Photo 8. Site after processing operation. The different assortments and the debris are piled separately.