The case study was carried out in the Republic of Austria at two harvesting areas with 105-year-old and 75-year-old stands of spruce and Picea abies, respectively, amply supplied with natural regeneration in the understorey. The volume harvested on both areas amounted to approximately 178 m3 with an average tree size of about 2 m3 at the one area and 1 m3 at the other.
Two harvesting methods were observed: the modified full-length method and the whole-tree method. Modified full-length method means that delimbing and topping of the trees take place at the felling site and that bucking (or cross-cutting) is carried out after transfer to the forest road. With the whole-tree method, felling and trimming are done in the stand. Skidding is to the skidding corridor or the forest road, where processors are used for mechanical conversion.
The trees or assortments were logged by a construction crane and were piled on the forest road thereafter. If the whole-tree method is applied a wood processor will usually be used for further processing. The team for logging by construction crane consists of the crane operator and two assistants. The crew increases by an operator if a wood processor is used simultaneous-ly.
Time studies were carried out only for the logging phase to assess logging performances which can be expected under particular conditions. The stated productivity rate for the wood processor has been obtained from previous time studies carried out under comparable conditions.
The average productivity rate of the logging operation, excluding setting up and vehicle moves between the locations for setting up, amounted to about 12.5 m3 per hour with average load volume of 1.2 m3 and average logging distance of 30 m.
The cost of the logging operation was US$ 8.48/m3 and increased to US$ 11.11/m3 if time involved in setting up the crane and lunch-breaks were also considered.
At study area B where the whole-tree method was applied, the production increased to 15.5 m3 per hour, which corresponded quite well with the production given for the wood processor of about 15 to 17 m3 per hour according to the average size of assortments. The wood processor usually operates simultaneously with the construction crane so that its performance is limited by the logging operation of the crane.
By using highly mechanized timber harvesting, the felling was carried out by chain-saws. Since the performance rate of felling is very different from that of the logging and processing machines, felling has to be completed by the time the other phases begin in order to permit the use of logging and processing equipment to almost full capacity.
However, due to high rental costs of machines the simultaneous operation of logging and processing requires more planning and supervision in order to avoid longer waiting periods between phases.
A construction crane combined with a wood processor is recommended especially for use in small-scale operations in order to prevent logging damage to the natural regeneration and also for salvage cutting operations after windthrow.
Further time studies should be undertaken in order to find the most suitable types of construction cranes for logging and to optimize operating conditions and the sequence of operations in general.