2. LOCATION OF THE CASE STUDY

The study was carried out in a private forest enterprise in Carinthia, the southernmost federal state of Austria. The forest estate amounts to approximately 2 500 ha; the stands - between 400 m and 1 450 m in altitude - are stocking on different types of soil developed from granitic rock. The harvesting operations observed were regeneration fellings, chosen to stimulate existing natural regeneration, which were part of planned harvest cuts.

Forest accessibility is provided by approximately 55 m of road per ha with a formation width of 6 m, carriageway width of 4 m, and types of construction corresponding to the usual forest road standard in Austria. Considering the utilization of forest roads by construction cranes it should be mentioned that the axle loads and gross vehicle weights of cranes appropriate for logging operations should not be higher than those of loaded timber trucks. The bearing capacities of forest roads might be exceeded by the high axle loads of such vehicles during wet seasons, and therefore this has to be considered when planning logging and hauling operations.

The two study areas where regeneration felling took place were located between 470 m and 480 m in altitude and the terrain varied from 15% on the one area to between 20% and 30% slope gradients on the other. But it is important to emphasize that flat terrain is not a precondition for the use of construction cranes. Just the opposite is true: their use will be recommended for harvest cut areas where natural regeneration has to be preserved; the slope gradient or rocks and other obstacles require that felled trees or logs be transport "lifted" to the forest road where they will be handled by the wood processor or manually delimbed and bucked by means of chain-saws.

In this enterprise, articulated four-wheeled skidders were usually used for logging up to a slope gradient of about 20% uphill and 40% downhill. Above these slope gradients cable systems were used.

When the construction crane was first set up, in study area A, only assortments were transported according to the weight and height of the trees; otherwise the permissible load weight would have been exceeded and the young trees forming the natural regeneration - with an average age of 15 years and 4 to 10 m in height - might have been badly damaged because of the limited hook height of the crane (see Photo 1).

Photo 1. Stand before harvesting.

At the second study area, B, the natural regeneration was much smaller (about 2 m) so whole trees could be transported by the crane, except that there was the danger of exceeding the permissible load weight which would have caused delays during the logging phase; this would have made it necessary to cross-cut the trees once. In this case the fellers cross-cut the trees at a height of about 12 to 16 m depending on the lowest branches so that no delimbing with the chain-saw was necessary at the felling site.

Table 1 gives the stand characteristics for the study areas before harvesting.

Table 1. Stand characteristics of the study areas.

(Values per hectare apply to full stocking.)

Table 2 shows the different conditions for logging at both study areas.

Table 2. Logging conditions.

At study area A only assortments, mainly long logs, were extracted; at study area B trees, tree tops and long logs were transported by the construction crane.