Mechanized First Thinning Trials of Pinus radiata and Pseudotsuga menziesiiPlantations

Rom

1989

23 S.

16 Abb., 15 Tab., 7 Lit. Ang.

Bandaufführung

11832

96998

Thinnings represent one of the major problems of Italian forestry. So far, the high cost of the manual work has often brought about an incorrect managment of forest stands, thus considerably increasing their exposure to fire hazards. The present paper deals with mechanized first thinning trials in four conifer stands: two of Pinus radiata D. Don located in the Grosseto district, and the other two, of Pseudotsuga menziesii (Mirb.) Franco, in the Florence district. The adopted type of thinning was mixed (systematic + selective) for three of the areas involved, with removal of some 40 % of trees, in one stand being carried out the systematic thinning only with removal of 25 % of trees. Technical and economic results of the harvestig trials are reported. The mechanization degree varied in relation to the site morphology and tree espacements. In fact, with espacements less than 2,5 m the selective thinning can be only performed by motorsaw, excluding trimming, which proves very expensive. As concerns the slope, 30 % shows to be the maximum level beyond which thinning operations cannot be fully mechanized. The yields of mechanized felling, trimming and piling ranged between 2.115 and 3.612 m3/h, and those from the same operations carried out by motorsaw between 1.045 and 11.700 m3/h. The considerable difference between the latter two yields is due to the fact that trimming and piling were conducted in one of the two areas only. Skidding without previous concentration proved a yield of 18.635 m3/h, while what from both concentration and skidding varied between 2.680 and 4.022 m3/h. The yield of logging and piling for pallets resulted 6.109 m3/h, while logging and piling for sawlogs for the pulping industry showed more or less steady yields (from 3.750 to 3.883 m3/h). Debarking yielded from 3.862 to 5.643 m3/h, and chipping from 8.486 to 10.038 m3/h. The costs of the final products, per cubic meter, ranged as follows: sawlogs for the pulping industry, from 26,470 to 55,040 liras; debarked sawlogs, from 34,405 to 66,705 liras; chips; from 24,380 to 49,830 liras. The cost of sawlogs for pallets resulted 24,035 liras/m3. Regarding the obtainable assortments, certainly conditioning harvesting techniques, whole-tree chipping proves the less expensive conversion process, to be preferred to sawlogs, whenever market conditions allow it.