The purpose of the study was to determine the productivity of multi-stem cutting of pulpwood and delimbed energy wood, along with the time consumption of cutting work phases performed with a tracked, forestry equipped excavator as the base machine and a Naarva EF 28 as the harvester head. On the basis of the time-study data collected, per-stem time-consumption and productivity models were prepared for the multi-stem cutting of delimbed wood. In the multi-stem cutting time-consumption model, productivity was explained in terms of stem volume and harvesting intensity (number of stems removed per hectare). Productivity was expressed in solid cubic metres per effective hour (m3/E0h). In the time studies, the multi-stem cutting productivity per effective hour was 12.8 m3/E0h and 233 stems/E0h, on average. Cutting productivity per effective hour (m3/E0h) increased as the stem volume of trees grew. On the time-study sample plots, the lowest and highest values recorded for multi-stem cutting productivity per effective hour were 8.7 m3/E0h and 19.9 m3/E0h, respectively. The corresponding stem-number figures for the extremes of cutting productivity were 347 and 183 stems/E0h. On average, the harvester head processed 1.9 stems per grapple cycle, while grapple loads processed via the multi-stem method (at least two stems in the grapple at a time) accounted for 57% of all time-study data. In total, 2,267 stems were cut in the time studies consisting of 71 m3 of pine pulpwood and 53 m3 of multi-stem delimbed energy wood.
Calculations using the time-consumption model have shown that when the harvesting intensity was tripled from 800 to 2,400 trees/ha, the productivity of multi-stem cutting per effective hour increased by about one solid cubic metre, whereas increasing the stem volume from 23 dm3 to 89 dm3 doubled the cutting productivity per effective hour. If the results of this study are generalised or compared with those of other studies, the amount of material and the effects of the harvesting site and operators must be taken into account. The results indicate that the productivity of the excavator-based harvester and the Naarva EF 28 harvester head was very high: at the same level as, or even better than, that of wheeled harvesters equipped with a conventional multi stem harvesting equipment. The machine concept studied is a highly viable option for integrated harvesting of pulpwood and energy wood. Operation of the machine unit was problem-free throughout the time studies, with no interruptions caused by breakdowns. Moreover, the harvesting quality met the recommended standards.
Key words: Integrated harvesting, accumulating harvester head, excavator-based harvester, first thinning, pulpwood, multi-stem handling, delimbed energy wood.