Forest Ecosystem models are diagnostic tools to assess and understand ecosystem processes. Conflicting interests such as simplicity, observability and biological realism must be addressed to ensure a well balanced modelling approach. Because field observations are usually only available for short time periods or for a limited number of locations, models are important to extrapolate in space and time. The key to a successful modelling approach relies on finding the appropriate scale but is often limited by the availability of input data. In the practice of forest modelling, it is often necessary to produce meaningful outputs on the basis of rather weak information. In this paper we discuss spatial and temporal scaling issues within empirical modelling. Following the case studies the paper demonstrates how models address cross-scaling problems as they are relevant for the required data as well as the decision making and implementation process of specific end user needs.

Key words: forest modelling, scaling, end user

The authors conducted a comparative study of continuous timing and work sampling, as applied by different observers. Twelve researchers were split into two groups and carried out the same study, switching method every half an hour. The study has lasted 3 hours, corresponding to 6 iterations (3 iterations per method). Statistical analysis of data confirmed that both methods may determine elemental breakdown with the same accuracy. Observer-induced variability had a minor effect, and only on those time elements that were short and occurred less frequently. Error increased as the study progressed, as the likely result of observer fatigue. Again, this trend was significant for short elements and not significant for longer ones. This study may offer a warning against over-detailing elemental breakdown. Work cycles should be split in as many elements as strictly necessary for achieving the specific purpose of the study. Splitting them in too many elements just for the sake of description is counterproductive, because it places an excessive strain on the observer and it may increase the risk of errors. A simple study design will facilitate replication by a number of different researchers, regardless of method.

Key words: time studies, methodology, accuracy, work sampling, operations

Price systems for industrial roundwood vary considerably between countries depending on the number and size of the sellers and buyers and government interactions. Roundwood is a heterogeneous raw material meaning that different species, qualities and dimensions have different value potential for different end-uses. In the long term, price levels and price systems offer signals for roundwood production to forest owners who are capable of considering the economic feasibility of different actions required to grow appreciated raw material. In the study, five different price systems, pricing by roundwood assortments (PbA), pricing by total volume (PbV), pricing by stem size fractions (PbSF), pricing by assortment fractions (PbAF) and pricing by log dimensions (PbD), were compared by using bucking simulations. Price systems were analysed by the relationship between sale value and wood paying capability (WPC) which is a residual value of a raw material to the wood buyer, after deducting all the reasonable costs of manufacturing, distribution, marketing and otherwise conducting a business. The analysis included performance of the price systems in different stand types and elasticity of the price systems against changed log-length demand. The PbV and the PbSF tend to produce excessive sale values for the stands where WPC was low, and exceedingly low sale values for the stands where the WPC was high. The sale values were divided more by the WPC of the stand in the cases of the PbA, PbAF and PbD.

Key words: bucking; price systems; roundwood markets; roundwood price; price-quality relationship

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.