6. STUDY METHODOLOGY AND ANALYSIS OF DATA

Work and time studies to assess the efficiency of felling and extraction operations were undertaken in accordance with generally accepted forest work study procedures (IUFRO 1995). The study methodology used for all time studies was cumulative timing exclusively, with the time for each work element subsequently obtained by subtraction.

Although the skidding machine operator was studied independently from other harvesting activities, information on other crew members was collected to support the analysis of time consumption and interpretation of the time distribution of work elements.

The postharvest assessment of environmental impacts associated with harvesting was limited to a survey of skidtrails in order to quantify soil disturbance caused by the operations.

6.1 Work and time studies on felling and extraction

Cutting comprises a set of activities undertaken to fell standing trees and prepare them for extraction. Extraction is defined as the process of moving trees or logs from the felling site to a landing or a roadside where they will be processed into logs or consolidated into larger loads for transport to the processing facility or other final destination (Dykstra & Heinrich 1996).

Depending on the harvesting system applied, these activities vary with respect to their frequency of occurrence. Nevertheless, a sequence of regular work elements can be found for felling that constitutes the normal work cycle. The same applies also to extraction. The normal work cycle comprises a sequence of work events that are repeatedly applied to every work object (IUFRO 1995). A work element is sub-division of a given work task and is delimited by break points. Depending on whether or not it occurs in every work cycle, a work element can be considered as a repetitive or an occasional element.

Only workplace time, which is defined as the portion of the total time that a production system or part of a production system is engaged in a specific work task (IUFRO 1995), has been considered in estimating production rates. Although meal time is part of the workplace time, it has been excluded from estimations because it varied considerably during the study.

Figure 7 shows the conceptual structure of work elements as generally applied in forest work and time studies. The nomenclature shown in the figure was used in this study.

Figure 7. Structure of workplace time concepts (Source: IUFRO 1995).

6.1.1 Work and time study on felling operations

The classification and percentage of workplace time, excluding meal time, as observed for each work element in felling operations can be found in Appendix 3 for both study sites, M38/SBLC and BL14/VFP. General data from the felling studies may be summarised as follows:

Note: Workplace time excludes meal time

* Trees crosscut only:

M38/SBLC: the tree was knocked when a neighbouring tree was felled

BL14/VFP: one tree was knocked down when a neighbouring tree was felled; the other was a natural treefall that could still be utilised

On average, the total workplace time per tree felled was 25.43 minutes for set-up M38/SBLC and 20.57 minutes at the Vanimo site for Subplot BL14/VFP. Total workplace time per tree felled serves as the basis for estimating production rates, treated in Section 6.2, and is to be distinguished from the time required to fell a single tree, shown in Table 8 for both study sites. The latter is used to compare felling operations between the two study sites and excludes times occupied in examining rejected trees and in cutting down hang-ups or crosscutting trees that were not felled.

Similar figures on the total time required and the time shares of the various work elements were found in a study of felling in Brazil (Winkler 1997). As in PNG, the study in Brazil involved conventional logging, with untrained fellers carrying out the work, and the trees were similar in size to those in this study, with an average volume of 5.6 m³/tree.

Although the chainsaw operators on Set-up M38/SBLC had seven and eight years of experience respectively, the total time required to fell a single tree was almost 24% higher than on Set-up BL14/VFP, where the three chainsaw operators observed had between 7 months and one year experience only and virtually no training. This difference was attributed to significantly more difficult conditions at Set-up M38/SBLC, where the topography was steeper, undergrowth was dense, the weather was more difficult (light rain and wind), and about 45% of the trees had vines and/or buttresses to be cut.

Vine cutting had not always been carried out prior to felling and therefore had sometimes to be done by the chainsaw operators. In addition, the higher shares of time spent on "site clearing" and "felling preparations" at M38/SBLC reflect the need for substantial removal of underbrush.

At BL14/SBLC the operators frequently changed duties with their assistants. Smaller trees were cut by the assistants, thus allowing the chainsaw operators to have a rest. At M38/SBLC the chainsaw operators seldom traded off with the assistants and, together with the difficult conditions, this resulted in lower average productivity in spite of the fact that the share of productive work time at M38/SBLC was more than 10% higher than at BL14/VLP.

Table 8. Comparison of tree felling times at the two study sites.

A general comparison of the time distribution of work elements observed in felling a single tree at the two study sites suggests the following:

· Cutting techniques of the more experienced operators with some training (see Section 3.3) resulted in a lower share of time spent on bucking and delimbing at M38/SBLC

· Use of improper felling techniques at BL14/VFP is evident from the time spent "cutting free the chainsaw", which was almost seven times higher than at M38/SBLC

· Vine cutting in advance as required under Key Standard 5 would have substantially improved felling productivity at M38/SBLC

6.1.2 Work and time study on timber extraction

Due to weather conditions at the Ania-Kapiura site, skidding operations were suspended during the period of this study so that skidding data could not be collected at M38/SBLC. Detailed information from the extraction time study at BL14/VFP can be found in Appendix 4. A general summary of data from the study is as follows:

The utilisable volume extracted at BL14/VFP differs significantly from the utilisable volume recorded during the felling study. This is because more than half of the trees in the extraction study were felled after the felling study had been completed. Skidding was scheduled to commence after felling operations were finished on the whole subplot area. However, weather conditions were about to change and extraction operations were started early in order to ensure that data on extraction could be obtained. To speed up the process of log extraction from the subplot area, a second crawler tractor was employed so that skidding could be completed before the weather made it impossible to continue.

On average, the time required per log skidded was 16.38 minutes for Sub-sample 1 and 24.40 minutes for Sub-sample 2. The second sub-sample occurred after weather conditions had already begun to deteriorate and the crawler tractors sometimes got stuck. The average skidding distance was also longer for Sub-sample 2. The total workplace time per log skidded, including both productive and supportive work elements, serves as the basis for estimating production rates as discussed in Section 6.2. The average work-element times required to skid a single log are summarised in Table 9.

Table 9. Distribution of work elements observed during the skidding study.

For Sub-sample 2 only the total time, number of logs skidded, and log volumes were recorded for each skidding cycle. Times were recorded when the tractor left the landing en route to the forest and when it returned to the landing, after which log diameters and lengths were measured and recorded. This was the only way two crawler tractors could be observed simultaneously with the available manpower.

6.2 Estimating production rates

Since productivity is defined as the rate of product output per time unit for a given production system, the production rates of a studied system can be estimated if time studies combined with measurements of the output of production have been completed.

6.2.1 Felling

Estimated felling production rates for the two study sites are based on the total time required to provide a certain volume of timber, regardless of whether a particular tree has been felled and crosscut, crosscut only, or rejected. Volume per tree harvested has been calculated by multiplying the average cross-sectional area of the stem by the stem length measured at the felling site. The cross-sectional area is based on diameter measurements, including bark, made at each end of the stem at the felling site. Time calculations are based on workplace time excluding meal time.

Table 10. Estimated felling production rates from the work and time studies.

Notes: 1) Volume per tree felled refers to utilisable volume measured overbark.

2) Productivity is measured as the utilisable overbark volume felled per hour of workplace time, excluding meal times.

Based on the hourly productivity values derived in Table 10 and an effective workplace time of 7 hours per day, excluding the lunch break, the average production rates measured during the study were 97 m³ per day at M38/SBLC, equivalent to 16-17 felled trees per crew-day, and 118 m³ per day at BL14/FVP, equivalent to 20-21 felled trees per crew-day.

However, the actual working time of the felling crews deviated quite considerably from the "ideal" seven hours per day, ranging between five and eight hours. In some cases work stopped early due to breakdown of the chainsaw. In other cases the felling crew decided to quit work after the volume had been cut that allowed them to meet their target daily wage under the piece-rate system by which they were paid.

6.2.2 Extraction

Estimated skidding production rates for the two sub-samples are based on the total workplace time, excluding meal time, required to extract a certain volume of timber. Data from the study are summarised in Table 11.

Table 11. Estimated extraction production rates from the work and time studies.

Notes: 1) Volume per load refers to utilisable volume measured overbark.

2) Productivity is measured as the utilisable overbark volume extracted per hour of workplace time, excluding meal times.

Based on the hourly productivity derived in Table 11 and an effective workplace time of 7 hours per day, excluding the lunch break, the average production rate measured during the study is 113 m³ per day, equivalent to 20-21 logs extracted per crew-day. Productivity for the two sub-samples shown in Table 11 provide an indication of performance levels that might be expected under dry weather conditions and skidding distances up to 500 m (Sub-sample 1), compared to those under wetter weather conditions and skidding distances up to about 1,050 m (Sub-sample 2).

6.3 Estimated wood recovery

Timber losses associated with felling and extraction at the study site of Subplot BL14/VFP were estimated by means of a wood recovery study. Wood recovery was calculated in terms of the volume of sawlogs extracted to the landing as compared to felled stem volume at the felling site. Losses caused by splitting of logs during felling and undiscovered decay in the stem were recorded immediately after felling. The only timber loss during extraction occurred when the tractor operator decided not to extract an unsatisfactory topped tree. Data from the wood recovery study are shown in Table 12. All calculations are based on volumes measured overbark.

Table 12. Estimated wood losses during felling and extraction.

As indicated in the table, total timber loss was about 8.2% with the two major causes, split stems and undiscovered decay, accounting for about 90% of the loss. Similar results on losses associated with conventional logging in Brazil were reported by Winkler (1997), with 8.5% losses at a study site in the central Amazon, and by Gerwing et al. (1996), with losses of 1.7 m³/ha, in the eastern Amazon. Losses in those studies were attributed mainly to poor felling and bucking practices. Once again this emphasises the importance of proper felling technique, which can only be achieved through training and supervision.

6.4 Qualitative assessment of environmental impacts

As mentioned earlier, weather and time constraints limited the investigation of environmental impacts to an assessment of soil disturbance associated with ground-skidding operations in Subplot BL14/VFP.

Survey of skidtrails

The complete skidtrail system in Subplot BL14/VFP was mapped after timber extraction had been completed. Only primary skidtrails are included in the pre-harvest plan (Figure 8a) but the assessment included secondary skidtrails as well (Figure 8b). The width of the skidtrail and degree of soil disturbance were recorded at significant points along each skidtrail.



Figure 8. (a) Left: Primary skidtrail shown in the set-up plan (compare with Figure 4). (b) Right: Actual skidtrail network after timber extraction was completed. Note that the two images are drawn at slightly different scales, and the image at right has been drawn to a higher standard of accuracy so that the roads appear in a different location.

The features of the skidtrail network surveyed after timber extraction had been completed in Subplot BL14/VFP are summarised in Table 13.

Table 13. Skidtrail network in Subplot BL14/VFP.

The area occupied by skidtrails amounts to roughly 5% of the total area of Subplot BL14/VFP. As a point of comparison, Moura-Costa (1997) found that 30-40% of logged areas were typically disturbed by bulldozers in conventional logging in Sabah, Malaysia. During this study, the tractor operator generally retraced the route to the landing that was used to arrive at the felling site. In addition, the volume harvested per hectare was much lower than in the area studied by Moura-Costa.

As noted earlier, primary skidtrails must be planned in advance, marked in the field, and finally approved through the acceptance of the set-up plan by the PNGFA project supervisor. In this case, however, only 8% of the primary skidtrails actually met this requirement. This failure may be attributed to the fact that tree location maps were not prepared prior to preparation of the set-up plan (Figures 4 and 8a). Without the site-specific information provided by such maps it is clearly not possible to accurately plan the primary skidtrails in advance.



Photo 20. Soil disturbance can be quite substantial if weather conditions suddenly deteriorate while skidding operations are underway.

Visual classification of soil disturbance and measurement of the depth of ruts caused by skidding equipment were assessed at significant points such as skidtrail intersections or at regular 30-m intervals along the skidtrails. For the most part, the observed skidtrails were classified in soil disturbance class I. This class is characterised by unexposed or only slightly exposed mineral soil. Soil disturbance class II, characterised by mineral soil partly or fully exposed and often in combination with gullying, was relatively rare on the study area.

Nevertheless, deep ruts can form rapidly when the soils are wet (Photo 20). On about 20% of the 140 measurement points taken in the study area, ruts were found that had depths between 10 and 20 cm. Deeper ruts (20-30 cm) were found on 7.1% of the sample points and the deepest ruts (30-40 cm), on 0.7% of sample points. On the remaining sample points, the depth of tractor tracks was less than 10 cm.