Observations of Three Shortwood System Machines in a Hardwood Stand using a Single Selection Cutting Approach with Temporary Trails

Transcription

1 580, boul. Saint-Jean Pointe-Claire, QC H9R 3J9 Observations of Three Shortwood System Machines in a Hardwood Stand using a Single Selection Cutting Approach with Temporary Trails Vincent Roy, F. Eng. December 2009

2 Introduction FPInnovations, Feric division, in collaboration with New Page Corporation, conducted a study of a new single-tree selection cutting method in a hardwood stand. This approach, using temporary trails, could be used as an alternative to group selection cutting. The study s objectives were to verify if this method could improve the quality and vigour of moderate quality hardwood stands, help salvage mature merchantable sawlogs and be performed at a reasonable cost. For the trials, selection cutting with two different trail patterns was compared with group selection. The first one used 30-meter spacing between trails with a 5-meter selection cutting zone on each side of the harvester (Figure 1). The second one used inserts or secondary trails, which allowed the harvester to reach large trees in the 15-metre-wide non-treated zone. This report presents the productivity studies that were done during the trials and describes the effect of treatments on the stand. Figure 1: Single-tree selection method. 5m 5m 5m 15m 5m 5m 5m 15m Page 1 Single selection harvesting

3 Stand description Table 1 presents pre-cruise results for the three treatment blocks. Selection cutblocks were mainly stocked with sugar and red maple although some yellow birch was scattered throughout. Comparing the two cutblocks harvested using the single selection cutting method; the first block had a higher stem density, but a lower average volume per stem. The second block had a larger proportion of very large trees. The group selection block was stocked with sugar and red maple with scattered yellow birch as well. Table 1: Pre-treatment stand description Group Selection Harvesting 1 Harvesting 2 Basal area (m 2 /ha) Density (stems/ha) Standing merchantable volume (m 3 /ha) Average DBH (cm) Average stem volume (m 3 /stem) % AGS (VS tree classes) Prescription The selection was made in the removal zone illustrated in Figure 2. The feller-buncher operator was asked to cut one out of four trees with a DBH larger than 40 cm (16 inches and more) with priority to the poorest quality (unacceptable growing stock (UGS)). If no trees larger than 40 cm were present, the operator was asked to remove 1 out of 4 trees in the mid-size tree range (between 20 and 40 cm), still aiming for the poorest quality first. If no mid-size trees were present, no trees were removed. This prescription was applied in the removal zone allowing good distribution of the selection throughout the whole treatment. This zone was basically the operator s field of vision on either side of the main trail. The final target was to cut around 50% of the volume, while maintaining a basal area between 12 and 16 m²/ha, in the selection zone. This would allow enough light to enter the stand to develop a new cohort of maple regeneration and also allow the acceptable growing stock (AGS) to grow more freely. The next entry into the stand would be in years, when the regeneration is well developed. It will target the 15-metre-wide untouched zone so as to promote a new cohort of regeneration, sawlog Page 2

4 salvage and thinning of the developing mid-sized AGS trees. Figure 2b presents the four entries for the selection cutting with temporary trails. The timing of each entry would consider local growing conditions and stand development. 5 m 15 m Figure 2: Selection zone Figure 2b: Typical sequence for implementation of selection cutting with temporary trails. Page 3

5 Productivity Table 2 shows the results of the productivity study on a block-by-block basis. Terrain conditions were favourable (CPPA ) throughout most of the operating zone. Feller-buncher productivity ranged from 47 to 64 m³/pmh. The Group selection block had the lowest productivity (47 m³/pmh), resulting from the smaller harvested tree size. The estimated direct felling cost was $3.29/m³. In the Single selection 1 block, terrain conditions were also very favourable (CPPA ) in most of the operating zone. Productivity was higher (63.5 m³/pmh) than in the two other blocks. Fellerbuncher productivity was significantly influenced by the larger average volume per stem. With the single selection cutting method, trees over 5 metres zone were not cut. The estimated direct felling cost was $2.44/m³. In the Single selection 2 block, the terrain conditions were also very favourable (CPPA ) in the operating zone. Surprisingly, the average volume of the felled trees was comparable in the two selection cut blocks. Feller-buncher productivity was lower than in block 1. Fewer stems per PMH were harvested in the single selection 2 block. The time distribution for the working cycle elements shows that travelling time was longer when inserts were used to take trees away from the trail. The estimated direct felling cost was $2.63/m³. Comparing the feller-buncher productivity of the two selection cuts was easy because the average tree size was the same. When there were no inserts, productivity was 7% higher. The time spent to select and get to the selected trees was time consuming. The trees in question were large, therefore sustaining productivity. The high productivity achieved with the inserts can give a clear advantage to this method when stand conditions are favourable. During the trial, productivity was 115 m³/pmh in the inserts alone, due to the 0.9 m³ per harvested tree. Elsewhere, the trees harvested from the trail and the 5-metre selection zones were smaller. A fair productivity comparison between the group selection with the two other treatments is feasible if the effect of the smaller stem size is offset. Using a typical Feric productivity curve for hardwood clearcutting, the observed operator was 6% more productive at m³/stem. The group selection method would minimize the difficulties created by residual trees. Referring to this curve at m³/stem, the adjusted productivity would be 54 m³/pmh. It is still lower than the productivity observed in the two single selection cutblocks. It shows clearly that cost reduction is not only linked to tree size. Page 4

6 The detailed timing shows that the work cycle is very similar for all treatments. Moving the machine from one group selection to the next one is time consuming. Bunching the trees to facilitate loading by the processor is not an easy task when the tree removal rate is high especially in group selection. Table 2: Productivity and cost² of the TJ608 feller-buncher Group selection Single selection 1 Single selection 2 Study duration (PMH) Average harvested volume (m³/stem) Productivity Trees/PMH m³/pmh Direct operating cost ($/PMH) Felling cost ($/m³) Productivity estimation 1 (m³/pmh) 54 Relative productivity (%) % 110% Work cycle elements % min/m³ % min/m³ % min/m³ Move 36% % % 0.40 Brush 12% % % 0.09 Cut 23% % % 0.23 Move to bunch 1% % % 0.02 Arrange logs 1% % % 0.01 Bunch 22% % % 0.25 Operational delays 5% % % 0.05 Total 100% % % : Estimation was calculated using FPInnovations Interface equation (allows comparison of treatments at equal harvested volumes). 2 : Excluding transportation and supervision costs, as well as profits and overhead. Costs are based on the purchase price of a new harvester. Page 5

7 Table 3 shows the results of the productivity study for the processor in the group selection block only. Terrain conditions were favourable (CPPA ) throughout the whole operating zone. Processor productivity was m³/pmh for an estimated cost of $7.12/m³. Like most harvesting machines, processor productivity will be influenced by the average volume per stem and types of products. Compared with other Feric studies, the productivity was good. Reasonable efforts were made to extract the maximum fibre in the tops (mainly pulp logs). The processing of short logs, especially pulp length, is time consuming since there are lots of forks and large branches in hardwoods and this has a major effect on productivity. As shown in Table 3, process is the most time-consuming work cycle element. Table 3: Productivity and cost 1 of the Tigercat 753 processor equipped with a Logmax 7000 head Group selection Study duration (PMH) 2.4 Average processed volume (m³/log) Average processed volume (m³/tree) Productivity Trees/PMH 69 m³/pmh 20.4 Direct operating cost ($/PMH) Processing cost ($/m³) 7.11 Work cycle elements % min/m³ Move 9% 0.26 Load 22% 0.65 Arrange pile 4% 0.13 Process 58% 1.71 Operational delays 7% 0.20 Total 100% : Excluding transportation and supervision costs, as well as profits and overhead. Costs are based on the purchase price of a new harvester. Table 4 shows the results of the productivity study for the forwarder in the group selection block. Terrain conditions were favourable (CPPA ) throughout the whole operating zone. Forwarder productivity was 16.1 m³/pmh for an estimated cost of $9.00/m³. Those numbers are comparable with previous Feric studies. Though we weren t able to study the forwarder in the single selection cutblocks, it would have been interesting to do so. In the group selection, logs were concentrated in larger piles then they would have been in the single selection method. This can lead to a reduction in productivity of up to 15%, but this was previously observed in a softwood operation. Page 6

8 Table 4: Productivity and cost 1 of the Prentice 2548 forwarder Average skidding distance of 150 m Group Selection Trips 4 Study duration (PMH) 2.4 Average volume (m³/log) Average volume per trip (m³) 9.6 Productivity (logs/pmh) 225 (m³/pmh) 16.1 Direct operating cost ($/PMH) Forwarding cost ($/m³) 9.00 Work cycle elements % min/m³ Travel empty 20% 0.73 Manoeuvres 0% 0.00 Load 32% 1.19 Move loaded 7% 0.26 Travel loaded 19% 0.71 Unload 21% 0.80 Operational delays 1% 0.03 Total 100% : Excluding transportation and supervision costs, as well as profits and overhead. Costs are based on the purchase price of a new harvester. Post treatment Table 5 shows the post-cruise data collected from the first single selection cutblock. Plots were 100 m² (5 x 20) and made in the 5-metre-wide thinned strip. The prescription focused on harvesting large trees of up to approximately 30% of stand density and close to 50% of stand volume. The first part of the table shows the conformity. It shows that the operator was able to select one out of three trees (27%) and that large trees (58% of the volume) were harvested. The second part shows the effect of the treatment on the stand. It shows that 30% of stand density was removed for a 45% total volume removal. Volume harvested came from trails and selection zones. The operator selected large and poor quality trees, and since the average volume decreased and the AGS increased. While selecting the trees, the operator was asked to keep 30-metre spacing between the 5-metre-wide trails. Even if the GPS unit Page 7

9 was not working in the feller-buncher and no flags were used, the average spacing for the whole block was 31.6 m and the average trail width was 5.3 m. Table 5: Single selection 1 stand and selection zone description 1 30 m Density Volume Average volume AGS stems/ha m³/ha m³/stem % Selection zone description Before % After % Harvested Difference -27% -58% -42% 13% Stand description Before % After % Harvested Difference -30% -45% -21% 13% 1: The volume table used might over-estimate. Page 8

10 Table 6 shows post-cruise results for the single selection 2 with inserts. The results were expected to be similar to those from the first single selection cutting. Again the selection rule was well applied. The first part of the table shows that the operator was able to pick close to one out of three trees (23%) and harvest large trees (57%). The second part shows that 37% of stand density was removed for a 42% total volume removal. The operator selected large and poor quality trees, since the average volume decreased and the AGS increased. While selecting the trees, the operator was asked to keep 30-metre spacing between the 5-metre-wide trails. Even if the GPS unit was not working in the feller-buncher and no flag was used, the average spacing for the whole block was 31.2 m and the average trail width was 5.1 m. Table 6: Single selection 2 stand and selection zone description 1 Inserts Density Volume Average volume AGS stems/ha m³/ha m³/stem % Selection zone description Before % After % Harvested Difference -23% -57% -44% 20% Stand description Before % After % Harvested Difference -27% -42% -21% 20% 1: The volume table used might over-estimate Page 9

11 Discussion Table 7 gives the direct costs evaluated during the study. It shows that considering the same costs as the hypotheses in Tables 2 and 3 with a 10% increase in forwarder costs based on previous studies, both single selection cutting costs are comparable, with only $0.14 and $0.31/m³ difference. However, validating these processing and forwarding costs would require a more exhaustive study. Table 7: Direct operationnal costs Group Selection Single selection 1 Single selection 2 Felling cost ($/m³) Processing cost ($/m³)* Forwarding cost ($/m³) Total ($/m³) Difference ($/m³) *: Same volume per stem processed for the same direct cost estimation This study showed that using a single selection method can improve the cost of the operation mainly during felling. Even if it was a short duration study, implementation standards were achieved with the feller-buncher operator. The operator was able to follow the prescription and harvest large and poor quality trees within the selection zone. The productivity of the feller-buncher could improve as the operator gains experience. A GPS unit would also facilitate the operator s work. The single selection harvesting method using inserts will work best for mid to poor quality stands with a good proportion of large trees. Using inserts allows the feller-buncher to cut trees that would not survive until the next rotation. Using both single selection harvesting methods can improve stand quality and crown release. The prescription used in the selection zone could be somewhat flexible. For instance, the prescription could aim for quality control, species control, or light and opening management. By defining silvicultural objectives prior to the operation, the prescription can be more refined and address more specific concerns. Thus, to more refined it is the higher the cost will be. Page 10