Operational trial of the Selection cut using the 123 method at Northern Pulp Nova Scotia Corporation

Transcription

1 570, boul. Saint-Jean Pointe-Claire, QC H9R 3J9 Operational trial of the Selection cut using the 123 method at Northern Pulp Nova Scotia Corporation By Philippe Meek, Jean A. Plamondon and Peter S. Hamilton February 2011

2 Introduction In many circumstances, companies are finding the social license to conduct forest harvesting operations depends on their capabilities to avoid clearcutting either on their own initiative, or when required. Over the past several years FPInnovations Harvesting Operations researchers have worked to develop an adaptable approach to partial cutting operations that allows forest managers to meet sophisticated silvicultural objectives at a reasonable cost. Among them, the selection cut using the 123 method was developed to provide for harvesting operations that address the concept of perpetual forest cover. It satisfies the principles of unevenaged management by addressing 3 basic silvicultural functions, harvesting, tending and regeneration, in one single operation. Applications of the 123 selection cut method in softwood forests have been demonstrated to be capable of meeting wildlife habitat concerns, maintaining visual quality of high valued viewscapes. As such the method provides alternatives in ecosystem-based management schemes and at the same time can be readily implemented at the operations level. As part of the FPInnovations Hardwood Initiative (improving hardwood sector competitiveness program), the project aims at providing alternative management tools when stand conditions fall outside traditional silviculture criteria for implementing a selection cut. FPInnovations collaborated with Northern Pulp Nova Scotia Corporation to implement a selection cut using the 123 method as developed by FPInnovations. A predominately sugar maple stand, located nearby Economy (NS), was selected to conduct a test trial of the 123 selection cut method. The main goals of this trial were to test the capacity of the tree selection procedure to meet the stand improvement guidelines, and to assess the cost effectiveness of the treatment within Northern Pulp stand conditions. It should be noted that previous trials conducted since August 2009, in other stand conditions have shown that this method is effective in maintaining acceptable harvesting costs, producing operationally feasible ratios of pulp to sawlog, and resulting in silviculturally acceptable growing conditions within the residual stand. Pre and post treatment observations confirm that tree removal can be controlled and that the treatment effectively results in a uniform cover at the stand level. Page 1 RI-2008-

3 Selection cut using the 123 method Successful maintenance of an uneven aged stand requires that management treatments satisfy three main criteria a) the harvest of mature trees, b) the treatment provides crown release for residual intermediate trees, allowing for accelerated growth and c) provide suitable conditions for the regeneration of shade tolerant or semi tolerant t species within a portion of the stand. The 123 method has been developed with the objective of allowing forest operations to economically attain these goals. The 123 partial cut method will support 4 interventions throughout the stands rotation, maintaining canopy coverage throughout the treatment period. These interventions occur at 20 or 30- year intervals (depending on target products, species and growth rate) resulting in many layers of regeneration which develop because the stand canopy is only partial opened, and closes slowly. The 123 method can be implemented easily with conventional harvesting equipment and thus does not require additional capital investment. It takes advantage of the regeneration that develops within the forwarder trails and of the crown release of the trees bordering these trails. Figure 1 illustrates an example of the adapted trail network for the 123 selection cut method. About 33 % of the stand is removed over 50 % of the area. The combined 15 meter wide treatment zone is comprised of a 5-mthe selection process is made at a wide trail, and two adjacent 5-m-widremoval rate of 50 %. Trail width is always of concern and difficult to maintain when using large partial-cut strips, over which machines. The concept of a gate system has been developed which is intrinsic to the 123 system in that it is a guide to the machine operator and ensures success in protecting the residual stand. These gates are simply mature trees left on each side of the trail at regular intervals to control the overall trail width. 5m 5m 5m 5m 5m 5m 5m 5m 5m 5m 5m 5m Page 2

4 Figure 1: Proposed adapted 123 single tree selection harvesting method Figure 2 illustrates how the 123 method was developed to allow 4 passes during the rotation. After the first pass, regeneration is expected to develop in the clearcut forwarder trails and in the adjacent partial cut areas wherever sufficiently improved light conditions permit. The second pass employing the same pattern (5m clearcut trail 5m partial partial-cut cut on either side) will work within the original untreated forest region, leaving regeneration regen established after the first pass untouched. With each entry the he 50% removal zones are treated according to selection guidelines established from the pretreatment stand inventory. Figure 2. Example of adapted selection cut method where trail and partial removal zone locations are shown for the 4 entries per rotation. Page 3

5 Stand description, prescription and effects on stand structure The treated stand was primarily composed of sugar maple with a minor yellow birch component and scattered occurrences of spruce. The pre-treatment conditions are describedd in table 1 and represent data collected from 9 temporary plots randomly distributed within the treatment area. The prevolume, to evaluate the treatment sampling procedure serves to estimate the potential harvestable suitability of the stand for 123 method selection cutting which then lead to defining the tree selection (cutting) guidelines. Tree vigor is always a primary criterion when considering the application of a selection cut and the 123 method is no different. Without sufficient tree vigor, expected response on residual trees will not be obtained. During the pre-treatment sampling, each tree is evaluated on the basis of species, DBH and vigor. The proposed classification requires that the supervisor or harvest planners and the machine operators use the same criteria when describing trees. The operational classification used during this trial has 3 classes: Q1 : a tree with no noticeable defects. Q2 : a tree with a noticeable defect on 1 or 2 faces of the trunk. Q3 : a tree with a noticeable defect on 3 or more faces, and or of an inappropriate species. Defining noticeable defects to account for local conditions and market tolerances should be done prior to implementation of the 123 method. For the present trial, defect identification was confined to the lowest 6 m of the stem, defects were defined as fork, canker, curve, new or old damage, etc. As can be seen in table 1, the stand contains nearly 460 stems per ha with a size class (dbh) distributions typical of the uneven aged stand structure. Additionally sufficient vigor was identified within the smaller diameter classes to expect a desirable response from this size class. This established the validity of applying a selection cut harvest method, easily adapted to the 123-method by concentrating harvest efforts on removing big trees and of non-vigorous mid-sized trees from within the partial cut zone. This allows the vigorous small and mid-sized trees to develop at an accelerated rate. According to the removal distribution proposed in figure 2, the clearcut trail network represents a15 % removal at the stand level, and the removal in the selection zones would be targeted at 50 %. The tree selection guidelines were established to achieve this removal. The operator Page 4

6 was asked to cut all the large trees and half of the mid-sized ( /2= 8 m²/ha) in the selection zone. The weighted removal would be 32 % or 35 m³/ha and could be used for all planning purposes. The operator was given instructions to select non-vigorous trees among the mid-sized in order to improve the quality of the growing stock. This should result in an increase in the percentage of vigorous trees (Q1). Table 1. Pre treatment Stand Inventory. Tree size class all Small Medium Large DBH range (cm) Stand density (stem/ha) Basal area (m²/ha) Merch. volume (m³/ha) Average stem size (m³/stem) Average DBH (cm) Basal area proportion % 27% 32% Quality 1 trees in proportion of basal area 30% 39% 24% 24% Quality 1 trees in proportion of density 41% 46% 22% 31% After felling, but before processing and forwarding, 13 control plots were established within the treated area. The measurementss were conducted in 100 m² plots established within the area treated by selection harvesting. No sampling is conducted in the extraction trails or the untouched areas. The stand statistics are computed from stump diameters using an adjusted volume table (different from pre-treatment sampling using DBH). Post treatment plots which are used to describe the treatments effects, are located only within treated strips, therefore it is not possible to use the same plots as used for pretreatment inventory. All these data were collected during the post-treatment sampling except the pre-treatment percentage of vigorous trees (Q1). Data in table 2 reveal that 180 trees were felled for a volume of 53.6 m³/ha. The average size of trees harvested was 32 % bigger than the standing tree average before treatment. This is one of the major benefits of the selection cut method, from a harvesting economics perspective. The larger trees generally provide a more valuable product basket thus contributing to maintaining the harvest costs closer to those of more conventional harvesting practices. On averagee before treatment, 41 % of the stems received a Q1 rating. After Page 5

7 felling, this proportion increased to 45 % indicating that the operator was able to mostly avoid the harvest of the future crop trees. Only two 5 m-wide strips were treated according to the selection guidelines. In those strips the proportion of Q1 increased to 60 %, demonstrating the stand improvement aspect of the selection cut method. It is important to note thatt this level of improvement was achieved by an operator during his first application of the cutting rules, and without any quality targets. The 123 method has been designed to provide the machine operator with simple, concise, non contradictory rules that can be applied from what the operator sees from his seat. During the current trials, no quality increase goal was set, but this could easily be integrated into the quality monitoring procedure. Table 2. Results from the control plots established after treatments. Pre Post Harvested Difference Density Volume Avg vol. stems/ha m³/ha m³/ /stem % -33% -10% Proportion Q1 % stems/ha 41%* 45% 34% * as shown in table % The 13 post-treatment control plots also provided important operational information: The average trail width was 5.0m, none exceeding 6m. The average trail spacing was 30.8m with 85% of the measurements between 26 and 34m. 80% of the big trees (DBH 40cm) were felled in the selection zones (as requested). 38 % of the mid-sized (22cm < DBH < 40cm) trees were felled in the selection zones (target = 50 %). The control procedure indicates that the desired trail spacing was achieved when the trails were flagged, and that the operator was able to reach the targeted removal rate without having to do all of the prescribed felling. This suggest that the supervisor could rapidly adjust the cutting guidelines to prevent any excessive removal, or if he considers the effect marginal, to monitor over a longer period of time to warrant cutting rule adjustment. Page 6

8 Productivity and cost The harvesting system implementing the 123 selection cut method in this trial was a 3 machine cut- and a forwarder. The to-length team, comprised of a feller-buncher, a butt-plate equipped processor following section describes the machine operations, and presents results of the timing studies. Felling Table 3 summarizes the data collected during observation of the Tigercat 860C feller-buncher (figure 3) in both clearcut and selection cut harvesting. The productivity was good for both treatments indicating that the operator was quick to pick-up the rules of the 123 selection cut. The 11% and 15% drop in stem and volume productivities respectively are largely explained by the increase in moving time associated with a selection cut harvest, where a greater area must be covered to achieve the same harvested wood volume. The operator s need for a clear line of sight when making tree selection decisions increased the amount of time spent brushing. The averagee stem harvested was smaller by 4 % in the selection cut mostly due to a lower presence of large softwood on the selection block. Volumes were estimated from an adapted tree length scale and are gross volumes, and make no assessment or differentiation with respect to relative wood quality. It should be noted that many of the big and uglies left standing during the clearcutting of the trail were cut during the selection portion of the harvest. The calculated 18% felling cost increase is of the same order as observed in other case studies. Page 7

9 Table 3. Productivity and cost for the Feller-buncher Tigercat 860C. Key study results Clearcut Study duration (PMH) 2.1 Average harvested volume (m³/stem) Trees/PMH 202 m³/pmh 62.6 Direct operating cost ($/PMH) 120 Felling cost ($/m³) 1.92 Selection Difference % % % % Work cycle elements Move Brush Cut Move to bunch Arrange logs Bunch Operational delays Total % % % % Figure 3. The Tigercat 860C feller-buncher in a 123 selection cut. Page 8

10 Figure 4. The Hornet processor head on a Tigercat carrier. Processing Table 4 presents the results of the time study of the Hornet processor mounted on a Tigercat carrier (figure 4). The observed productivity of 15 m³/pmh is considerably lower than what would be expected in this size of wood, on a clearcut operation. This can be explained in part by the effort of the operator to maximize fiber recovery. It was observed that beyond a certain point incremental manipulation yielded insufficient volume to warrant the effort. This could easily be corrected should the 123 method be implemented operationally. Another factor was that maneuvering the cumbersome butt-plate processing head and machine tail swing combination within the trail without damaging adjacent residuals or gate trees required noticeable care. While in time, the operator will become more proficient in negotiating/establishing the gates, it does not change the fact that the physical dimensions of the Hornet head pose a longer term problem. In an attempt to alleviate operating limitations of the Hornet an alternate pattern, hereinafter called half-moon, employing some clearcutting within the selection zone was tried briefly before the trial ended. It did appear to reduce some of the difficulties related to maneuvering of the processing head. It must be cautioned though, as this change represents a different management approach more in line with shelterwood Page 9

11 (even-aged) than selection (uneven-aged) management. Overall, the observed $8.61/m³ processing cost can be expected to decrease as operators become more proficient, however this type of head will likely be a limiting factor to further improvements. While the processor was not observed in a clearcut operation during this trial, the half-moon can serve as a benchmark. After adjustments for the larger tree size based on FPInnovations studies we estimate the processing cost in clearcutting would be 4.36 $/m³. Table 4. Productivity and cost for the processor. Key study results Selection Study duration (PMH) 2.5 Average log volume (m3) Average harvested treee volume m3) Trees/PMH 47.7 m3/pmh 15.1 Direct operating cost ($ $/PMH) Felling and processing cost ($/m3) 8.61 Half-moon Work cycle elements Move Load Arrange pile Process Operational delays Total % % 28% 0% 51% 7% 100% Forwarding The Rottne Rapid 8WD forwarder (figure 5) was observed for only a few cycles, and the loads were mostly incomplete (4 to 7 m³). Highlights of the time study are presented in table 5. The productivity was 19.8 m³/pmh for an estimated cost of 6.67 $/m³. Although imperfect because of excess forwarding capacity, this probably remains a fair estimate. As longer forwarding distances would increase cycle times, operators would naturally adjust and ensure full capacity loads. Page 10

12 Table 5. Productivity and cost for the forwarder. Key study results Trips Study duration(pmh) Average Volume(m³/log) Average Volume per cycle Selection Productivity Costing ($/PMH) Costing ($/unit) (m³/pmh) Average distance (m) 100 Work cycle elements % Travel empty 12 Maneuver 2 Load 38 Move during loading 22 Travel loaded 4 Unload 20 Operational delays 2 Total 100 Figure 5. The Rottne Rapid shortwood forwarder. Page 11

13 Total harvesting cost In Table 6 individual machine productivity and direct costs are summarized indicating a total direct cost of $19.30/m³ (including the contractor profit margin) when conducting selection harvesting with the 123 method. It should be recognized these costs represent the cost during the implementation period of the new method. While this number can be used for planning purposes if needed, one would expect cost to decrease as operator familiarity with, and customization of the harvest evolved. Not all harvesting phases were observed in a clear cutting operation, and while we are confident in the following estimates we also suggest that comparison should be carefully interpreted. Using costs generated from observations of the felling ($1.92/m 3 )and forwarding phase($5.67/m³), and estimates for the processing ($4.36/m³) we estimate the cost difference between clearcutting and 123 Selection method would be in the magnitude of $7/m³. This hypothetical difference is important and assumes a similar average harvested tree size for both clearcutting and selection harvest, which is counter to all experience. A more realistic assumption would be to expect the average harvested tree size in the clearcut to be smaller than that of the selection harvest, reducing the cost gap between the treatments. Additionally if this method were to be adopted one would want to give serious consideration to employing an alternate processing technology. Table 6. Productivity and cost related to partial cut treatment Operation m³/pmh $/m³ Feller-buncher 52.9 Processor at the stump 15.1 Forwarder % other contractor cost, risk and profits Total Page 12

14 Conclusions The 123 selection harvesting method has been designed with the knowledge that complex decision making processes for textbook tree selection, while feasible on paper, cannot be implemented in the field by production-oriented machine operators. With this in mind, a key benefit of the 123 method is its operator friendliness. This trial has demonstrated that a basic set of rules can be understood and successfully implemented by a feller-buncher operator in a very short period. Additionally while meeting the demands of the silviculturalist, the general public also finds reason to appreciate the treatment result, in its form of a favorable viewscape. The cost difference that can be expected should be in part bridged through operation proficiency and higher average harvested stem volume in the selection cut. The use of a dangle-head processor would go a long way in increasing productivity/reducing overall costs. Page 13