optimizing the combined harvesting and road ...

2003 Council on Forest Engineering (COFE) Conference Proceedings: “Forest Operations Among Competing Forest Uses” Bar Harbor, September 7-10, 2003

OPTIMIZING THE COMBINED HARVESTING AND ROAD CONSTRUCTION COSTS FOR A DISPERSED HARVESTING REGIME Luc LeBel, François R. Nadeau, Osvaldo Valeria Université Laval, Faculté de Foresterie et Géomatique. Québec, Canada, G1K 7P4 [email protected] INTRODUCTION Planning for forest harvesting is based on two principal elements: road construction and the selection of cutover areas. Moreover, these elements represent the most significant timber harvesting costs. Forest planners can already use proven analytical tools to take these aspects into account when planning operations. Among these, the optimal road spacing model, which minimizes the combined road/forwarding cost, determines the size of the road network needed to provide access to an area (Matthews 1942, Thompson 1992, Plamondon et al. 1994). In recent years, forestry has been at the centre of international discussions about sustainable development. In this regard, to promote the multiple use of forests while maintaining biodiversity, forest managers are reconsidering how to plan interventions in light of new forestry practices. Among these, methods that favour the distribution of cutovers over an area are likely to result in increased costs associated with establishing and maintaining the road network (Ketcheson 1982, Gingras 1997, Favreau et al. 2000, Nadeau 2002). According to the road spacing model, fibre supply costs can be minimized by optimizing the forwarding distance. It therefore seems necessary to review current forwarding practices in order to include the possible consequences of the choice of cutover distribution in the cost of the road network. The analysis of a combined cost model was done to determine the effects of a dispersed harvest scenario on the forwarding distance and road construction costs. Determination of the combined cost The model used to calculate the combined road/forwarding cost was presented for the first time by Matthews (1942). This simplistic model is only valid for haul roads and presumes they are parallel and uniformly spaced. The equation that expresses the combined road/forwarding cost in relation to the forwarding distance is obtained by adding the cost of the forwarding function to the unit cost for road construction. The primary derivative of this function will determine the optimum distance that will minimize the combined cost. Cutover dispersal and effect on the road network Dispersing cutovers means that a larger territory must be accessed to harvest a given volume. Thus, because the distance between cutting blocks is greater, road construction must be accelerated during the initial years after implementing this system (Ketcheson 1982, Nelson et al. 1991, Hedin 1995). Also, the roads will be used for a longer period and will require maintenance and restoration to support on-going harvesting operations (Nadeau 2002). Consequently, there is a financial impact associated with moving up road construction costs and adding road maintenance and restoration costs.


As noted, dispersing cutover areas has a direct impact on overall road costs. Additional longterm capital and maintenance costs represent a significant financial burden, and must be considered when evaluating road spacing. Also, for strip cuts, Johnson et al. (1987) evaluated that an increase in the forwarding distance from 183 m to 366 m would reduce additional capital road costs by 26%. However, these authors did not integrate the increase in forwarding costs in their analysis; their hypothesis overestimates the true savings. A modification is therefore needed to take into account the true effect of combined road/forwarding costs when carrying out dispersed harvesting. METHODS The approach used was to compare the combined road/forwarding cost of a conventional harvesting scenario to the cost of a dispersed harvesting scenario. Simulations were carried out using the Matthews simplified model (1942), adapted from Plamondon et al. (1994). However, to take the importance of roads into account in a strategy favouring dispersed cutover areas, an adapted version of the model was created (Figure 1). Combined road/forwarding cost : 10    Cope Ccombined ($/m³) = Croads + Cforwarding = AEC  +    2 b ( V ) d 58 . 61 d  0 . 2339    m  i1i m  AEC  Sn n   n 1 1i   (1i)m 1 Mean optimal forwarding distance (dopt): 1

 (10.2339) 1058.61 dopt AEC   2b(V)(0.2339)Cope  List of variables and symbols: d: Mean forwarding distance (m) V: Volume per hectare to harvest (144 m3/ha) b: 1 or 2; forwarding on one or two sides of the road (two sides) Cope : Hourly operating cost of forwarder ($70/pmh) AEC : Equivalent annual road cost ($/km) i: Discount rate (5.8%) Sn : Annual expenditures n: Year (1, 2, 3, ..., m), where m is the analysis horizon

Figure 1. Establishment of the combined road/forwarding cost and the optimal mean forwarding distance adapted from Plamondon et al. (1994). The comparative analysis was done using Montmorency Forest. This 60 km2 territory has been managed for almost 40 years using a dispersed cutover regime. Records of forestry operations expenses for this period go back to 1963, which made it possible to prepare a complete picture of the costs pertaining to the road network (construction, maintenance and restoration).


Forwarding cost The shortwood harvesting system was used for the analysis. Since no local data were available for the operating costs of the shortwood forwarder, the productivity equation in Plamondon et al. (1994) was used for the simulations. The cost of the operation is obtained by applying the hourly equipment rate to the calculated productivity. Road cost The overall road cost of the harvesting network was determined for the two intervention scenarios (conventional and dispersed). For the conventional scenario, the cost includes only the unit cost of construction. For the dispersed scenario, the additional capital and maintenance costs must be absorbed, therefore they are added to the unit cost of construction in order to generate an overall road cost. The cost calculation is done on the basis of the equivalent annual cost (EAC) on a 60-year horizon, which is the rotation period. To express the cost in terms of $/km, the calculated annuity is divided by the mean length of roads that are constructed or maintained annually. At Montmorency Forest, the harvesting road network totals 87.4 km. Consequently, for the analysis horizon, mean annual construction is 1.456 km. Though these values may seem minimal in comparison to industrial operations usually encountered in Quebec, they are little influenced by the scale of the analysis. Road construction Establishment of the harvesting network at Montmorency Forest took 40 years. In comparison, a conventional scenario would have taken 60 years, assuming a constant annual development. At the end of the rotation, since all the wood has been harvested, it is presumed that independent of the scenario, the same road network would have been developed. However, to support the dispersed harvesting regime, more roads must be built at the start of the rotation, causing a desynchronization between road construction and harvest levels in the short term. The effect of the desynchronization comes from having moved construction costs forward. The EAC of road construction for the conventional and dispersed scenarios are $14,165/km and $17,399/km, respectively. Road maintenance Distributing the harvest over time and space makes it necessary to carry out additional maintenance and restoration work to maintain road quality. At Montmorency Forest, additional road maintenance and restoration work results in EACs of $1,097/km and $1,458/km, respectively. It is assumed that the conventional harvesting scenario would not entail these expenses, since the roads are generally used only while harvesting is carried out and are then abandoned until the next rotation. Taking into account the additional costs associated with dispersed cutting areas, combining calculation hypotheses shows that road costs for conventional and dispersed scenarios are $14,165/km and $19,954/km, respectively. Combined road/forwarding cost Given that the road cost for the dispersed scenario is higher than for the conventional scenario, a comparison of the combined costs clearly shows that the optimal forwarding distance for the


dispersed scenario will be higher than for the conventional scenario (Figure 2). The additional capital and maintenance costs increase the minimum combined cost by $0.36/m3, increasing from $5.33/m3 (Point A) to $5.69/m3 (Point C). The mean optimal forwarding distance therefore increases from 243 m to 321 m. 9 8

Zone of optimality

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Mean forwarding distance (m) Forwarding cost Road cost conventional Combined cost conventionnal Road cost dispersed Combine cost dispersed Optimal distance (m)

Figure 2. Comparison of the combined road/forwarding cost for the conventional and dispersed scenarios. If the dispersed harvesting regime is introduced without increasing the forwarding distance, the system will not be optimized and will cost $5.74/m3 (Point B) rather than $5.69/m3 (Point A). Consequently, by increasing the mean forwarding distance it will be possible to reduce the combined cost, since to operate optimally, the forwarding distance in the dispersed scenario must be 321 m (moving from Point B to Point C). In this case, the increased distance will result in reducing the road network density from 2.05 km/km2 to 1.56 km/km2 and the associated road cost by $0.35/m3. On the other hand, the forwarding cost is increased by $0.29/m3. In this way, changing from a forwarding distance of 243 m to 321 m results in a reduction in the combined road/forwarding cost of $0.05/m3, or 1 percent of the total cost. Analysis of results


When introducing the dispersed harvesting regime, the choice of a cutting pattern that will maximize the volume harvested per kilometre of road is of great importance, since it will directly influence the additional need for roads. Also, the maintenance costs will have a significant effect. Because the additional cost is borne by the dispersed scenario, a variation in the costs incurred will have a direct impact on the cost differential. At the other extreme, the road cost and the capital cost will result in little variation, since they affect the two scenarios in an equivalent proportion. Finally, another factor to consider is the choice of harvesting system, and therefore the type of forwarding equipment to use. Notwithstanding these factors, for this analysis it was assumed that the conventional scenario was already operating at its optimal forwarding distance. In this regard, the behaviour of the combined cost function near its optimum is only slightly sensitive to a variation in the distance. It is therefore not surprising that there is such a low potential to reduce costs. However, if the conventional scenario had operated at a shorter than its optimum distance, the situation would have been different. For example, if the mean distance for the conventional scenario had been 150 m, the potential for reducing the cost would have been $0.48/m3. Consequently, operating at a shorter distance than the system’s optimum is more costly than is operating at a greater-thanoptimum distance. DISCUSSION In the case of the Montmorency Forest, reducing the combined cost by using optimum spacing results in an annual gain of $720 (annual volume harvested: 12,000 m3). Objectively, though the reduction is small, increasing the mean forwarding distance results in a net reduction of the combined cost and reduces the increase in road costs entailed by the dispersed cutting regime. However, when the implications of such an increase are taken into account, the potential gain is perhaps only illusory. For example, it is probable that an increase in the forwarding distance results in an increase in the frequency and severity of rutting. Moreover, because space to pile wood at roadside is limited, it is possible that operations could be complicated by such a measure, since increasing the depth of cutover blocks will increase the volume of wood delivered to roadside. Finally, it is not certain that the terrain will allow the operations manager to establish a wider-spaced road network. Hilly terrain and a complex drainage system will limit the possibility of increasing the forwarding distance. It is probable that in some regions, such an increase is impossible. Yet, any reduction in road density must be considered with great attention since the lost of productive area has become a major concern in several jurisdictions. CONCLUSION This analysis confirms that the optimal forwarding distance for a dispersed harvesting regime is greater than for a conventional regime. The increase is attributed to additional capital and road maintenance costs, factors that were adapted to Matthews’ model. The calculation hypotheses used at the Montmorency Forest suggest that increasing the forwarding distance reduces the combined road/forwarding cost by 1 percent for a dispersed harvesting regime. However, though the analysis suggests that a reduction of the cost is possible, other factors must be taken into consideration.


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