CASE STUDY: Using Partial Cutting to Reduce Susceptibility of Mature Lodgepole Pine Stands to Mountain Pine Beetle Attack-Beetle Proofing
Extension Note 039 (Revised)
In 1992, researchers from the Canadian Forest Service (CFS), in partnership with Crestbrook Forest Industries Ltd. (CFI), Galloway Lumber Company Ltd., the British Columbia Forest Service, and the Forest Engineering Research Institute of Canada (FERIC), began intensive study of partial cutting and fertilization in Age Class 5 lodgepole pine on three sites in the East Kootenays region of southeastern British Columbia (BC) (Whitehead 1997). One objective of the treatments is to decrease stand susceptibility to epidemic attack by mountain pine beetle. This is often called beetle proofing.
One of the research installations was located on Tree Farm License (TFL) 14 in the Invermere Forest District. CFI and District staffs have since adapted the research prescriptions to suit operational requirements on the TFL, and have developed a workable system at all phases from planning to reforestation. This Extension Note describes beetle proofing in general, and the specific approach taken on TFL 14, where more than 600 ha have been treated (Figure 1).
Beetle proofing is a thinning from below in previously unmanaged mature lodgepole pine to create a more open and uniformly spaced stand. The objective is to improve vigour of individual trees and to alter stand microclimate by increasing temperature, light intensity, and air movement in the clear bole zone. Research suggests that a combination of these factors decreases both stand and tree susceptibility to attack by mountain pine beetle (Safranyik et al 1974; Bartos and Amman 1989; McGregor et al 1981; Mitchell et al 1983).
The Forest Practices Code of BC Act sets various restrictions to operational harvesting-such as riparian management and adjacency rules, and Visual Quality Objectives-that make it challenging for a forest planner to meet the landscape-level objectives on a pine-dominated landbase that is at risk for developing mountain pine beetle epidemics. Beetle proofing may allow some mature pine stands to be held in the scheduling queue for 10-20 years (without catastrophic loss caused by mountain pine beetle) where resource management objectives for wildlife habitat or visual quality require maintenance of mature forest cover. During this time, a beetle-proofed stand may accrue some gain in piece size or volume, and regeneration layers may establish under the residual canopy while adjacent openings "green-up". The potential benefits to integrated resource management are apparent, and therefore beetle proofing is coming of age in the East Kootenays.
Figure 1. Panoramic view of TFL 14 after beetle proofing.
TFL 14 is located south of Golden, BC near Parson. The TFL consists of the entire Spillimacheen River basin, including the benchlands adjacent to the Columbia River wetlands, west to the Glacier National Park boundary. The 151 000-ha landbase is comprised of approximately 85 000 ha of productive forest of which 52 000 ha is net operable forest land with an allowable annual cut (AAC) set recently by the Chief Forester at 165 000 m³. Of this landbase, approximately 63% is dense, fire-origin pine leading or pure pine, much of which is Age Class 5 or older and therefore considered highly susceptible to epidemic attack by mountain pine beetle (Shore and Safranyik 1992).
MANAGEMENT OBJECTIVES AND PLANNING
In addition to the usual Management Plan and Forest Development Plan, higher level planning on TFL 14 includes Resource Management Plans (RMP) for the 22 planning cells that define the various landscapes on the TFL. RMPs consist of a textual description of the management objectives, tables describing resources found within each planning cell, and a mapping folio that provides spatial representation of all identified resource values.
The RMP for the Bench North planning cell, where much of the beetle proofing has been carried out on TFL 14, includes the following management objectives:
Stand-level objectives defined in the beetle proofing Silviculture Prescriptions include the diversification of stand attributes while maintaining harvesting options within and adjacent to the stand. Final overstory removal is planned to occur within 10 to 20 years.
The silviculture system prescribed for most beetle proofing situations may be described as commercial thinning, or as a two-pass shelterwood if regeneration objectives are set for the period between harvest entries. Fifty to seventy per cent of the advanced regeneration layer is typically killed or damaged during harvest operations; but, observations on the CFS research sites suggest that height, diameter, and crown development of undamaged stems are all greater than in unthinned blocks 5 years after thinning. These results are consistent with other research studies. CFI has underplanted several beetle proofed stands with Engelmann spruce. Although performance over the first two to three seasons has been disappointing, CFS's measurements of four species underplanted on two sites suggest that growth improves in the third or fourth season after planting.
Stand Selection Criteria
The beetle proofing prescription for TFL 14 uses the following cut-and-leave specifications, which have evolved over the past 4-5 years and are vital to achieving the desired results:
These selection criteria are designed to be clearly understood by logging supervisors and contractors (fallers). They usually result in retention of approximately 400 stems/ha and 50% of the pre-harvest basal area, but are intended to provide enough flexibility to allow for natural inter- and intra-stand variations, and to address worker safety and harvesting efficiency while eliminating costly tree marking.
Block layout must be done with greater consideration for terrain and stand lean as well as for the differing requirements of the mechanized and hand-falling systems described below.
Pre-locating skid trails is desirable to achieve minimum disturbance and residual stem damage, and reasonable tree-to-truck costs. Skid trails are laid out to meet the specific falling requirements of: thinning from below, block-specific terrain conditions, the height and size of the timber, the type of harvesting system being used, and the contractor's own preferences. This phase is best carried out by layout personnel with a harvesting (preferably falling) background, in conjunction with the logging contractor assigned to the block.
Trails are constructed using a combination of a crawler-tractor (on even ground) and a smaller excavator hoe equipped with a hydraulic thumb to push over and bunch the timber along the pre-located trails and to construct any bladed or excavated trails as dictated by the terrain and slopes. Trail construction and related phases can cost between $3.00 and 6.00/m3, depending on the average volume/tree harvested, volume/ha removed, terrain, and soil conditions. This is within the range of trail construction costs for other partial cutting systems, but generally 40-50% higher than for clearcut blocks due to the lower volume/ha removed and somewhat higher trail densities. Figure 2 shows post-harvest results.
Figure 2. Post-harvesting results
The harvesting phase is completed using one of two conventional ground-skidding systems:
Beetle proofing on TFL 14 has been carried out to three inter-tree spacings: 4 m, 5 m, and 6 m. Research results indicate that all these spacings alter stand and tree microclimate in the desired way. The 6-m spacing has been used where significant numbers of advanced regeneration (Layers 2 and 3) are present which provide additional shading and wind flow resistance, i.e. reducing the effective beetle proofing attributes. Operationally, this wider spacing is more efficient and economical to harvest but the risk of windthrow is also high. The 4-m spacing has been applied in heavily stocked stands with smaller average diameters and poorer height:diameter ratios (i.e. where the risks of wind and snow damage are greater), but has not avoided damage in patches where pre-treatment stem densities exceed about 1600-1800 stems/ha.
CFI's planning and harvesting staff were encouraged by the initial success of the CFS research trials; they saw potential for improving management at the landscape level rather than undertaking reactive salvage and control harvesting of stands driven by unpredictable mountain pine beetle cycles.
Over 600 ha of pine have been beetle proofed on TFL 14 over the past several years with varying degrees of success. Many factors contributed to the success:
The result is a clear example of practical adaptive forest management.
Even with most of these elements in place, the beetle-proofing costs (using either harvesting system) are 15 to 40% higher than clearcutting in similar stands. Logging costs can be minimized and worker safety increased by decreasing the skid trail spacing, and increasing the road and landing densities (within acceptable site-disturbance levels). The volume/ha removed, average piece size, and terrain are the most critical factors which affect logging costs (Mitchell 1994). TFL 14 managers consider beetle proofing in stands where the volume removal is under 100 m³/ha, or where the average piece size is 0.2 m³ or less, to be either marginal or uneconomical (the high pulp markets experienced in the early 1990s not withstanding).
In addition, silviculture challenges include residual stem vigour and windfirmness, regeneration performance under partially shaded conditions, and the potential for damage to lower layers during overstory removal.
Also, some benefits of beetle proofing that are more difficult to factor into the decision-making process, including:
While all timber on TFL 14 is hauled tree length on off-highway trucks to the log yard in Parson, beetle proofing is also well suited to cut-to-length systems utilizing harvesters/processors and forwarders. On the down side, with larger areas being harvested by partial cutting, there are increased obligations and risks associated with silviculture, forest health, windthrow, and road maintenance.
Bartos, D.L. and G.D. Amman. 1989. Microclimate: An Alternative to Tree Vigour as a Basis for Mountain Pine Beetle Infestations. Res. Paper INT-400. Intermountain Res. Stn., USDA Forest Service.
McGregor, M.D.; G.D. Amman; R.F. Schmitz; and R.D. Oakes. 1987. "Partial cutting lodgepole pine stands to reduce losses to the mountain pine beetle" in Can. J. For. Res. 17:1234-1239.
Mitchell, J.L. 1994. Commercial Thinning of Mature Lodgepole Pine to Reduce Susceptibility to Mountain Pine Beetle. Special Report SR-94. FERIC, Vancouver, BC.
Mitchell, R.G.; R.H. Waring; and G.B. Pitman. 1983. "Thinning lodgepole pine increases tree vigour and resistance to mountain pine beetle" in For. Sci. 29:204-211.
Safranyik, L.; D.M. Shrimpton; and H.S. Whitney. 1974. Management of Lodgepole Pine to Reduce Losses from the Mountain Pine Beetle. For. Tech. Rep. No. 1. Pacific For. Ctr., Can. For. Service, Victoria, BC.
Shore, T.L. and L. Safranyik. 1992. Susceptibility and Risk Rating Systems for the Mountain Pine Beetle in Lodgepole Pine Stands. Inf. Rep. BC-X-336. Pacific For. Ctr., Can. For. Service, Victoria, BC.
Whitehead, R.J.; L. Safranyik; B.N. Brown; R.A. Benton; T. Shore; and D.A. Linton. 1997. Modifying Silvicultural Systems for Mature Lodgepole Pine: A Research and Operations Partnership-Reducing Stand Susceptibility to Mountain Pine Beetle by Commercial Thinning, Fertilization and Conversion to a Mixed Species Shelterwood-Research Working Plan 1992-2002. File Report P58001-97-01. Pacific For. Ctr., Can. For. Service, Victoria, BC.
|FOR FURTHER INFORMATION, CONTACT:|
Crestbrook Forest Industries Ltd. Parson, BC
|Deb De Long, RPF,
Silviculture Systems Research Forester
Nelson Forest Region, Ministry of Forests Nelson, BC
Forest Health Officer,
Invermere Forest District
Nelson Forest Region, Ministry of Forests Invermere, BC
Pacific Forestry Centre, Canadian Forest Service
Return to Extension Notes Index