Bark Beetle Guidebook: Chapter3b

[Bark Beetle Management Guidebook Table of Contents]

Spruce beetle

Hazard rating

Hazard rating identifies those stands where substantial losses can be expected to occur if an outbreak of spruce beetle occurs. This valuable planting tool identifies those stands that are highly susceptible to attack. Once all spruce stands in an area have been rated, resources can be directed toward those stands with the highest hazard so that losses can be minimized. Hazard rating considers stand age, host basal area, stand density, and elevation.

Stand susceptibility

High hazard stands have:

an average spruce dbh greater than or equal to 41 cm
a spruce volume exceeding 300 m³ /ha
more than 65% spruce in well-drained creek bottoms.

In general, the order of hazard for spruce stands is:

stands in creek bottoms
better stands of spruce on benches, slopes, and high ridges
poorer stands on benches, slopes, and high ridges
mixtures of spruce and lodgepole pine
stands containing all immature spruce.

To determine stand hazard, sum the relative weights depicted in Table 11. Stands with a higher rating will sustain greater damage from spruce beetle attack than a stand with a lower rating. The ratings are qualitative, not quantitative. Some biogeoclimatic zones (BGCZ) do not occur in all regions of the province and ratings may vary.

Table 11. Values for factors used to derive spruce beetle stand hazard rating

Hazard ratings can be used to set priorities for surveys and treatments and may be used during the preparation of forest development plans as a tool in preventive management.

Risk rating

Stand risk is the probability that the stand will be attacked or reattacked based on the proximity and incidence of a spruce beetle infestation. If the stand is not currently infested, it may be attacked by spruce beetle adults immigrating from adjacent infested stands. Any susceptible stand within 2 km of a spruce beetle infestation would be at high risk. Stands with high hazard and risk values have a high priority for management.

Ground detection

Spruce beetle infestations located from aerial surveys or other sources are surveyed using a two-stage system. The first survey, the walkthrough, is a “coarse filter” that quickly determines the extent of the infestation and the options that are available based on the sanitation harvest index thresholds described below. Probes are used to gather more precise information to clarify management alternatives. A treatment decision is then developed for the stand based on the intensity of infestation, the beetle life cycle, and other management considerations.

Walkthroughs are non-systematic preliminary ground reconnaissance surveys conducted to estimate:

the size and spatial distribution of the infestation

the incidence and severity of the infestation as measured by:
– % of spruce attacked in the last three years
– attack densities and success
– vigour of new broods as measured by random bark samples

access, operability, and integrated resource management issues

sanitation harvest index

the necessity to obtain further information or take other action as detailed below (Table 12).

The configuration and extent of walkthroughs are site-specific decisions made by the surveyor. Surveyors should conduct their walkthrough and then attempt to select a representative portion of the area to collect 100–200 m of probe data. Regardless of the walkthrough technique, the surveyor will classify the area/stand by calculating a sanitation harvest index using the data described below. If the sanitation harvest index is between 600 and 999, a grid probe is required to more accurately classify the infestation (Table 12).

The stand hazard index is used to rank the sanitation/salvage harvesting priorities for stands attacked by spruce beetle. Larger numbers indicate a higher priority for sanitation harvesting. Note that the salvage component also includes older attacks. This portion of the formula may be deleted if the salvage component is unmillable (e.g., for plywood).

The sanitation harvest index is calculated as follows:

Sanitation harvest index = (A + B + C) x D

where:

A = % most recent attack in stand

B = % 1-year-old attack in stand/1.5

C = % 2-year-old attack in stand/2.0

D = total % of healthy and attacked spruce in stand.

Table 12. Recommendations for further action based on walkthrough estimates

Probes are systematic and detailed secondary ground reconnaissance surveys. Probing will determine detailed, more precise estimates of the same information gathered from walkthroughs, and will provide sufficient information to stratify the area for various management actions. If probing is recommended, delineated stands should be probed via systematic parallel probe lines as follows:

survey lines are spaced at 100 m intervals
probe lines (strips) are 10 m wide (5 m on each side of centre line)
strips are continuous and extend at least 100 m past the last infested trees
all trees greater than or equal to 17.5 cm dbh within the 10 m wide strip will be recorded within one of the existing diameter classes
information will be summarized in 100 m units, so all lines should be in multiples of 100 m
features pertinent to harvesting, such as creeks, roads, marshes, and cutblock openings should be noted.

All spruce beetle-attacked trees will be recorded by attack codes 1–6 as summarized in Table 13. Probers must remove at least a small portion of phloem from every infested tree within their 10 m strip to ensure coding accuracy. All attacked trees must also be mapped.

Table 13. Spruce beetle attack codes

Cruising is conducted to assess the merchantability and value of timber prior to harvesting. Although spruce beetle impact can be determined from a cruise, cruises are: 1) not detailed enough, 2) not designed to record beetle severity and multiple-year attacks, and 3) are seldom conducted by sufficiently experienced beetle classifiers. Therefore, probing should not be conducted in conjunction with cruising, nor should cruising precede a walkthrough or probe.

Management options

Strategies for spruce beetle are similar to those for mountain pine beetle and other bark beetles.

Selection and application of management strategies

Choice of management strategies for spruce beetle will depend on:

the size and pattern of the infestation
the severity of the attack in each of the last three years
the vigour and survival of the new broods
the stand hazard
integrated resource management issues/constraints
existing and future access
harvesting operability.

Selection of the most appropriate course of action is illustrated in Figure 5.

Figure 5. Selection of management actions for spruce beetle.

Treatment options

Some of the treatments for spruce beetle differ from other bark beetles and timing of activities differ due to variations in the life cycle. Timing of management activities for spruce beetle is given in Table 14. After detection, treatment options are limited to three general tactics:

harvesting
trap trees (conventional and lethal)
prevention (including hauling restrictions).

Harvesting

A. Sanitation harvesting for spruce beetle suppression maximizes the extraction of currently infested spruce stands in order to reduce the existing population and to prevent their spread. The highest priority is given to stands with high levels of new attack, high hazard, and a high risk of spread. All harvesting methods can be used.

B. Salvage harvesting recovers most spruce that were attacked by spruce beetle and such trees no longer have any living broods. Salvage harvesting is primarily conducted to recover damaged timber before it loses its value for potential wood products. This tactic does not reduce spruce beetle populations, but is the first step in returning the site to forest production.

Table 14. Recommended management activity time table for spruce beetle

Applicable harvesting systems

Clearcut harvesting is normally the most effective and cost-efficient control strategy for extracting large aggregations of infested spruce. Maximum cutblock size must not exceed 60 ha for the central and northern interior and 40 ha in southern B.C. unless the cutblock incorporates characteristics of natural disturbance (reserves).
Partial harvesting systems: sanitation harvesting is an uneven-aged silvicultural system in which infested patches of spruce are removed, creating small openings which are usually no larger than twice the height of mature spruce. The objective is to extract as much infested spruce as possible but still leave a mosaic of various aged groups of trees. Careful planning, layout, harvesting, and monitoring is required to ensure wind firmness and prevention of damage to the residual mature stand.
Diameter limit sanitation harvesting is a selective harvest in which infested spruce of a minimum diameter or greater are removed throughout the stand. Older attacked spruce of a minimum diameter may be included in the prescription as a salvage component or left standing for various ecological reasons.
Single tree selection sanitation harvesting is a selective harvest designed to extract infested spruce throughout the stand regardless of their diameter.

Baiting (associated with harvesting) – The use of semiochemical tree baits in grid patterns in spruce beetle infested stands is a temporary holding tactic until the stand can be sanitation logged. Baiting should be done on a 50 m ´ 50 m grid throughout the entire infested portion of the stand(s) proposed for sanitation logging.

Appropriate situations for deploying spruce beetle baits on standing trees:

smaller, distinct blocks having a light scattered attack with no heavily- infested patches
stands where it doesn’t matter if many additional trees are attacked within the stand prior to clearcut sanitation logging
stands where sanitation clearcutting is clearly scheduled to occur at the soonest opportunity after the beetle flight and before emergence for hibernation
stands where the licensee/contractor could not otherwise pick up smaller patches of attacked conventional trap trees in early winter (for whatever legitimate reason) and/or where early deep snow would make trap tree retrieval difficult (e.g., at the bottom of a shaded slope).

Trap trees

Trap trees are living, large diameter spruce which are felled to attract spruce beetle. Spruce beetle prefer downed material which they attack more extensively and at a greater mean attack density than they do standing spruce. Trap trees felled into the shade and left unbucked and unlimbed may absorb up to 10 times the number of beetles a standing tree will. Trap trees will effectively attract beetles from up to 0.4 km away, and less effectively for up to 0.8 km. Two types of trap trees are used, depending on the availability of access to remove them: conventional and lethal.

The following trap tree considerations apply to both conventional and lethal trap trees:

Sites should be clearly flagged and must be mapped to facilitate felling and, in the case of conventional trap trees, subsequent extraction or treatment.
Trees must be uninfested.
Trees should be greater than or equal to 35 cm dbh, and have thick bark.
Trees should be cut with low stumps.
Trees should be felled in a direction which provides the greatest amount of shade. If possible, fell conventional trap trees so that their butts face towards a road to facilitate eventual skidding.
Trees should not be bucked or delimbed.
Trees should be felled as close to an infestation as possible and no farther away than 0.8 km.
Shaded, freshly windthrown spruce can be used as trap trees and must be removed or treated with the other traps.

Trap tree quantities

The number of trap trees (conventional or lethal) to be felled mainly depends on the size of the attacking beetle population, which is usually estimated by the number of adjacent infested standing trees. One trap tree should be felled for every 10 infested standing trees for static infestations; and ratios as high as 1:4 for more severe infestations. Felling more than one trap tree for every five standing infested spruce will excessively deplete the canopy and reduce shading.

Trap trees are most effective when deployed against heavy infestations in very small areas or against light to moderate infestations over larger areas. In heavy infestations over larger areas it may not be efficient to fell sufficient traps to absorb such a large population.

Conventional trap trees

Conventional trap trees are deployed to:

contain emerging beetles in cutblocks prior to sanitation logging
protect adjacent healthy timber or reserves
“mop-up” beetles emerging from stumps and slash following sanitation logging.

Conventional trap trees must be subsequently removed or treated to kill trapped beetles prior to emergence.

Conventional trap tree felling and extraction periods

Conventional trap trees should be felled in late winter (e.g., early March) so that such trees lie on top of most of the accumulated snow.
Infested traps should be removed early in the next winter logging season of the same year (e.g., late November) before they become covered with excessive snow and frozen in place.
Conventional trap trees left on site after April of the following spring may yield early-maturing one-year cycle adults which could attack adjacent timber.
In any event, conventional trap trees must be removed or treated prior to beetle emergence.

Conventional trap tree deployment tactics

Although felling trap trees in a dispersed pattern throughout an infested stand may be the most effective deployment, this treatment is constrained by the problems of economics and safety in felling, and difficulties in trap tree extraction if the entire stand is not scheduled for harvest. Therefore, other tactics may be employed.

Trap tree patches are usually 12–25 trap trees felled into standing timber in a single, narrow, and shaded group adjacent to a road, to facilitate eventual skidding and hauling. Of all the deployment tactics, trap trees felled in patches have the best shading and, therefore, have been the most effective at absorbing spruce beetle adults.
Pre-felled road rights-of-way, landings, and cutblock strips can be used during cutblock pre-development as relatively large scale conventional trap tree programs. Their sheer numbers can usually compensate for lack of ideal shading.

Lethal trap trees

Lethal trap trees are injected with the arsenical MSMA prior to the beetle attack period. This treatment kills the beetles as they attack the trap, thereby avoiding the need for subsequent extraction or treatment of infested material.

Lethal trap trees are large diameter, uninfested spruce in which a continuous ax- frill is cut in the phloem as close to the ground as possible in early spring. The frill is immediately injected with 1/4-strength MSMA (monosodium methanearsenate) at a rate of 1 ml of formulation per 2.5 cm of circumference. Applications are normally conducted in mid-May once translocation starts. After a two week period to allow translocation of the MSMA throughout the bole, trees are felled into the shade and left intact. Attacking adult spruce beetles are killed and, therefore, lethal trap trees do not require further treatment.

Lethal trap trees should be no further than 0.8 km from infested trees. As with conventional trap trees, lethal traps are most cost-effectively felled in patches. Where helicopter access is necessary, it is advisable to select only those helispots where a minimum of 10–15 lethal trap trees are required.

Lethal trap trees should only be deployed in inaccessible locations where conventional trap trees could not be extracted. Lethal traps should be used to contain pockets of emerging spruce beetle, and/or to protect valuable spruce stands until road access can be constructed (usually within 2–3 years).

Prevention

Hauling and milling restrictions

Restrictions on hauling and milling of spruce beetle infested logs are occasionally necessary if the hauling destinations are located adjacent to high- hazard spruce stands. If hauling is permitted at the beginning and end of the spruce beetle flight, there must be a stipulation that the logs be milled within 24 hours.

Utilization

In spruce beetle sanitation-logged areas, there may be long butts, tops greater than 10 cm in diameter, decked logs, and stumps containing mature spruce beetle adults. Maturing beetles will emerge to attack new hosts unless the infested material is either burned, removed and milled, or otherwise treated. Prudent utilization requires that:

stumps be cut as low as possible
a 10 cm diameter top utilization be used and all tops be scattered on the block or piled and burned on landings
long butts (if permitted) should be piled and burned on suitable landings or elsewhere
all recently killed host material such as recent edge blowdown, larger broken tops, and spilled logging loads should be removed before they are attacked.

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