Bark Beetle Guidebook: Chapter3c

[Bark Beetle Management Guidebook Table of Contents]

Douglas-fir beetle

Hazard rating

Hazard rating identifies those stands where substantial losses can be expected to occur if an outbreak of Douglas-fir beetle occurs. Hazard rating of stands is intended to identify those stands that are highly susceptible to attack by Douglas- fir beetle and should be considered a valuable planning tool. Once all Douglas- fir 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, elevation, and other factors.

The overall hazard of a Douglas-fir stand may be evaluated using a number of parameters. These parameters are given in Table 15 along with rating values for low, moderate, high, and very high hazards. These rating values are applied in the following formula:

Stand Hazard = D * B * A * O * S * T * G * P

P = stand purity or the % of total stand basal area composed of Douglas-fir based on all trees with a dbh greater than or equal to 7.5 cm.

Table 15. Parameter values for hazard rating Douglas-fir stands

The appropriate values for each factor are multiplied together to generate a hazard index that will vary between 0 and 100. These are qualitative hazard values: the higher the index, the higher the hazard.

Risk rating

Stand risk is the probability that the Douglas-fir stand will be attacked based on the proximity of a Douglas-fir beetle infestation. The risk of attack may be determined by comparing survey information regarding Douglas-fir beetle infestations with a forest cover map which has been coded for hazard.

After the hazard and risk rating are completed, management strategies can be developed to minimize beetle losses in priority stands. Danger ratings, or immediate priorities for treatment or management, may be identified by combinations of hazard and risk. The higher the danger rating, the more important it is that action be taken. Table 16 indicates how hazard and risk assessments can be combined to identify priorities for management.

Table 16. Management priority ranking based on stand hazard and risk

Ground detection

Ground surveys are the necessary follow-up to aerial surveys and prerequisite to control action. All mapped infestations of three or more infested trees should be ground-checked to verify beetle activity and determine the infestation size.

There are three fundamental objectives for any ground survey:

accurate identification of the beetle and host
determination of damage severity
location and delineation of damage to facilitate control action.

Development of a survey plan for Douglas-fir beetle should be based on the following factors:

larger infestations should be surveyed first
groups of three or more current attacked trees should be surveyed if possible
high hazard stands
high values at risk should be given priority
infestations which have good access should be given priority
areas with a history of bark beetle activity, and areas where management efforts have been invested should be given priority.

Ground surveys for Douglas-fir beetle

Walkthroughs confirm the previous or suspected identification of beetle and host, collect information to set further survey or management priorities, and estimate population trends.

Walkthroughs should pass through the infestation and the susceptible forest cover types surrounding the infestation. Establish two lines, at right angles to each other, through the expected centre of the infestation. Examine trees and estimate:

presence of successful attack
average stand diameter
average stand height and density (stems per ha)
percentages of current attack, old attack, and healthy trees
other forest health considerations.

Probes provide more detailed information than walkthroughs and may be appropriate for laying out treatment areas.

Probes are systematic strip surveys that provide more precise estimates of attack levels, beetle trends, and residual stand values. Probe lines should be established so that the infestation is included in the central part of the survey area. Ensure that:

survey lines are run at 50 m intervals
survey lines (strips) are 5 m wide
strips are continuous and will run until the edge of the survey area is reached or 100 m beyond the last currently infested tree
all trees within the strip should be assessed for attack status
attacked trees should be recorded by 5 cm dbh classes.

Star probes may be carried out in trap tree sites or small beetle-kill centres after beetle flight to ensure no standing attack is undetected and left untreated or unharvested. Attacked trees identified during these probes should be harvested or otherwise treated.

Establish a 100 m radius around the centre of the spot to be probed.
Inspect all trees within the plot for attack.
If a successfully attacked tree is found, inspect all trees within 100 m of it.
Continue the process until no further attacked trees are found.
Record attacked trees by 5 cm dbh classes.
Measure the heights of two dominant or co-dominant trees.

Management options

Strategies

Strategies for managing Douglas-fir beetle depend on a number of factors:

infestation size
stand susceptibility
values
access
infestation history.

The process of determining the most appropriate approach is illustrated in Figure 6.

Figure 6. Decision framework for managing Douglas-fir beetle.

Management of Douglas-fir beetle follows a general time sequence which is outlined in Table 17.

Table 17. Recommended management activity time table for Douglas-fir beetle

Tactics/treatment options

A variety of options are available to deal with existing or potential Douglas-fir beetle infestations. The selection of the appropriate option depends on the stand condition, level of infestation, condition of adjacent stands, existence of access, and the management objectives for the area. There are four main control methods for Douglas-fir beetle:

sanitation harvesting
trap trees
single tree treatment
post-logging mop up.

Sanitation harvesting

Sanitation harvesting for Douglas-fir beetle suppression maximizes the removal of current-attack Douglas-fir to reduce the existing population and inhibit the infestation expansion. All trees containing beetles should be harvested and milled before the adults emerge in the spring. Logging priority should be given to active beetle infestations and adjacent high hazard stands. Various harvesting methods may be used to remove infested trees.

Trap trees

Trap trees are used to reduce overall beetle population levels. They are large, healthy Douglas-fir trees that are felled into the shade to attract Douglas-fir beetle. Trap trees attract and absorb emerging beetles and must be removed after the end of beetle flight. The beetles are killed during timber processing. Trap trees also mop-up beetles emerging from windthrow, stumps, and slash, thereby protecting adjacent healthy timber.

Here are a number of guidelines for trap tree site location and tree selection:

Place trap trees as close to the infestation as possible.
Fall one trap tree for every three to four currently attacked trees. Green windthrow on site may be used as trap trees and reduce the number of trap trees required.
In chronic beetle areas, or with scattered beetle populations, grid with groups of trap trees at 400 to 600 m intervals.
Trap trees should be felled into the shade in such a way as to facilitate removal or subsequent treatment.
Trap trees should be left unlimbed and unbucked.
Pre-felled rights-of-way, landings, and skid trails can be used as trap trees to absorb beetle populations. Due to the large volume of timber felled during these operations, improper shading should not impede the effectiveness of control.
Trap tree diameters should be greater than or equal to 30 cm.
Large openings should not be created at trap tree sites.
Remove trap trees as early as possible after beetle flight.
Probe the site for spillover/overflow attack in adjacent standing trees before trap tree extraction.

Sanitation harvest or fall and burn of Douglas-fir beetle current attack should be followed by trap tree deployment prior to the next beetle flight. Use one trap tree for every four standing current attack. Do not fell more trap trees than required using this rule of thumb, as providing excessive host material actually increases or continues the beetle problem.

Incorporate trap trees into logging plans, placing trap trees in recently logged and active logging areas where bark beetles are present. Pre-fell rights-of-way, landings, or portions of cutblocks to act as trap trees and absorb beetles. If not included in the trap tree program, rights-of-way are best felled in late summer.

Single tree treatments

Single tree treatments, suitable for dealing with Douglas-fir beetle, are similar to those useful for other bark beetles. The bark thickness of Douglas-fir makes falling-and-burning and bark peeling very difficult and time consuming. These treatments should be considered only when no other option is available. Treatments include:

falling and burning
peeling and burning the bark (seldom used)
single tree removal.

Post logging mop-up is necessary after sanitation or other harvesting which creates suitable host material through accumulations of fresh logging debris or windthrow. Sanitation harvesting in areas with chronic beetle populations should be followed up with trap trees to absorb residual populations. Areas where logging has been completed should be monitored yearly to locate fresh outbreaks.

Sanitation and utilization can play important roles in reducing damage caused by Douglas-fir beetle:

Remove all infested trees and mill logs before beetle flight.
Keep stumps as low as possible, with a maximum height of 30 cm. Peel stumps if possible.
Remove, destroy, or peel bark off all debris containing beetle progeny if it is greater than 20 cm in diameter and greater than 2 m in length.
Tops should not be greater than 10 cm diameter.
Eliminate all infested material from sanitation sites.
Burn all debris piles completely before beetle flight.
Remove for milling, or burn, all infested decked logs and windthrow before beetle flight.
Material should be bucked prior to burning so that the pile is more compact.
Avoid mechanical damage (scars, root damage, and broken tops) to residual trees.

Trap tree sites should be monitored to ensure all infested material is eliminated. Residual stands and suspect trees injured during harvesting and road construction should be monitored and infested trees removed.

Falling and burning infested material may destroy beetle progeny if done thoroughly. If sanitation harvesting options are not viable, then the tree may be felled, bucked into bolts, piled and burned. The bark must be burned so as to completely destroy the phloem. Sanitation harvesting should be explored as an option, if at all possible, because it is difficult to fall and burn for Douglas-fir beetle.

Hauling and milling restrictions are occasionally necessary if uninfested stands are threatened. If mills or log decks are located adjacent to high hazard Douglas- fir stands, hauling and milling restrictions may be implemented. Hauling may be prohibited during the main flight period. Mills must process logs promptly.

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