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Forest Health Information Management

Assigning Strategies to Beetle Management Units

October 2003

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A cornerstone to the management of bark beetle infestations in B.C. is the correct assignment of beetle management unit strategies.  This page describes the objective of each strategy, the physical boundaries of a BMU, and other criteria that define the strategy.  Some of this information is new and is not presented in the   biologically-based Technical Implementation GuidelinesDue to the size and distribution of the current outbreak in the central interior, BMU criteria and a two step procedure had to be developed to accommodate the influence of immigration pressure from large infestations nearby.   

What is a Beetle Management Unit?

A Beetle Management Unit (BMU) is a planning and reporting unit for operational beetle management. Its purpose is to facilitate the implementation of beetle management activities. Resource management objectives should be consistent throughout the unit, although specific parks should be included within a BMU. Parks should only be considered separate BMUs if size and circumstance indicates relevancy. Strategies should be evaluated for compatibility with adjacent BMUs.

How are the boundaries of a BMU derived?

In theory, BMU boundaries are independent of other administrative boundaries and are identified through evaluation of infestation maps and resource inventories. BMU boundaries are then drawn around areas with more or less consistent levels of beetle infestation levels and management objectives. Such boundaries are reviewed annually and adjusted based on the most recent annual aerial overview surveys.

However, in practice, BMU boundaries are customarily congruent with the boundaries of Landscape Units (LU) due to the availability of the spatial and attribute data necessary for setting the BMU strategy. The strategy, and, therefore, the recommended treatment options, is selected after consideration of the status of the outbreak in the BMU (LU) and the estimated feasibility of achieving specific objectives inherent in the BMU strategies. The use of LUs (or other similar administrative or topographic boundaries) is a logistical shortcut that avoids the chore of revising BMU boundaries each year.   However, BMU strategies usually need to be revised annually based on the most recent annual overview survey. The estimated levels of red attack are used as a guide to the levels of expected green attack prior to any ground surveys.

Can existing BMU boundaries be modified?

Yes, the boundaries can be modified to incorporate units with similar strategic objectives but the BMU should contain a minimum of 15,000 ha of the susceptible host (see general criteria below).

Can BMUs for different bark beetle species be different?

Yes, as described above, the BMU boundary encloses a homogeneous unit of susceptible timber type and infestations that can be assigned the same management objective.  A suppression BMU for Douglas-fir Beetle (IBD) can look very different from one for mountain pine beetle (IBM) due to the distribution of the two main hosts.  

How are the strategies influenced by adjacent outbreaks?

Some modification of the original principles behind BMUs may be necessary. Initial development of the various strategies was based on infestations arising and spreading in an area independently. In this current outbreak, there is a large influence imposed on some BMUs from adjacent or relatively near BMUs where large populations of beetles are dispersing over long distances to augment and increase local populations. This, obviously, may drastically alter the practicality of meeting individual BMU strategic objectives.

What are the Performance Measures and Consequences if they are not achieved?

The BMU performance measures (i.e., % of known infestations treated prior to beetle flight per year) are the strategic targets that, if met, will achieve the desired beetle management objectives. Failure to meet the results is an admission that the objective was unattainable despite the best efforts of all parties. The consequence of failure is a downgrading of the BMU strategy to a less intensive objective.  It is imperative that strategies are selected with a realistic understanding of the capacity for treatment and failing to do so would result in a waste of valuable resources that could have been allocated to areas where success would be more probable.

See BMU Performance Measures for specific details.


Revised criteria to consider when delineating BMU boundaries

General Criteria:

 

Factor

Suggested Criteria

Unit size A suggested minimum BMU size incorporates approximately 15,000 ha of susceptible forest type.
Beetle Infestation Status The beetle infestation status should be relatively constant over the designated land base. That is, it can be scattered low attack throughout, scattered low attack with a few patch infestations, a few scattered infestations with many expanding patches, large block areas with old dead and some expanding patches, or just large areas of continuous attack.
Topography BMUs may be defined by points of elevation (e.g., discrete drainages) or amalgams of drainages with similar characteristics.
Feasible Objectives
  • Access
  • Harvest capacity
  • STT capacity
  • Protected Areas
An overriding consideration in the assignment of an appropriate strategy is: "can the strategic objectives by realistically reached?" This must consider the level of infestation, harvest and treatment capacity, presence of contributing Protected Areas, and proximity to large outbreaks where substantial long distance dispersal is likely.

Criteria by BMU Strategy:

STEP 1 - Based on the Provincial Aerial Overview Survey data, determine if the performance measures can be met using available resources.  Adjust the strategy designation according to the level of management possible.

STEP 2 - If in Suppression BMUs the most current bark beetle ground surveys indicates the average Green: Red exceeds 10:1, revise the strategy .  Use the criteria described in the table below.  The purpose is to evaluate whether or not the BMU is being over-run by large, unmanaged infestations thereby making suppression or holding objectives very difficult or impossible to attain.

Note: the following table deals with Suppression and Holding Strategies only. Salvage and Monitoring strategies and their criteria should be more self-evident and are indicated when beetles have not been detected to date or the outbreak has basically run it’s course in the BMU, or where the outbreak has overrun any capacity to significantly reduce the continued spread. At that point, priorities are clearly to derive maximal value from the resource before degradation.

 

Factor Definition

Factor

Suppression

Holding

Green:red ratio (average for the BMU) <10:1,  remains suppression. 

If >10:1, it becomes Holding.

<10:1 i.e., not being influenced by an overwhelming source of beetles.

> 10:1, strategy is now Salvage (treatments will have minimal impact on expansion rate of the infestation)

Harvest/treatment capacity AAC/ trt capacity is >estimated green attack.

The current AAC and STT resources can treat all of the known current attack and drive the population to endemic levels.
AAC/ trt capacity is = 0.5 to ~0.7 x estimated green attack. (e.g., 1000 m3 AAC/Trt vs. 2000 to 1,430 m3 of current attack)

The current AAC, at best, can keep up to the rate of increase. 

No STT recommended.
Infestation Distribution Mostly spots with relatively few patches

No grey

Mix of small spots, small and medium patch infestations; little grey attack

Suppression: Objective is to reduce populations and maintain them at a relatively low level. Target is to treat >80% of known infestation centers in each year. All harvest and treatment is directed at green attacked trees

Holding: Objective is to maintain the infestation to a relatively static level by treating ~50-70% of known infestations in each year. That is, the level of harvest and/or treatment is equal to the rate of infestation expansion. Harvesting should be concentrated in green attacked trees.

Salvage: Objective is to salvage for value recovery as the highest priority. Indications are that holding the infestation static will fail due to influx of populations from heavily infested BMUs in proximity. Emphasis is more to retrieve values at risk and maximize Crown revenues by directing harvest towards killed stands prior to significant degrade.

Monitoring:  Objective is to only record the change in attack level with no beetle management being attempted.


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Last updated July 11, 2013
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