[Spacing Guidebook Table of Contents]

Guidelines for including spacing in stand management prescriptions

Spacing may be done on free growing stands, or stands that do not have a basic silviculture obligation, to meet landscape level objectives. The stand level objectives for a spacing treatment are chosen considering a particular stand’s site conditions, health and biodiversity, and its potential to meet landscape and integrated resource management objectives. Stand level objectives should be consistent with the landscape level objectives.

The following is a list of factors that should be evaluated before including spacing in a stand management prescription.

These criteria are presented to provide general guidance for preliminary evaluation and ranking of stands. Appendix 1 lists the ranking criteria and considerations for use in the development of stand management prescriptions.

Biological criteria

Guideline 10

Consider biological factors when evaluating/ranking stands for spacing. These factors are:


Species that have high wood values and have good response to spacing should be given treatment priority. Examples on the Coast are Douglas-fir and hemlock stands, which capture high market values and show good response to spacing. In the Interior, lodgepole pine can be severely overstocked and individual trees respond rapidly to thinning, particularly in the early years. Douglas-fir in dry Interior areas often grows as a suppressed overstocked understorey and responds well to spacing.

Site quality

The growth response to spacing depends on the site quality. In general, trees on good sites show more response than trees on poor sites. Good sites should therefore receive highest priority for spacing. Spacing of pre-October 1, 1987 dense lodgepole pine stands (>10 000 stems per ha) on poor sites in the Interior can be done to avoid repression of height growth.

Stand density

Spacing stands with high initial densities can result in a large individual tree growth response. High density stands should be given a priority for spacing as long as the treatment can be done before competition becomes too severe. Factors such as per cent live crown and height/diameter ratio will indicate the amount of competition occurring in a stand.

Per cent live crown: The per cent live crown is related to the degree of crowding or competition and is a good indicator of a tree’s capability to respond. Per cent live crown is the ratio of live crown length to total tree height. When estimating live crown length, small or isolated lower branches below the main crown should be disregarded. In general, the per cent live crown of a crop tree is likely to diminish in older and denser stands, resulting in a decreasing response to treatment. A 30 per cent or less live crown for crop trees generally indicates a tree that has had significant competition.

It may be acceptable to space very dense lodgepole pine stands (>10 000 sph) with residual live crowns less than 30 per cent. Spacing of such stands may reverse height repression and is therefore a priority, providing that the treatment is done on young stands.

Height/diameter ratio: The height/diameter ratio is measured by dividing the tree height by the stem diameter at breast height with height and diameter in the same units (e.g., centimetres). This ratio changes with the degree of competition over time. At a given height, trees that have been crowded will not have as large a diameter as trees that have not been crowded. The crowded trees will therefore have a higher height/diameter ratio. Height/diameter ratios are indicative of a tree’s ability to withstand wind and snow and ice loading. Concerns should be raised when ratios are above 90.

Height and age of stands

It is preferable to space shorter stands to avoid high treatment costs, to minimize slash management problems and to avoid growth loss due to the onset of competition.

The stand’s ability to respond to spacing is partially a function of the stand’s age. Younger stands should be given higher priority due to their ability to respond more favorably to treatment. However, stands should be old enough that crown lift has begun (to avoid problems of live branches on stumps), and significant ingress is complete.

Forest health factors

Forest health factors include insects, disease, wildlife, and abiotic conditions. Consult the silviculture prescription for information on damaging agents that may be problematic due to spacing. The prescription may also contain recommendations on spacing techniques and timing that could affect forest health factors or their impact. Information on forest health factors following stand regeneration is collected through silviculture or pre-stand tending surveys and is stored in data bases such as the Integrated Silviculture Information System.

The type and degree of damage predicted for a particular pest will determine if, when, and how a stand should be spaced. Spacing can increase or decrease risk of further damage. Some general precautions should be taken to determine whether spacing may assist in control or may leave the stand susceptible to infestations. If a silviculture survey of the stand has not been completed recently, complete one before spacing. Use the survey results and any other information, such as the Forest Health Charts in the Establishment to Free Growing Guidebook, to identify any potential problems that may confound stand spacing.

Results from the silviculture survey or other initial forest health assessment may indicate the need for additional forest health surveys.

Forest health survey results should be used, if necessary, to stratify the area into different treatment units. Stratification may be necessary if areas covered under the silviculture prescription or stand management prescription have different levels of infestation, triggering different treatments or no treatment in a portion of the block.

Threshold levels are developed for a variety of forest health factors. Details on these thresholds and related surveys are presented in the various forest health guidebooks and the Silviculture Surveys Guidebook.


Root disease: Control of root disease should have occurred at the prescription and stand regeneration stage. If this has occurred successfully there should not be any further root disease problems for spacing. If however, a current silviculture survey shows one to five per cent of host species infected with armillaria or phellinus, or any presence of tomentosus infection, consult the Root Disease Guidebook for further direction. Treatment strategies vary depending on the specific root disease. Strategies outlined in this guide are:

Dwarf mistletoes: Any residual, overtopping dwarf mistletoe-infected tree that jeopardizes the health of young trees should, if possible, be removed. The prescription or forest district staff should be consulted to determine why the residual trees were retained at the time of harvesting, before a recommendation is made to remove them.

Once overtopping infection sources are removed, free growing trees should out-grow the dwarf mistletoe infections. Consider removing infected trees during spacing. Refer to the Dwarf Mistletoe Guidebook.

Comandra blister rust, stalactiform blister rust and western gall rust: A tree is considered infected if:

Disease incidence and recommended treatment tactics for all three rusts on lodgepole pine:

White pine blister rust: Rust-free western white pine should be retained wherever it is found. This is done to increase biodiversity and on the possibility that the retained tree may exhibit signs of genetic resistance to the rust. For western white pine to be considered a potential crop tree, it must normally be pruned as a treatment for white pine blister rust.

Spacing has been shown to increase white pine blister rust infection rates through increased spore movement through the thinned stand. It is therefore recommended that white pine trees that are of suitable size and are free from stem infection be pruned at the time of the spacing treatment. This is particularly important where the retention of white pine is necessary to meet stand level objectives.


Defoliators: Consult the forest district regarding the current phase and outbreak cycle (periodicity) of particular defoliator species. When current or predicted defoliation (in the coming year) is moderate or greater, spacing should only be prescribed in conjunction with direct control programs for the particular defoliator (see Defoliator Guidebook).

Bark beetles (in partial cutting silvicultural systems)

Douglas-fir beetle: Ensure that spacing slash is less than 10 cm diameter. All spacing slash of a diameter greater than this must be removed or destroyed when Douglas-fir beetle is present in the stand or area.

Mountain pine beetle: Spacing should be done in conjunction with sanitation treatment of the stand. Residual stems must not be damaged during the spacing or sanitation process.

Review the Bark Beetle Management Guidebook and consult forest district staff.

Spruce and lodgepole pine terminal weevils

Spacing should not be conducted in high risk stands, or stands where weevil damage is occurring or expected, until the incidence of the damage is clearly declining. An attack threshold related to spacing for lodgepole pine terminal weevil is 10 per cent. Conduct surveys of weevil damage incidence according to procedures described in the Terminal Weevils Guidebook. Weevil damage incidence should not be estimated in stands <15 years old. Surveys conducted in five-year intervals should allow a determination of a declining population. Weevil attack may delay spacing for periods of 5–10 years with lodgepole terminal weevil and up to 15–20 years with spruce weevil following the completion of the free growing survey.

Other insects

Consult regional guidelines, or discuss the issue with forest service regional and district staff.


Treatment thresholds related to spacing lodgepole pine have been established only for red squirrels. The decision-making profile for squirrel damage is presented in the Pests of Young Stands Guidebook. For other wildlife damage problems, contact forest service regional or district staff.

Operational considerations

Operational factors such as project and block size, access, and slope affect costs, and should therefore be individually considered.

Factors affecting costs of spacing projects:

Fire protection

Concentrations of slash resulting from spacing operations can present a fire hazard to the stands themselves and possibly to surrounding values. Natural events will diminish this hazard over time. In the meantime, it is prudent that forest managers be aware of the hazard and attempt to mitigate it. Silviculture prescriptions or stand management prescriptions must accurately prescribe the best treatment for the site that addresses all concerns, including fuel loading and long-term fuel management in the area.

The complete elimination of hazard is not practical or possible. These guidelines are intended to identify the factors that should be considered in determining an acceptable level of hazard and what considerations should be incorporated in stand management prescriptions or silviculture prescriptions.

Estimating fire hazard

The information from the FS 748, Pre-Stand Tending Survey, and the summary of these field cards on the FS 770 Pre-Stand Tending Site Description Prescription can be used to determine fire hazard and risk for a site scheduled for a spacing treatment. Most, if not all, sites will be moderate or high hazard and therefore strategies must be prepared for managing fuel levels on the area (Forest Fire Prevention and Suppression Regulation).

The following site-specific factors should be considered when determining the amount of risk inherent in a site and the potential strategies to, if necessary, reduce this risk:

Location: Proximity to people or other resource values, biogeoclimatic zone, degree of isolation, proximity to unabated hazards.

Access: Ease of access, amount of travel in area, existing or future deactivation.

Slope: Steeper slopes increase the rate of fire spread.

Aspect: South and West slopes are generally more hazardous.

Block size: Larger openings create more contiguous slash.

Fuel loading: Amount of slash increases with the size of the stems and as more stems are felled. Depth of slash can be influenced by falling pattern.

Species: Combustibility and fire intensity is impacted by tree species. In reducing order of combustibility: cedar, pine, fir, spruce/balsam, hemlock, and deciduous.

Time: Slash loading reduces over time; the rate of decay varies by site parameters listed above.

Guideline 11

Strategies to reduce fire risk

When reviewing the options, the benefits of hazard reduction must be weighed against the costs. Some costs are minimal and easily incorporated while others are significantly higher to minimize hazard. Not all costs are necessarily direct contract costs. By foregoing or rescheduling treatments, there may well be opportunity costs to stands or portions of stands in terms of stand growth foregone. Refer to the Fire Management Guidebook for additional information. The aim is to achieve an acceptable standard of hazard reduction by using combinations of fuel modification, risk reduction and prevention strategies. Consider the following factors when developing a strategy to reduce the amount of risk created and the duration of the risk.

Access restriction: Deactivation or temporary road closures.

Prevention: Signs, forest closures, campfire bans or increased patrols.

Block size: Size of openings can be limited where applicable.

Buffer strips: Unspaced strips can be left along roads. The need for and width of the strip would vary depending on the severity of the hazard and the amount the road is used. Widths could vary from 5 to 20 metres. The strip is usually measured from the edge of the road running surface. Use roadside features such as cutbanks as natural buffers where possible.

Roadside fuel reduction: Slash can be pulled to road side and burned or chipped. Slash can be pulled into the block. The width of the strips varies from 0 to 20 metres measured from the edge of the road running surface.

Fuel modified in block:

No spacing permitted: Risk may be so great that the stand should not be spaced.

No restrictions: Risk may be so low that no special measures are required.

Guideline 12

Some circumstances may require that greater than 500 hectares be disturbed or treated. Examples of such cases are large fires with dense natural regeneration that require spacing, or drainages that must be treated before access is removed. If the 500-hectare recommended limit is exceeded, the strategy for reducing risk must reflect this.

The Fire Management Guidebook defines fire resistance areas. For the purposes of spacing, there should be a minimum of 5 years since spacing and the trees should be a minimum of 5 metres tall.

Guideline 13

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