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.
Consider biological factors when evaluating/ranking stands for spacing. These factors are:
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.
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.
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.
Factors affecting costs of spacing projects:
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.
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.
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.
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.