[Pruning Guidebook Table of Contents]

Methods and techniques

Timing of pruning projects

The best conditions for pruning occur during cold weather when tree growth is minimal and the tree is dormant. Pruning should be avoided in the spring when the bark is loose and stem damage may be high. Experienced contractors using shears may be able to keep stem damage to acceptable levels when doing spring pruning. Pruning at times other than when the sap is running minimizes bark damage caused by the pruning equipment. Clogging of tools with tree sap is also minimized. Silviculture workers benefit when pruning occurs during seasons not suited for other silviculture work. Stem damage from sun scald may occur in summer months if tree boles are suddenly exposed to severe hot and dry conditions. Amount of damage due to sun scald tends to be species specific. Fall and winter are preferred pruning times.

The diameter of the knotty core should not increase from the first to the second lift, when pruning is done in multiple lifts. This ensures that the size of the knotty core is maintained through the second lift on the stem (Figure 2). Figure 3 shows the impact on clear wood timber production from late and on time pruning regimes.

The cost of pruning has currently restricted treatments funded by the B.C. Forest Service to a maximum of two lifts. To ensure a marketable product can be obtained at the end of two lifts, tree height has been used as the primary factor to determine when the second lift should occur.

Guideline

Pruning should not be done in the spring when the bark is loose and the potential for stem damage is high.

When scheduling second lift pruning consider:

Figure 2. Time the second lift of pruning to maintain the same size of knotty core as the first lift. The second lift should occur no later than when the diameter immediately below the first whorl of branches at the start of the second lift equals the diameter at the start of the first lift.

Maintaining wildlife habitat

Security cover, forage concerns and wildlife trees must be considered before pruning. Pruning activities should also be timed to minimize impacts on known wildlife habitats during breeding, calving, and other sensitive seasons of maximum use.

Security cover

The main impact of pruning on wildlife habitat is the reduction of security cover. Security cover offers concealment from hunters and predators. Some wildlife, such as deer, prefer to be near cover at all times. The existence of cover close to forage and water increases the utility of these resources.

Figure 3. Distribution of clear wood from late and on time pruning regimes.

Where required through consultation with the appropriate Ministry of Environment, Lands and Parks staff, a visual buffer should exist along main and secondary roads in areas with high populations, or hunting pressure, of big game species. A visual buffer, also known as a visual screen, may be provided by topography or vegetation (Figure 4) which blocks the viewing of the interior of the treatment area. In the absence of naturally occurring visual buffers, unspaced buffers should be left at the spacing stage. If such unspaced buffers have not been left, then spaced areas can be left as unpruned buffers. The buffer size depends on the specific site conditions. The width of the buffer should be sufficient that a person or animal walking along the interior edge of the buffer is at least 90% screened from view from the road.

The access management plan for the area should be considered when determining the need for visual buffers along roads. Visual buffers may not be needed if roads are deactivated after the pruning treatment.

A degree of visual buffering may also be achieved by leaving some unpruned trees throughout the stand. Such trees would include poor quality stems (wolf trees), unsuitable tree species (hardwoods), or residuals. Leaving small patches of unpruned trees may also be required to create a visual buffer within the stand or around important wildlife areas such as wildlife trees and riparian zones.

Restricted harvesting practices in riparian management zones will reduce the economic feasibility of pruning in these areas.

Figure 4. Vegetation or topography can create a visual buffer (from Nyberg and Janz 1990).

Guideline

A visual buffer of unpruned trees along roadways may be necessary to reduce wildlife visibility from the road.

Pruning and lichen

Pruning offers only a minor benefit for creating wildlife forage by increasing light to understorey vegetation. However, pruning reduces the amount of arboreal lichens by that which would grow on the lower limbs. These lichens provide an important winter food source for woodland caribou and mule deer. If areas have been identified as woodland caribou or mule deer winter range then consult forest ecosystem specialists before pruning.

Guideline

Pruning should be restricted in areas where lichen is identified as important wildlife forage.

Wildlife trees

A wildlife tree is a standing dead or live tree with special characteristics that provide valuable habitat for conservation or enhancement of wildlife. In most cases wildlife trees are identified prior to pruning. However, if spacing occurs after pruning, the wildlife trees must be identified and danger trees removed or no treatment zones established prior to the pruning treatment.

Wildlife tree management includes both the retention of suitable wildlife trees at the time of harvest and silvicultural activities, and the recruitment of suitable replacement wildlife trees over the rotation period.

Generally, the safest and most operationally feasible method for managing wildlife trees is to leave a mixture of live and dead standing trees in a clumped distribution (reserves). The location and size of the reserves in a stand will depend on specific site conditions such as availability of high quality wildlife trees, and wind firmness. The amount of wildlife tree area required for any specific unit depends on the level and distribution of existing and planned harvesting on the surrounding landscape. Wildlife tree reserves may be located at the edge of the stand, in areas that are difficult to access or in less productive areas. This location can be done to minimize the impact of the mandatory no-work zone. Refer to the Biodiversity Guidebook for more information on wildlife trees.

Guideline

Maintain wildlife trees in wildlife tree reserves.

The location of these reserves should be consistent with the Biodiversity Guidebook.

Block identification

The area pruned must be suitably identified for future logging operations in order to extract the full value of the pruned stand. The pruned area must be recorded on maps and marked on the ground. Any areas within the block which have not been treated, such as buffers, should also be mapped. Treatments should occur over whole openings, or parts of openings that are clearly delineated by roads, topographic breaks, or similar features. This should avoid sorting confusion during harvesting.

In addition to their location, the size of the trees (diameter breast height and pruning height) at the time of pruning must be known. At rotation age, the amount of clear wood available in each log cannot be visually assessed until the log is processed. The value at rotation cannot be forecast without initially documenting the size of the knotty core.

Guideline

Pruned areas must be clearly marked on forest cover maps.

The dbh of trees at pruning and the pruning height should be documented.

Crop tree selection

Where stocking control is required, pruning can be done before or after spacing. In most cases spacing is done before pruning. If pruning is done first, the pruner is responsible for crop tree selection and should not prune the trees that will later be spaced out. The pruner must select trees following the same criteria for crop tree selection given spacers.

The number of branches in a whorl must also be considered; the most desirable tree has few. Trees with many branches per whorl should be left if pruning may girdle the tree. Pruning costs may also become excessive with many branches to prune.

Guideline

Do not prune a tree if it will result in girdling of the stem.

Pruning mixed species

Most forest stands have a mixture of tree species. The most desirable stands to prune will have a majority ( > 60%) of the desired species. Regardless of the species mix, the key is to maintain rapid tree growth by spacing stands to recommended densities for pruning. Stands at recommended densities for pruning should have all stems pruned if there is concern that pruned trees will lose dominance to unpruned trees. Pruning causes some height and diameter growth loss for 1–2 years after pruning. Unpruned codominants can overtake the selected pruned trees and reduce their growth. This exchange of dominance reduces the return on the pruning investments.

If a species making up a minor component of the stand has adventitious buds these may be left unpruned.

Guideline

Prune all stems in a stand if a change of dominance may occur between pruned and unpruned trees.

Pruning technique

When pruning, cut branches parallel to the bole or main stem and as close as possible without significantly damaging the branch collar (Figure 5). This technique will minimize the time needed for occlusion, or healing over of the scar, and maximize subsequent growth of clear wood. Poor pruning techniques, such as leaving long coarse stubs or scarring the tree, can decrease or eliminate the gains in wood quality, and in some cases kill trees.

Proper lift height must be defined for each stand considering the length of clear wood desired and the height of the trees. If a single lift is planned, the minimum length of clearwood should normally be 3 metres.

Use pruning shears or saws. Do not use an axe or machete to prune branches as these tools can damage trees. These tools may fracture the base of the branch inside the stem, leading to decay and reducing clear wood quality. Do not use chain saws unless they have been modified to successfully protect the stem from scarring. Shears cut close to the branch collar of the tree without the risk of scarring and form a clean cut surface. Cut surfaces that are jagged or have torn fibres take longer to occlude.

Guideline

Do not use tools such as axes and machetes that remove branches using an impact force.

Long-handled or telescopic pole pruning saws, or lightweight ladders with pruning shears or saws can be used for the second or subsequent lifts.

Figure 5. Proper pruning of a branch is a cut as close as possible to the branch collar staying roughly parallel to the stem.

Monitoring and reporting

Monitoring

A pruning project should be monitored for compliance with any treatment standards set out in the stand management prescription or silviculture prescription. The default treatment standard is listed in the guideline below. The B.C. Ministry of Forests will perform monitoring of pruning projects using the methodology described in the Ministry of Forests Silviculture Contract for Stand Tending – Pruning, Schedule A (FS 348A). The minimum acceptable performance quality is 75%. The main considerations are listed in the following guideline.

Guideline

Properly pruned trees must have:

Standard

Guideline

The minimum acceptable performance quality is 75% as measured by the Ministry of Forests procedure.

Reporting of accomplishments under SMPs

Reporting of stand management prescription accomplishments on free growing stands is required for major license holders. The Silviculture Practices Regulation requires that a treatment report is submitted quarterly to the district manager. This report must:

The submission dates are April 15, July 31, October 31, and January 15. Pruning done by the Small Business Forest Enterprise Program should be reported following ministry procedures.

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