Case Study Discussion Appendix 1

Discussion of Case Studies

Commercial thinning is not a silvicultural system, even though harvesting is involved. It is merely an intermediate treatment that removes some harvestable volume and improves vigour and growth of leave-trees. This stand tending treatment may, however, be a powerful way to manipulate stand structure within a specific silvicultural system. Commercial thinning is an important treatment in a single tree selection system and various shelterwoods, although it can be used in any system.

Which of the following terms do you think describes a silvicultural system?

seed tree    (yes)
partial cutting
selective logging
clearcut    (yes)
group shelterwood    (yes)
commercial thinning
sanitation cutting
nurse-crop shelterwood     (yes)
group selection     (yes)
crown thinning
high-lead system
selection thinning
new forestry system
strip selection     (yes)
retention system    (yes)

See the discussion of reserves in Part 2.

This silvicultural system should be called a seedtree with reserves. This system would be called a clearcut with reserves since now the block will be managed as a clearcut, rather than intending the leave-trees for natural regeneration. The intent of the system (generally for regeneration) is the cornerstone for its label. 

  • larger, dominant trees
    • are conditioned to open windy environments
    • tend to have deeper, more extensive roots
    • tend to have a greater taper
  • windfirm trees (see previous) but also consider:
    • species crown and rooting characteristics
    • absence of root or stem rots
    • topographic location relative to prevailing winds
  • desirable species
    • for all resource objectives
  • desirable physical characteristics
    • to try to maintain good genetic traits
    • to provide an incentive for a removal cut (maybe)
    • to produce "good" seed production relative to what is normal for that species

The number and distribution of leave-trees in seed tree and shelterwood systems depends upon:

  1. All resource objectives for the silvicultural system used
    • aesthetics, wildlife, watershed concerns (clearcut equivalency concerns for increased flows, water quality, etc.)
    • timber management--if you want to retain enough overstorey to maintain stand increment (B-level stocking goal).
  2. Stand constraints
    • primarily windthrow hazard
    • dominance expression--larger trees with high expression of dominance preferred
    • vigour and health of trees
    • stand density and pattern (uniform or clumpy, dense or open)
    • proximity to other stands that may provide protection
    • incidence of insects/disease
    • ability of individuals in the stand to produce seed
    • ability of individual trees to increase incremental growth
  3. Site constraints
    • climatic extremes for moisture, temperature, and light
    • rooting depth of soil
    • prevailing wind speeds and direction
    • terrain difficulty and slope
  4. Silvical characteristics of preferred leave-trees
    • species rooting depths, taper, and crown characteristics for wind resistance
    • the ability of the trees to produce seed
    • species needs for protection
  5. Number and timing of planned harvesting entries
    • if two prep cuts were intended to open a stand slowly, allowing it to equilibrate to endemic winds, many more leave-trees will be left in the first of these cuttings than if one prep cut was conducted
    • if no removal cutting is to be conducted, a shelterwood may be more open than if a removal cut was scheduled

The number and distribution of leave-trees in seed tree and shelterwood systems depends upon:

  1. All resource objectives for the silvicultural system used
    • aesthetics, wildlife, watershed concerns (clearcut equivalency concerns for increased flows, water quality, etc.)
    • timber management--if you want to retain enough overstorey to maintain stand increment (B-level stocking goal).
  2. Stand constraints
    • primarily windthrow hazard
    • dominance expression--larger trees with high expression of dominance preferred
    • vigour and health of trees
    • stand density and pattern (uniform or clumpy, dense or open)
    • proximity to other stands that may provide protection
    • incidence of insects/disease
    • ability of individuals in the stand to produce seed
    • ability of individual trees to increase incremental growth
  3. Site constraints
    • climatic extremes for moisture, temperature, and light
    • rooting depth of soil
    • prevailing wind speeds and direction
    • terrain difficulty and slope
  4. Silvical characteristics of preferred leave-trees
    • species rooting depths, taper, and crown characteristics for wind resistance
    • the ability of the trees to produce seed
    • species needs for protection
  5. Number and timing of planned harvesting entries
    • if two prep cuts were intended to open a stand slowly, allowing it to equilibrate to endemic winds, many more leave-trees will be left in the first of these cuttings than if one prep cut was conducted
    • if no removal cutting is to be conducted, a shelterwood may be more open than if a removal cut was scheduled

It is a common trap: to draw conclusions about the silvicultural system being used based only on what is seen at one point in the stand's life. As a dynamic entity, the silvicultural system cannot be determined based only on the resulting structure at any one point in time. The silvicultural system is named or identified based on the intent for preferred species management; the age-class structure as it changes over time; regeneration requirements; and the distribution and length of retention of the various leave-trees over time.All of these elements have to be considered together to come to a proper conclusions.

  • To allow for retention of dead wildlife trees during harvesting
  • To fit with skidding pattern, thereby increasing harvesting efficiency
  • To better fit with visual quality objectives.
  1. What advantages do simple group shelterwoods have over uniform shelterwoods?
    • they may be easier to harvest and avoid damage to leave-trees and regeneration
    • they may allow for more structural diversity
  2. What disadvantages do you see?
    • Requirements for protection must be carefully assessed, since the final openings created after the removal cut may have little shelter. These openings may require planting with a shade-intolerant species.

Can you think of some suitable stand types for a nurse-tree shelterwood?

  • Lodgepole pine or aspen overstorey with spruce or Douglas-fir understorey
  • Cottonwood or alder overstorey with a spruce or western redcedar understorey
  • Western larch overstorey with a hemlock or western redcedar understorey.
  1. If single tree selection systems produce small groups of trees, when do the groups become large enough to qualify for group selection? Provide your rationale.
    • A continuum of group or clump sizes exists between single tree selection and group selection. Use of the terms will vary between managers depending on the species they manage and the ecology of their sites. At the margin between the two systems the name chosen to describe them probably doesn't matter too much. Generally it is appropriate to call selection systems single tree selection when the group openings created are so small that area-based regulation is impractical and the uneven-aged parameters (q-ratios, etc.) must be used. Some managers may still call such systems small group selection - this is not a huge issue.
  2. When do the group openings in a group selection become so large that they actually would better be called small clearcuts? What is a reasonable size limit? Provide your rationale.
    • This is an important question. A group selection with 5 ha openings to harvest a 200 ha stand stretches the definition of group selection to a point where it is no longer credible.
    • Authors worldwide agree that a group opening becomes a clearcut ecologically when most of the opening (greater than 50%) starts to have the same environmental regime as in a large clearcut. The opening size will depend on the biological requirement of the preferred tree species and other resource objectives. However, if the openings become larger then several tree lengths, they may approach the clearcut environment. The Ministry of Forests therefore defines group selection as having openings less than two tree lengths in width. The ecological considerations related to the influence of the stand edges would depend on aspect and slope.

Do you understand the difference between group selection and group shelterwoods? Study the following diagram and describe the differences.

  • We started out with a relatively even-aged stand in both cases.
  • The only difference here is the timing of the removal cuts and the extent of the removal at each entry.
  • The group shelterwood removed the entire overstorey over two entries within the normal regeneration period (20% of the rotation, about 20 years inthis case)
  • The group selection system removed the overstorey more slowly, spreading the removal uniformly in a series of cuts over the rotation (removing 25% every 25 years in this case)
  • The group shelterwood will have a relatively even-aged stand structure at the end of the rotation, while the group selection will be a clumpy mosaic of different age classes, and will be managed as an uneven-aged stand.

Species selection is not a silvicultural system. You may recognize this prescription as lodgepole pine salvage, and as such is an intermediate harvest entry, not a silvicultural system. This prescription shows a lack of thought, and numerous contradictions regarding long-term structure, future harvesting entries, and regeneration requirements. What we have here is a partial cutting prescription but not a silvicultural system. Without a more detailed plan of further cutting entries the regeneration prescription doesn't make sense.

Key points

  • The strip selection system is typically quite regimented and artificial in appearance once it has been implemented for several cutting cycles.
  • The reserves break up this appearance and give the stand a much more natural uneven-aged appearance.
  • The strip selection system was mostly designed to address windthrow problems. It will be critical, therefore, that large windfirm dominants be chosen as reserve trees.
 

Available Options in Different Stand Types

Key Points

Stand A is a good example of the geriatric BC stands that Weetman (1996) spoke of when comparing options for silvicultural systems in BC and Europe. These stands have fewer options for structural manipulation than the healthier, younger Douglas-fir in Stand B. Considering the centre rot, the redcedar in Stand A is likely much older than 150 years, being missed by wildfires in a sheltered location many times over the years. Much of the redcedar regeneration in Stand A likely developed through layering of the lower branches of larger trees. This regenerationmay be damaged during logging. Stand A has just a few scattered redcedar and spruce dominants that may be able to stand up to an increased windloading (depending on centre/butt rot). The codominants do not appear to be great leave-trees. The structural options here for partial cutting involve some sort of group removal.

The Douglas-fir dominants in Stand B appear to be good leave-tree candidates for uniform systems. Group and strip systems are also not out of the question and could be quite viable. A final decision on the number of options available for each stand would have to consider resource management objectives and risks from wind and other factors.

List the silvical questions we would have to ask before deciding on natural regeneration:

  • What are the desired species and their silvical characteristics?
  • Is there an adequate seed source of the desired species?
  • Is the seed source on-site or adjacent?
  • What distance is the seed expected to travel for adequate stocking?
  • What is the expected periodicity of good seed years (to aid in timing of harvest and site preparation)?
  • Is the seedbed suitable for germination or is site preparation needed?
  • What conditions are suitable for growth once established (shade tolerance)?
  • Are further treatments required and available to get stock to meet free growing requirements? If so, what and when?

List the potential risks that should be analyzed at this stage.

  • windthrow
  • forest health (insects, disease, animals)
  • visual quality
  • recreational values
  • fire hazard
  • regeneration
  • habitat values
  • biodiversity
  • timber quality