Where does commercial thinning fit?
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.
How well do you know your silvicultural systems?
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)
Persistent leave-trees
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.
Criteria for leave-trees
Determining the number of leave-trees in seed tree and shelterwood systems
The number and distribution of leave-trees in seed tree and shelterwood systems depends upon:
Determining the number of leave-trees in seed tree and shelterwood systems
The number and distribution of leave-trees in seed tree and shelterwood systems depends upon:
A sprouting concern
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.
Grouped seed tree versus uniform seed tree
Group versus uniform shelterwood systems
Applying a nurse-tree shelterwood
Can you think of some suitable stand types for a nurse-tree shelterwood?
Size of group openings - Group selection systems
Compare group shelterwood to group selection
Do you understand the difference between group selection and group shelterwoods? Study the following diagram and describe the differences.
Species selection
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.
Stand structural changes over time - The impact of reserves
Key points
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.
Silvical questions for natural regeneration
List the silvical questions we would have to ask before deciding on natural regeneration:
Potential risks
List the potential risks that should be analyzed at this stage.