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Silviculture
An Envirothon Primer Glenn ³Dode´ Gladders
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What is Silviculture?
Silviculture is the application of the
principles of forest ecology to a stand of
trees to help meet specified objectives.
Objectives can include income, wildlife
habitat, water quality, recreation, or any
other values a forest is capable of providing.
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The Big Picture
If you understand one basic idea, you canunderstand almost everything else in
forestry.
This idea is shade tolerance as it pertains to forest succession!
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Tolerance
Different species of trees have differing
abilities to tolerate extended periods under
a closed canopy.
Species are generally divided into tolerant,
intolerant, and intermediate categories.
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Intolerant Species
Intolerant species are
generally the ³first in´
after an event such as
a clear-cut or a major
fire that substantially
opens the canopy.
These trees are oftencalled pioneer species.
These trees tend to:
- be fast growing
- be short-lived - have light seeds
Sweetgum leaf
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Tolerant Species
These trees normallyare not the first tocolonize open areas.
Instead, they grow upinto an existingcanopy.
Usually, these treesare found in the³climax community.´
These trees tend to:
- live a long time
- grow slowly- have heavier seeds
Beech nut
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Intermediate SpeciesAs the name implies, these trees have
characteristics that are ³in between´ the tolerants
and the intolerants.
Eastern white pine
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Example 1: Pacific NorthwestIntolerant Pioneers
red alder
bigleaf maple
Douglas-fir
Tolerant
Climax
Community
western
hemlock
western
redcedar sitka spruce
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Example 2: New EnglandIntolerant Pioneers
red maple
quaking aspen
yellow birch
Tolerant
Climax
Community
American
beech
sugar maple
easternhemlock
spruces
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Delaware
Intolerant Pioneers
red maple
yellow-poplar
sweetgum
loblolly pine
Tolerant Climax
Community
American beech
some oaks
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Succession
The change in species composition that occurs in a stand
over time.
An area is colonized by intolerant, fast-growing species.
Eventually, tolerant trees become established in theunderstory and start growing into the canopy.
One of two things then happens. Either (1) the intolerants
die naturally and are replaced by the tolerants that have
been present in the understory for some time, or (2) thetolerant trees finally overtop the intolerants and shade them
out, causing them to die.
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Disturbance
Events such as landslides, fires, clear-cuts, floods,
etc. that clear an area of vegetation, allowing light
to reach the ground.Can be natural or man-made
A disturbance can re-start forest succession from
scratch.
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Even-aged vs. Uneven-aged
ManagementYour management goals and the shade tolerancesof the species involved will determine whether tomanage on an even-aged or uneven-aged basis.
A Rule of Thumb:
For intolerant species, even-aged management is best.
Use uneven-aged management for tolerantspecies.
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Even-aged Management ± Shade
Intolerant Species1. Even-aged systems
The goal here is to
remove enough of thecanopy to allowintolerant species toregenerate.
Used for intolerantspecies only.
All trees in the standare the same age.
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Even-aged Management
The age at which a stand is harvested is
called the rotation age.
Normally, standing trees are
converted into logs,
And the site is regenerated
with the next crop of trees.
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Even-aged Management ± Shade
Intolerant Species
Even-aged management options include:
1. Clear-cutting: Remove all trees
2. Seed tree systems: leave just a few trees per acre
3. Shelterwood systems: leave 20+ trees per acre
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Even-aged Management:
Cl ear-cutting
All trees are cut, leaving a large open space
with full sunlight for new seedlings.
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Even-aged Management:
Cl ear-cutting
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Even-aged Management:
S eed Tree
The seed tree harvestunit acts as a clearcut, but with naturalregeneration from
trees in the originalstand.
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Even-aged Management:
Shel terwood
20 or more trees per acre are left on site to provide some shelter for seedlings for thefirst few years.
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Even-aged Management:
Shel terwood
This stand has been opened up sufficiently for sunlight
to reach the forest floor for the entire day.
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Uneven-aged Management ±
ShadeT
olerant Species1. Uneven-aged systems
The goal is to remove only enough of
the canopy to allow shade-tolerant speciesto regenerate.
Used for shade tolerant species only.
Multiple age classes.
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Uneven-aged Management ±
ShadeT
olerant Species
Uneven-aged management options include:
1. Group selection systems: small areas are
harvested.
2. Single tree selection systems: individual
trees are harvested.
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Uneven-aged Management:
G
roupS
el
ectionGroup selection harvests are basically small clear-
cuts, with the diameter of the opening less than
twice the height of dominant trees in theadjacent stand.
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Uneven-aged Management:
G
roupS
el
ection
As the day progresses, different portions of the harvest unit receivesun and shade.
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Uneven-aged Management:
S
ing l
e TreeS
el
ection
As the name implies, single trees are removed.
This creates only small gaps with minimal
additional light reaching ground level.
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Uneven-aged Management:
S
ing l
e TreeS
el
ection
This technique favors the very shade-tolerant
species.
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Uneven-aged Management:
S
ing l
e TreeS
el
ection
Note how the understory remains dark even after
the harvest.
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H
ow do we DO
silviculture?1. Determine your goals for your forest.
2. Evaluate existing conditions in the forest.
3. Decide what treatments, if any, can helpyou reach your goals.
4. Implement treatments at the right time.
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Treatments - Planting
Genetically superior tree seedlings are
available from commercial nurseries for
most commercial and wildlife species.
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Treatments - Thinning
Why thin?
Thinning opens a dense stand, resulting in larger
crowns (more leaves).
This translates to greater diameter growth and
earlier marketability.
Thinning can also improve forest health and
reduce fire hazards.
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Treatments - Thinning
Pre-commercial thinning (young stand)
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Treatments - Thinning
Commercial thinning (older stand)
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Treatments - Pruning
Pruning is done
primarily with pinesand other conifers. It
creates a high-quality,
knot-free butt log with
minimal taper.
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Treatments - Burning
Burning periodically can reduce unwanted
competition in some places.
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Treatments - Fertilization
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Treatments ± Returning to
Age Zero
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A Question for Future Foresters
Most of the wood and paper we use in this
country come from loblolly pine andDouglas-fir. These two species are
intolerant of shade.
W
hat does this imply in terms of how wemanage for these two species?