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FOREST SERVICE HANDBOOK
DENVER, CO
FSH 2409.26 - SILVICULTURAL PRACTICE HANDBOOK
Region 2 Amendment No. 2409.26-96-9
Effective June 29, 1996
POSTING NOTICE: Amendments are numbered consecutively by Handbook
number and calendar year. Post by document name. Remove entire document and
replace with this amendment. Retain this transmittal as the first page of this
document. The last amendment to this Handbook was Amendment 2409.26-96-8 to
2409.26,0 Code.
Document Name
2409.26,10
Superseded New
(Number of Pages)
--
Digest:
10 - This is a technical amendment to reformat chapter text.
ELIZABETH ESTILL
Regional Forester
9
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FSH 2409.26 - SILVICULTURAL PRACTICE HANDBOOK
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CHAPTER 10 - SILVICULTURAL SYSTEMS
10 - REQUIREMENTS FOR APPLICATION. Application of silvicultural practices
requires that:
1. There is reasonable assurance that stands can be amply restocked within 5
years after final harvest, unless openings are created to meet other resource
objectives, Forest Plans, or protection of adjacent stands is enhanced.
2. Stands have been identified as available, capable, and suitable for timber
production; or stands not suitable for timber production if management of
nontimber resources requires stand management within the scope of Forest Plans.
3. The biological net growth potential for the land equals or exceeds minimum
Regional standards of 20 cubic feet per acre per year, except as needed to protect
other multiple use values or accomplish other objectives within the scope of Forest
Plans.
4. Technology, including harvesting, site preparation, and regeneration, exists
that will assure timber production without significant or permanent impairment to
soils, productivity and watershed, or other resource values.
"Significant or permanent impairment," as used above, means that use of mitigation
and enhancement measures will not recapture resource values within a reasonable
time frame. "Impairment" should not be confused with "disturbance." Silvicultural
operation cannot be done without disturbance of resources, but they may be done
without impairment of resources.
10.1 - Summary. A summary of silvicultural systems and cutting methods is shown
in exhibit 01.
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10.1 - Exhibit 01
SEE THE PAPER COPY OF THE MASTER SET
FOR SECTION 10.1 - EXHIBIT 01.
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11 - CUTTING METHODS FOR EVEN-AGE SILVICULTURAL SYSTEM. The
even-age silvicultural system may be applied where managed even-aged forests
contain many stands that vary in age, and therefore in size of trees. Clearcutting,
shelterwood cutting, seed-tree cutting, intermediate cuttings and their many
variations are the cutting methods used in the even-age silvicultural system. The
step that initiates regeneration is generally made during the planning period when
culmination of mean annual increment of growth has occurred; however, even-aged
stands may require one or more intermediate entries for cultural work, commercial
thinnings, salvage, and sanitation. Region 2 guidelines for cultural work are not
included in this Handbook.
11.1 - Regeneration Methods. Three even-age regeneration methods are recognized.
1. Clearcutting. Clearcutting removes all trees from a stand, or portion of a
stand, in one regeneration entry. The objectives of using clearcutting methods are:
to create new even-aged stands, create openings within the forest to meet other
resource needs, or to protect adjacent stands from insects or diseases.
Regeneration of clearcut stands is done through planting, direct seeding, or site
preparation for naturals. Where the objective is to create a new stand, clearcutting
will be done only on areas where regeneration can be reasonably assured within 5
years. Site preparation for naturals or direct seeding must include backup plans for
planting unless local experience shows that there is reasonable assurance that
natural regeneration will occur. Clearcutting techniques include patch, stand, and
strip. Distinction between the techniques is primarily size and shape of the opening
in the tree canopy.
Patch cuts create small openings within a stand and shall not exceed ten acres in
size. Usually two or more patches are included in a stand. Small cutting units are
usually associated with high timber growing and logging costs.
Strip cuts are generally designed to be narrow openings that can be naturally
regenerated. Width of the strips should consider seed dissemination traits of the
desired species. Design for acceptable visual appearance and to permit
regeneration of future cuts is an important requirement for use of this technique.
Stand clearcuts are those in which the ensuing regeneration is recorded and
managed as a separate stand. Of the three clearcutting approaches, it is most
useful in Region 2. The major limitation is when stands are small, the
recordkeeping cost is high. Size normally will not be less than five acres, but any
small area may be managed as a stand if special or significant. As defined here,
many patch or strip cuts can be managed as stands. Maximum size of clearcuts is
limited to 40 acres unless approved by the Regional Forester.
2. Seed Tree Method. The objective of this method is to naturally regenerate a
new even-aged stand from a minimum number of trees reserved to provide a seed
source. To be successful the desired species must be intolerant, wind firm,
nonserotinous, and a reliable seed producer. The few trees retained for seed do not
provide a sheltered microclimate for seedlings. Normally less than 15 seed trees per
acre are retained with this method.
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There are usually two steps involved, the seed cut followed by a removal cut once
regeneration is established.
3. Shelterwood Method. The objective of this method is to create a new evenaged stand through natural regeneration. Enough of the old stand is retained to
proved both seed and a sheltered microclimate during the period of regeneration.
There are three steps to this method: preparatory cut, seed cut, and removal cut.
In many situations only the seed cut and removal cut are essential to successful
implementation of the method.
a. Preparatory Step. Recognized silvicultural objectives for this step
include developing windfirmness in leave trees, developing good seedbearing qualities of leave trees, or to accelerate breakdown of deep duff
layers. In stands that have had intermediate cuts or have reached old
age, this step often serves no silvicultural purpose.
In practice, this step is often prescribed to test windfirmness and not to
develop it. It is also often prescribed to avoid the appearance of sudden
changes in existing stand conditions. In the second situation it generally
turns out to be a seed cut followed by two or more removal cuts rather
than serving the purpose of a preparatory cut.
b. Seed Step. This cutting is the removal of trees in a mature stand so as
to effect permanent opening of its canopy and so provide conditions for
securing regeneration from the seed of trees retained for that purpose. In
addition, enough trees are retained to provide at least some modification
of the exposed microclimate that would result from clearcut or seed tree
methods. Normally, at least 15 leave trees per acre are retained but not
more than 60. Phenotypically desirable trees should be retained.
If high numbers of leave trees are retained during the seed cut, more
than one removal cut may be needed in order to prevent excessive
damage to the seedlings from logging the high volume in one operation.
c. Removal Step. All cuttings of mature trees after establishment of the
new stand are removal cuts. The objective of the removals is to provide
improved growing conditions for the new stand and to harvest remaining
mature trees. More than one removal can be scheduled for a stand.
Where manageable understories have resulted from fires or natural
disturbances, the removal cutting has been termed overstory removal or
simulated shelterwood cuts.
In stands where dwarf mistletoe is present in the mature trees, the
removal cut should be within 10 years of seedling establishment to
prevent heavy inflection of the new stand.
Careful administration of the logging operation for this step is needed to
prevent excessive damage to the young stand. Also, retention of
individual trees or groups of trees to meet multiple use objectives may be
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necessary. Size of the created opening shall be less than 40 acres unless
the young stand is more than 6 feet in height and visually significant.
11.2 - Intermediate Cutting Methods for Even-Age Silvicultural Systems.
Intermediate cutting methods are generally associated with tending of stands prior
to regeneration cuts.
1. Commercial Thinning. The objective of commercial thinning is to maintain
desirable rates of radical growth of individual trees while maintaining an
acceptable per acre rate of volume growth for the immature stand. To meet the
definition of commercial thinning, the majority of stemwood material from felled
trees must be sold and removed from the stand.
Appropriate stocking levels vary by cover type, site quality, and multiple use
objective. Stocking Guides will be given in the appendix of this Handbook as they
are developed.
Normally the largest and most phenotypically desirable trees are retained in the
stand, and damaged, diseased, intermediate, and suppressed trees are removed.
The basic approach is to thin from below, but there usually are scattered
overmature dominants, large limby (wolf) trees or damaged trees that will be
removed as well.
Retention of site occupancy by the existing stand is a goal of this treatment, so holes
in the stand or reduction of stocking to the point where a seedling understory
becomes established is not appropriate. Retention of a desired stocking level is
more important than leaving a stand of "perfect" trees.
2. Salvage. This method is used to harvest dead, dying or deteriorating trees
before their timber becomes worthless. The trees must be dead or their death
imminent. The method is usually applied to obtain utilization of material that
would otherwise be wasted, and consideration of regeneration or desired stocking
levels is not given much attention. Later treatments or harvests are generally
scheduled to bring the stand into a desired condition.
3. Sanitation. This method is used to harvest insect or disease infested trees
before death occurs. Prevention or control of spread of insects or disease may also
be an objective of this method. Sanitation cuts are often applied to young stands
infected with dwarf mistletoe to reduce the level of infection.
4. Precommercial Thinning. The objective for this method is similar to that for
commercial thinning but the trees felled are not utilized. The costs are usually
considered an investment to be charged against future stand values.
It includes incidental disease control work. Appropriate stocking levels are given in
Chapter 20.
5. Release/Weeding. The objective of this treatment is to free the desired crop
trees from competition with other vegetation. Weeding usually means felling or
killing of undesirable tree species while release is often construed to mean felling or
killing of desirable tree species to release the designated crop trees. Killing of brush
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or nontree vegetation is also considered release. The method includes incidental
disease control work.
The end result of this treatment is less competition for the future crop, but a
specified stocking level is not usually specified or accomplished. Followup
treatment for precommercial or commercial thinning is usually needed.
12 - CUTTING METHODS FOR UNEVEN-AGE SILVICULTURAL SYSTEMS.
Managed uneven-aged forests may take several forms depending upon the cutting
methods used. In some cases, the forest is similar throughout with individual trees
of many ages and sizes growing in close association. In other cases, small groups of
trees of similar age may be mixed with similar groups of different ages. Even
though the groups are even-aged, they are not referred to as even-aged stands.
Uneven-aged forests and stands may also contain several age classes on the same
area, creating a storied condition. Under uneven-age silviculture, regeneration is
obtained several or many times during the period required to grow an individual
tree, or group of trees, to maturity.
Single-tree selection and group selection cutting methods are used to harvest trees
and obtain regeneration. Intermediate harvests may be used between regeneration
harvests. Selection cutting is usually regulated by specifying the number of trees of
particular diameter classes (ages) to retain within each area to maintain a planned
distribution. Every size (age) class is treated in each entry. Scheduling harvest by
area or compartment is also used for this purpose. There must be reasonable
assurance that regeneration will follow within 5 years after the application of
selection cutting methods, unless: (1) openings are created to meet other resource
objectives; or (2) management of other resources dictates a longer regeneration
period.
12.1 - Regeneration Methods. Two uneven-age regeneration methods are
recognized.
1. Single-Tree Selection Method. This cutting method is applicable to stands
and forests where uneven-aged stocking conditions are desired. Stands are most
often identified by composition, geographic, or physical features. This cutting
method can be used to meet many land and resource objectives. However, if these
objectives are contrary to development of a specified distribution of diameter (age)
classes, some other cutting method must be used.
This cutting method is difficult to use, primarily due to regeneration constraints
and regulation of diameter (age) classes. In theory, natural regeneration should
follow removal of individual trees. Since natural regeneration generally requires
site preparation, and it is not practical to mechanically site prepare every spot
previously occupied by large trees, success may be limited for many species. Some
species are successfully regenerated when tree removal is followed by heavy seed
crops and a wet spring season, but such combinations are rare. Where natural
regeneration is successful, the stand or forest will move toward a climax state of
succession.
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If the species are affected by dwarf mistletoe, use of this cutting method will
increase the intensity of the infection. Seedlings cannot be protected unless the
source of infection is removed or a nonhost species is regenerated.
2. Group Selection Cutting Method. This cutting method is applicable where
grouped arrangements of trees exist or where they are desired. Groups vary in size
from a fraction of an acre up to two acres. Usually several groups are contained
within a stand. Stands are most often identified by composition, group clusters,
decadence, geographic or physical features.
This cutting method can be used to meet many land and resource management
objectives that involve uneven-age silvicultural management. However, if these
objectives are contrary to regeneration requirements or efforts to develop an even
distribution of diameter classes, clearcut methods must be used.
Groups are treated individually. They are clearcut at or near the time that
culmination of mean annual increment occurs. Earlier or later cutting can be done
to establish an even distribution of diameter classes by groups. Where groups are
not clearcut, but individual trees are commercially harvested, the single tree
selection or one of the intermediate cutting methods is used.
Where new groups are to be created by natural regeneration, the stand or forest will
move toward a climax state of succession. New groups of trees are often subject to
dwarf mistletoe infection. Protection of regeneration in openings created by
previous entry is a factor to consider in sale layout, transportation systems, and
logging.
One of the most difficult tasks of the silviculturist is to identify and describe cut
groups to sale layout people and markers. Indentifying cut groups should be done
with the basic concept of a specified distribution of diameter classes to create or
maintain a regulated condition. Intensive stand examination is required to do this
job right. Some groups are easily identified by their composition, structure, density,
or condition of health, but others are not and must be arbitrarily created. Control of
stand density within the groups not clearcut must also be done if groups are not
progressing satisfactorily towards a regulated condition.
12.2 - Intermediate Cutting Methods for Uneven-Age Silvicultural Systems.
Generally, treatment of younger trees and the regeneration cutting are
accomplished in each selection cut entry. Control of growing stock in size classes
too small to be treated by timber sales must be done in precommercial treatments.
Release/Weeding. Release and/or weeding should be considered after each selection
harvest to obtain the desired stand structure in submerchantable size classes, to
exert some control on species composition and to fell small trees that have been
badly damaged by the logging.
The treatment can be costly and difficult to administer and consequently is seldom
used when needed. The neglect of the submerchantable size classes has a
cumulative effect, and not obtaining the ingrowth needed to sustain productivity of
the stand has been a major factor in experienced poor results from selection cutting.
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13 - SPECIAL CUTTING. Any cutting methods that are used in even-aged or
uneven-aged stands which do not agree with the definitions, implementation, and
objectives as stated in this Handbook are considered not to be related to a
silvicultural system. Such cutting methods are referred to as "special."
This cutting method is used to improve or maintain some special quality of
resources. Use may or may not include regeneration, improved net growth or
residual trees, or other values to timber management, but this may occur anyway.
Objectives must be stated in a manner that can be measured and evaluated as to
success or failure--quantity, quality, and time frames involved. Use of the special
cutting methods will be minimal because most resource management objectives can
be accomplished using other cutting methods.
14 - SILVICULTURAL PRESCRIPTION AN THE FOREST PLANS. Forest Plans
contain prescriptions that indicate silvicultural procedures for various cover types
and management areas. To successfully implement prescriptions within these
plans, it is necessary to understand what the figures in the plan represent and how
they were obtained.
Common to all plans in Region 2 is some kind of sample of forest conditions. These
samples were then grouped into classes of roughly similar characteristics and an
average stand calculated for the grouped plots. The groupings are roughly
equivalent to timber types in old timber management plans, but a little more
generalized. These were modeled as Condition Classes in most FORPLAN
simulations using a treatment appropriate to the average condition. An average
age is assigned to each Condition Class in FORPLAN.
It must be remembered that the prescription thus designed for the average
condition and age cannot fit every stand represented by the condition class. This is
because poorly stocked stands may be average with well stocked, young with old,
good site with poor site. For example, to actually produce the outputs called for by
the plan, the young stand that grew well enough to be in sawtimber size class
should be commercially thinned or not treated even though the prescription in the
Forest Plan may show seed cut for the sawtimber stand condition.
When a stocking level is specified in a Forest Plan it is for an average condition on
an average site modeled as though it were a single stand. If the forest is to perform
as it is simulated in FORPLAN, the stands on average sites should be thinned to
the specified stocking, but poor sites should be at lower and good sites at higher
stocking levels.
In other words, a Forest Plan based on simulating the effect of commercial thinning
to a moderate stocking level, is not based on simulating every stand to exactly the
growing stock level specified for the average condition.