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FOREST SERVICE HANDBOOK
PORTLAND, OREGON
2409.26c - TIMBER STAND IMPROVEMENT HANDBOOK
R-6 Amendment No. 2409.26c-93-2
Effective May 13, 1993
POSTING NOTICE. Amendments to this handbook are numbered consecutively.
Check the last transmittal sheet received for this handbook to see that the above
amendment number is in sequence. If not, obtain intervening amendment(s) at
once from the Information Center. Do not post this supplement until the missing
one(s) is received and posted. After posting, place the transmittal at the front of the
title and retain until the first transmittal of the next calendar year is received.
The last Amendment to this handbook was 2409.26c-93-1 (!2409.26c
Contents).
Document Name
Superseded New
(Number of Sheets)
2409.26c,40
Digest:
Chapter 40 - New Chapter, updates pruning for wood quality processes.
JOHN E. LOWE
Regional Forester
10
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FSH 2409.26c - TIMBER STAND IMPROVEMENT HANDBOOK
R-6 AMENDMENT 2409.26c-93-2
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CHAPTER 40 - PRUNING
41
INTRODUCTION
41.
1Objectives of Pruning
42
PRETREATMENT EVALUATION
42.
42.2
1Acceptable Stand Types and Management Areas
Analysis of Potential Gain in Clear Wood Volume and Increased Value
43
PROJECT PLANNING
43.1
43.2
43.3
43.31
43.32
43.33
43.4
Environmental Analysis
Silvicultural Prescription
Interdisciplinary Coordination
Fire Management
Wildlife
Pest Management
Implementation of Project Plans
44
TREATMENT METHODS
44.1
44.2
44.3
Hand Saws
Power Saws
Powered Pruning Equipment
45
MONITORING
45.1
45.2
45.3
Objectives
Operational Monitoring
Post-Project Monitoring
46
RECORDS AND REPORTS
47
AVAILABLE RESOURCES
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41 - INTRODUCTION. This chapter provides guidelines for the use of pruning as a
timber stand improvement treatment.
Identification of specific methods,
techniques, and priorities is left to Forest supplementation. Pruning may be
defined as removal of limbs on the lower portion of a tree.
41.1 - Objectives of Pruning. The primary objectives of pruning are to increase the
clear wood volume of a tree when harvested, and disease control. Other objectives
may include wildlife habitat improvement and aesthetics.
42 - PRETREATMENT EVALUATION. An analysis should be completed to
determine the need for pruning, predict the expected financial return and outcome
in increased clear wood volume, effective disease control, and so forth. The analysis
should include the effect of pruning on nontimber values and assess possible
beneficial and adverse impacts from the activity. An evaluation does not have to be
done for all pruning projects but should be done when first considering a project, or
when factors affecting the analysis significantly change. The following is the
recommended process for evaluating a pruning project.
42.1 - Acceptable Stand Types and Management Areas. Pruning should be
considered only in stand types where documented research indicates a positive
return on investment, or where substantial resource benefits from disease control
can be demonstrated, for example, control of dwarf mistletoe, white pine blister
rust, and western gall rust.
1. Acceptable Species. Douglas-fir and ponderosa pine have had sufficient
analysis on an operational and research basis to warrant investment within Region
6. Other species may be considered if a justification of a pruning investment can be
made, such as pruning western white pine for blister rust control, or integrating
pruning of trees for bough collection or other special forest products. Species which
exhibit significant epicormic branching should not be considered for operational
pruning.
2. Acceptable Management Areas. Forest Plans outline the management
objectives for each management type within the Forest. The silvicultural regimes
for these areas will determine the appropriateness of pruning. For example,
management areas which would not allow the removal of pruned trees in sufficient
number (that is, areas allowing salvage type operations only) or areas requiring
long rotations well past financial maturity of a pruning investment may not be
compatible with pruning. However, such constraints should not preclude the option
of further analysis. Possibilities, such as removing pruned trees in a thinning
within the long rotation areas, may be feasible.
42.2 - Analysis of Potential Gain in Clear Wood Volume and Increased Value. The
following are recommended steps in determining the wood quality gain from
pruning. Steps 1 through 3 identify assumptions which need to be addressed and
step 4 identifies a method to analyze pruning operations which incorporate the
latest research in pruning recovery.
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1. Pruning Height. To determine the length of the bole to be pruned, the
following factors should be considered:
a. Projected log length standards at time of harvest. To help assure the
highest value from the clear wood produced, pruning lengths should
accommodate the most likely log lengths marketable at time of harvest.
b. Relation of pruning costs with pruning height. Considering the
available pruning tools, what are the incremental costs of increasing the
pruning height?
c. Number of pruning entries. If the final pruned log length is 20 feet, one
alternative may be to prune once to approximately 10 feet (considering percent
of live crown) when the stand is younger with a smaller diameter, then
pruning the additional 10 feet at a later entry (pruning in two lifts). The other
alternative would be to prune once to 20 feet at the older age.
2. Stand Entry Criteria. Consider the following factors when determining
the optimum time in stand development to prune:
a. Pruned log size and pruning's impact on tree growth. To produce the
most clear wood at time of harvest, trees should be pruned at the youngest
possible age without significantly affecting growth. This may be accomplished
by pruning a tree to the desired height by removing dead limbs on the lower
portion of the bole and live limbs on the lower live crown, which are not
significantly contributing to stem growth. A review of Douglas-fir pruning
trials conducted by O'Hara (1991) indicates it is likely one third of the live
crown may be removed from a young Douglas-fir tree without significantly
affecting growth. However, considering the one-third live crown removal
without relating it to the trees pretreatment live crown ratio, may result in
considerably different growth response due to the pruning. If using the onethird rule and assuming the desired pruning height was 18 feet, one option
would be to prune when the tree has reached a height of 42 feet and the crown
has receded 6 feet off the ground, leaving a 36-foot live crown. Pruning to 18
feet would cut 12 feet into the live crown, removing approximately one-third of
the crown. Pruning later, assuming further crown recession, could remove
only dead limbs and leave a larger knotty core. Another option, which will
result in a pruning height of 18 feet with a small knotty core, is to prune in
multiple lifts starting at the sapling stage. However, care must be taken in
early pruning to avoid removing enough live crown to cause slowed growth
which could affect crown position within the stand and growth potential before
harvest.
b. Pruned limb size. Pruning of limbs larger than 1 inch in diameter may
increase cost due to cutting difficulty; increase the potential for rot because of
the increased likelihood of heartwood; and take longer for the cut surface to
heal.
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c. Financial carrying cost of pruning in regard to the harvest age.
Pruning a stand later than suggested above to maximize clear wood volume
production may be preferred to reduce the length of time between pruning
investment and harvest. However, this will increase the size of the knotty core
and probably reduce the financial return. When possible, pruning for wood
quality should be evaluated in conjunction with special forest products
projects. This not only allows earlier pruning, but often times can be
incorporated as a requirement of the contract, and be accomplished at no
additional cost to the Government.
d. Timing with other silvicultural activities. Pruning after a commercial
or precommercial thinning may be preferred to assure only crop trees are
pruned, but may cause pruning difficulty because of thinning slash. Pruning
prior to commercial thinning will premark the stand for thinning, but pruned
trees may be damaged during the harvest operation. Pruning without
thinning may increase the potential for unpruned competitors to outgrow
pruned trees. Also, existing studies indicate higher financial returns from
pruning stands with quite low stocking.
e. Timing with consideration of possible disease, insect, and wildlife
impacts. Childs and Wright (1956) indicate pruning in the fall reduces the
potential for incidence of fungal infections in Douglas-fir, compared with
spring pruning, although in either case stem decay was insignificant.
3. Pruned trees per acre. Trees to be pruned should be capable of rapid
enough growth to produce an acceptable amount of clear wood at time of harvest.
Generally, the first priority for pruned tree selection is the larger, faster growing
trees in the stand that have the potential of providing the most clear wood and
greatest economic return. Prune tree selection may also be influenced by resource
needs, such as improving or enhancing wildlife habitat. The target trees per acre to
be pruned will depend on projected number of trees reaching final harvest and
projected growth rates of trees distributed throughout the various crown classes. A
small allowance for mortality may be necessary.
4. Project Value and Volume Gained from Pruning. Determining the
value and volume gained from pruning requires a number of financial and lumber
recovery assumptions. A list of publications found in subsection 47 contain some of
the more applicable studies and analysis procedures for Region 6. The Douglas-fir
"DF PRUNE Users Guide" (Fight, 1991) and ponderosa pine "PP PRUNE Users
Guide" (Bolon, 1991) simulators are recommended for projecting the value of
pruning Douglas-fir and ponderosa pine. The use of "Price Projections for Selected
Grades of Douglas-fir, Coast hem-fir, Inland hem-fir, and ponderosa pine lumber
(Haynes and Fight, 1992)" is recommended to estimate future lumber values needed
in the above simulators. "Production, Prices, Employment and Trade in Northwest
Forest Industries" (Res. Bull. Published quarterly) is recommended for current
lumber prices and past trends. The following data are also required in order to use
the simulators:
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a. Pruning and harvest age.
b. Diameter of potential pruned trees at time of pruning and harvest.
c. Height of potential pruned trees at time of pruning and harvest.
d. Limb diameter. (An estimation of the diameter of the largest limb on the
pruned portion of the bole, at time of pruning and final harvest. This, along
with the diameter breast height at age 20 is needed for the DF PRUNE
simulator only.)
e. Estimated pruning cost per tree.
It should be noted that current log grading rules for Douglas-fir and ponderosa pine
rely heavily on knots and knot indicators for determining grade and value. Due to
the nature of tree growth, knot indicators will remain on the bark surface even
though several inches of clear wood may exist below the indicator.
43 - PROJECT PLANNING. If the above analysis indicates pruning is a viable
treatment, specific areas may be identified to implement a project. The above
analysis procedure will help provide criteria for stand selection and pruning
specifications.
43.1 - Environmental Analysis. An Environmental Analysis (EA) should be
completed according to the National Environmental Policy Act (NEPA). NEPA
defines a process which provides for scoping and an interdisciplinary approach
which helps insure all resources are adequately considered and concerned publics
are involved. When an analysis and past experience indicate no significant effect
will occur, a categorical exclusion may be considered. Public sensitivity and other
local conditions may affect the choice of documentation required.
43.2 - Silvicultural Prescription. After an EA is prepared for a project, a
silvicultural prescription should be written displaying the preferred alternative.
The analysis and prescription shall include documentation for stand selection
criteria and operational specifications. Stand selection criteria shall include; (1)
stocking levels (lower stocked stands usually produce a greater return from pruning
because pruned trees have more room to grow and produce more clear wood), (2) site
index (higher sites will usually produce more clear wood volume per pruned tree),
(3) height to live crown, and (4) timing with other silvicultural activities, both
completed and planned.
Operational specifications should include; (1) pruning height, (2) tree selection
(specifications should designate the healthier, well formed trees, most likely to be
dominants and codominants at harvest time as pruned trees), (3) allowable live
crown removal or minimum live crown ratio following pruning, (4) allowable branch
stub length, (5) restrictions on stem damage, and (6) desired pruning equipment.
43.3 - Interdisciplinary Coordination.
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43.31 - Fire Management. Coordination with Fire Management is specified in WO
AMEND FSM 2476.4. It is recommended that fuels treatment needs be evaluated
on the basis of a risk analysis to determine the appropriate level of hazard
reduction required. In planning pruning projects, emphasis should be placed on
avoiding development of excessive hazards that would make adequate protection
impractical. Size, location, distribution of pruning units, scheduling of pruning or
slash disposal on nearby units, disposal plans, and protection facilities all have a
bearing on what may be an excessive hazard. It is unlikely that fuels created from
pruning alone would require treatment.
43.32 - Wildlife. Evaluate potential pruning impacts (positive and negative). For
example, pruning may encourage big game damage to the cambium of young trees,
and in areas with a history of this, pruning may not be advisable; or measures may
need to be taken to minimize potential damage.
43.33 - Pest Management. Evaluate the possible insect and disease impacts which
may occur in a pruned stand. Specifically, the potential effects of insects and
diseases entering trees through wounds, or their attraction to pruned trees, should
be addressed in the prescription. It should be noted at this time, there is no
documented evidence that this is a problem for Douglas-fir and ponderosa pine.
43.4 - Implementation of Project Plans. The successful implementation of a pruning
project should be evaluated on how well it met the objectives stated in the
prescription. Pruning may be completed by contract or force account labor, but
acceptable performance shall be of equal quality for both, as verified through
inspection and project specification compliance.
44 - TREATMENT METHODS.
44.1 - Hand Saws. Cutting limbs with hand saws is the most common method of
pruning in the Region. At present, it appears to be the most cost-effective method of
pruning trees to a height of 18-20 feet. A number of pruning saws are available
with extension poles.
44.2 - Power Saws. Chain saws are an effective method which could be used on the
lower portion of the bole, but care must be taken to prevent damage to the tree. If
considering the use of chain saws because of large limb size, reevaluate the
treatment priority of the age and size of trees to be pruned. Pole mounted power
saws and clippers are also available on the market, but have not found widespread
use in Forest pruning operations.
44.3 - Powered Pruning Equipment. A number of robot-type pruners have been
developed which self-propel up a tree while removing limbs. At present, they seem
to be in the developmental stage with little use at the operational level in the
United States.
45 - MONITORING. Monitoring is the systematic observation, measurement,
collection, recording, and evaluation of data to determine the effects of treatment.
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The monitoring plan developed at the time the prescription is prepared includes
general and specific items to be monitored and the time when the appropriate
monitoring is to be accomplished.
45.1 - Objectives. The success of the prescription implementation should be
demonstrated by the results of an effective monitoring program. Monitoring also
provides information to determine if retreatment is needed, and if results are
outside of prescription tolerances.
45.2 - Operational Monitoring.
Operational monitoring includes project
implementation and achievement of the short-term objectives of the prescription.
This phase of monitoring includes compliance with pruning specifications and
determining the degree to which resource objectives have been met. It primarily
occurs during, and immediately after, the actual pruning operation.
45.3 - Post-Project Monitoring. Post-project monitoring will determine whether or
not the stand is developing as projected and whether the long-term objectives of the
prescription are being met.
Post-project monitoring should address such items as:
1. Stand development. Are the pruned trees gaining as much clear wood as
predicted, and more importantly, are they maintaining dominance over unpruned
trees?
2. Problems with heal-over of cut limbs.
In pruning for wood quality or disease control, operational and post-project
monitoring will help provide information to assist in developing future prescriptions
for similar stands; provides information for updating of Forest and resource plans
through better definition of stand growth models; provides an opportunity to more
accurately predict the timing of future stand entries; and allows rescheduling when
necessary.
It is not feasible or necessary to conduct a thorough long-term monitoring of all
pruned stands. Sampling of different stands and treatment prescriptions provides a
more efficient method for evaluating performance.
The use of benchmark
prescriptions is the recommended method for sampling a variety of recurring stand
conditions.
Information gathered through monitoring shall be recorded and maintained for
future use.
46 - RECORDS AND REPORTS. As pruning needs are identified, enter the
acreages in the SILVA portion of the automated Timber Activity Control System
(TRACS) by productivity class, state, Forest, and Ranger District. These data are
essential for displaying funding needs to Congress.
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Maintaining accurate records is extremely important. The location of pruned
stands, volume of clear wood and accompanying value can be accurately estimated if
reliable records exist. Although destructive sampling of representative trees near
harvest time can determine the amount of clear wood, it would be more efficient to
combine this method with accurate records to provide the best data at harvest time.
As a minimum, records for pruned stands should include the number of pruned
trees per acre, average diameter of pruned trees at time of pruning, pruning height,
and the criteria for tree selection. Records should also include accurate maps of
pruned stand locations.
Reporting is a requirement and shall be timely and accurate. FSM 2496 contains
instructions for National reporting requirements. Refer to the Region 6 Guide to
Silvicultural Reporting for specific information on reporting attainment and
certification of timber stand improvement activities.
47 - AVAILABLE RESOURCES. Forests and Districts are encouraged to exchange
information, ideas, and methods for improving pruning practices. A large body of
literature exists on the subject of pruning, and has been incorporated into a
bibliography (O'Hara, 1989) containing over 1,100 references. This publication and
other selected publications are listed below:
Barrett, J.W.
1968. Pruning of Ponderosa Pine...effect on growth. USDA Forest Service.
Research Paper. PNW-68. 9 p.
Bolon, N. ,R.D. Fight and J.M. Cahill.
1992. PP PRUNE Users Guide. USDA Forest Service, Pacific Northwest
Research Station. General Technical Report PNW-GTR-289.
Cahill, James M.
1991. Lumber recovery from pruned young-growth ponderosa pine. Forest
Products Journal.
Cahill, J.M., T.A. Snellgrove and T.D. Fahey.
1988. Lumber and veneer recovery from pruned Douglas-fir. Forest Products
Journal 38(9):27-32.
Childs, T.W. and E. Wright.
1956. Pruning and occurrence of heart rot in young Douglas-fir. USDA Forest
Service. Pacific Northwest Research Station. Research Note No. 132. 5 p.
Fight, R.D., J.M. Cahill, and T.D. Fahey.
1992. DF PRUNE Users Guide (Revision of PRUNESIM). USDA Forest
Service. Pacific Northwest Research Station. General Technical Report.
PNW-GTR-300. 12 p.
Fight, R.D., J.M. Cahill, T.D. Fahey, and T.A. Snellgrove.
1988. A new look at pruning coast Douglas-fir. Western Journal of Applied
Forestry. 3(2)46-48.
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Haynes, R.W. and R.D. Fight.
1992. Price Projections for Selected Grades of Douglas-fir, Coast hem-fir,
inland hem-fir, and ponderosa pine lumber. USDA Forest Service. Pacific
Northwest Research Station. Research Paper PNW-RP-447.
Maguire, D.A., J.A. Kershaw, and D.A. Hann.
1991. Predicting effects of silvicultural regime on branch size and crown wood
core in Douglas-fir. (accepted by Forest Science).
O'Hara, K.L.
1989. Forest Pruning Bibliography. University of Washington, Stand
Management Cooperative/Institute of Forest Resources Contribution No. 67.
74 p.
O'Hara. K. L.
1991. A Biological Justification for Pruning in Coastal Douglas-Fir Stands.
Western Journal of Applied Forestry. 5p.
Shaw, E.W. and G.R. Staebler.
1950. Financial aspects of pruning. USDA Forest Service. Pacific Northwest
Research Station. 45p.
Staebler,G. R.
1963. Growth along the stems of full crowned Douglas-fir trees after pruning
to specified heights. Journal of Forestry. 61(2):124-127.
Stein, W.I.
1955. Pruning to different heights in young Douglas-fir. Journal of Forestry.
53:352-355.
Warren, Debra D.
Published quarterly. Production, prices, employment, and trade in Northwest
forest industries. Research Bulletin. USDA Forest Service, Pacific Northwest
Research Station.