2409.12_30
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FOREST SERVICE HANDBOOK
ALASKA REGION (REGION 10)
JUNEAU, ALASKA
FSH 2409.12 – TIMBER CRUISING HANDBOOK
CHAPTER 30 – CRUISING SYSTEMS
Supplement No.: R-10 2409.12-2006-6
Effective Date: July 24, 2006
Duration: This supplement is effective until superseded or removed.
Approved: /s/ Paul K. Brewster (for)
DENNIS E. BSCHOR
Regional Forester
Date Approved: 07/24/2006
Posting Instructions: Supplements are numbered consecutively by Handbook number and
calendar year. Post by document; remove the entire document and replace it with this
supplement. Retain this transmittal as the first page(s) of this document. The last R-10
Supplement to this Handbook was 2409.12-2006-5 to chapter 40.
New Document
2409.12_30
5 Pages
Superseded Document(s) by
Issuance Number and
Effective Date
2409.12_30 (2409.12-2004-4, 7/9/2004)
5 Pages
Digest:
30: Updates approved cruise methods to be used with residual value appraisals. Corrects
caption to read as Cruising Systems.
35: Corrects caption to read the same as the parent text.
R-10 SUPPLEMENT 2409.12-2006-6
EFFECTIVE DATE: 07/24/2006
DURATION: This supplement is effective until superseded or removed.
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FSH 2409.12 – TIMBER CRUISING HANDBOOK
CHAPTER 30 – CRUISING SYSTEMS
30 – CRUISING SYSTEMS
The following cruise methods are the only approved methods of cruising when timber sales are
to be appraised using residual value.
1. 100 Percent
2. Fixed Plots
3. Variable Plots
4. 3P Sampling*
5. Fall, Buck, and Scale
6. Sample Tree
7. PCMTRE*
* Use of these methods requires a great deal of caution. If the prescription changes after the
cruise it may necessitate a complete re-cruise of the sale.
Regardless of cruise method used or Silvicultural prescription, cruise and grade all trees,
including leave trees, to a minimum 9.0” DBH.
Record cut or leave trees as appropriate on the cruise tally sheet or data recorder.
34 - FIXED PLOTS
34.21 - Sample Plot Location and Monumentation of Plots and Trees
1. Correcting for Boundary Overlap.
In fixed-size plot sampling, if any part of a sample plot overlaps a boundary, biased estimates
will result from the plot unless the area of overlap is taken into account, or other suitable
alteration procedure is made. Use the Mirage method as described below and in 34.21 Exhibit
01 when fixed plots land so their boundary would overlap outside the sale area or into a different
cruise strata. As shown, measure the distance to the boundary, B, and establish a correction plot
center by going this distance beyond the boundary. Tally each tree in the shaded portion of the
exhibit twice in the sample.
R-10 SUPPLEMENT 2409.12-2006-6
EFFECTIVE DATE: 07/24/2006
DURATION: This supplement is effective until superseded or removed.
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FSH 2409.12 – TIMBER CRUISING HANDBOOK
CHAPTER 30 – CRUISING SYSTEMS
34.21 – Exhibit 01
Mirage Method When Used In Conjunction With Fixed Area Plots.
Do not tally a tree from a correction point unless it has first been tallied from the sample point.
Only trees inside the unit area are tallied.
The use of the mirage method is illustrated in 34.21 Exhibit 02. If the plot boundary overlaps
both sides, and completely overlaps the corner itself, a total of three correction plots are needed.
If the plot boundary overlaps both sides, but not the corner, establish two correction plot centers
D and D2. From each correction plot center tally those trees falling inside the cruise boundary.
Two sets of trees will be tallied twice. Note: When three correction plots are established (four
total plots), some trees will be tallied only once, some twice, some three times, and some four
times.
R-10 SUPPLEMENT 2409.12-2006-6
EFFECTIVE DATE: 07/24/2006
DURATION: This supplement is effective until superseded or removed.
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FSH 2409.12 – TIMBER CRUISING HANDBOOK
CHAPTER 30 – CRUISING SYSTEMS
34.21 – Exhibit 02
Mirage Method
35 - POINT SAMPLING
35.21 - Sample Point Location and Monumentation of Points and Trees
1. Correcting for Boundary Overlap.
If point sampling is used, although plot size varies with tree diameter, overlap is easily detected.
Overlap exists when the radius of the plot associated with the tree exceeds the distance B, from
the sample point to the boundary. This boundary overlap is a form of bias that can occur when
any part of a tree’s associated plot extends beyond the boundary of the forest tract (or forest
type) being sampled. In such a situation the probability of the sample point falling within this
associated plot is reduced, which, if not corrected, leads to a certain amount of bias. (See section
34.21.)
R-10 SUPPLEMENT 2409.12-2006-6
EFFECTIVE DATE: 07/24/2006
DURATION: This supplement is effective until superseded or removed.
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FSH 2409.12 – TIMBER CRUISING HANDBOOK
CHAPTER 30 – CRUISING SYSTEMS
To apply the mirage method in horizontal point sampling, one should follow these guidelines:
1. Establish plot.
2. Determine “in/out” trees on the unit side.
3. Measure distance and direction to boundary. Determine if overlap exists. This is the
case when the plot radius Ri associated with any qualifying tree exceeds the shortest (for
example, perpendicular) distance B from the sample point to the boundary. This can be readily
checked for the qualifying tree of the largest diameter Di. Thus if Ri>B, overlap exists, where Ri
= Horizontal Distance Multiplier * Di.
4. If overlap exists, measure the same distance and direction outside the boundary and
establish a temporary point (for example, mirage plot).
5. Determine “in/out” trees on the mirage side. Trees qualifying from this auxiliary
point are again tallied. Thus, some trees may be tallied twice, which represents the adjustment
for the original plots being undersized. Do not tally a tree from a correction point unless it has
first been tallied from the sample point. Only trees inside the unit area are tallied.
In point sampling field application, making use of the mirage method, one need not actually
determine whether overlap exists; it is only necessary to proceed the distance B from the
boundary, sight back toward the forested area with the angle gauge (for example: prism,
relascope, and so forth) and tally all qualifying trees from the correction point. Of course, if
overlap is present, certain trees will be the same ones tallied from the original sample point. If
there is no overlap, no trees will qualify from the correction point.