2409.12_30
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FOREST SERVICE HANDBOOK
SOUTHWESTERN REGION (R3)
ALBUQUERQUE, NM
FSH 2409.12 – TIMBER CRUISING HANDBOOK
CHAPTER 30 – CRUISING SYSTEMS
Supplement No.: r3_2409.12-2004-3
Effective Date: October 27, 2005
Duration: This supplement is effective until superseded or removed.
Approved: Abel M. Camarena for
Regional Forester
Date Approved:
September 27,2004
Posting Instructions: Supplements are numbered consecutively by Handbook number and
calendar year. Post by document; remove entire document and replace it with this supplement.
Retain this transmittal as the first page(s) of this document. The last supplement to this
Handbook was 2409.12-2004-2 to 2409.12_20.
New Document(s):
2409.12,30
6 Pages
Superseded Document(s) by
Issuance Number and
Effective Date
2409.12_30 (supplement 2409.12-96-3, 12/09/96) 6 Pages
Digest:
30 – This is a technical supplement that converts the format and style of this chapter to the new
FSH template using the agency’s current corporate word processing software. Although some
minor typographical and technical errors have been corrected, this supplement contains no
changes to the substantive direction in this chapter.
The direction included in this chapter has been developed through the coordinated efforts of
Regions 1, 2, 3, and 4. This coordination was initiated by the leadership of each Region under
the concept of shared services. All four Regions must concur on future changes to this direction.
R3 SUPPLEMENT 2409.12-2004-3
EFFECTIVE DATE: October 27,2004
DURATION: This supplement is effective until superseded or removed.
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FSH 2409.12 – TIMBER CRUISING HANDBOOK
CHAPTER 30 – CRUISING SYSTEMS
33 – SAMPLE-TREE WITH COMPLETE TALLY
33.11 – Operational Features
Mark sample trees in the following manner to help with sample location and identification during
presale inspection or check-cruises:
1. Paint a continuous band around the tree at about eye level.
2. Paint the sample number legibly.
3. Paint the cruiser ID legibly.
4. Identify with flagging.
Sample tree cruising often includes breaking individual species into sampling strata based on
DBH-groups. Expect that some trees measured as samples may have a DBH just slightly
different from the estimate made when the tree was tallied, and just outside the strata limit.
When this happens use the following procedure to maintain the random and unbiased nature of
the sample process:
In all cases, keep a sample tree in the strata it was originally called in. Do not skip
the tree or make other adjustments when it's taped DBH is outside the strata limits.
These trees represent other tallied trees that may have been called outside their "true"
DBH-group. Their effect will be to increase strata CV, usually by a very slight
amount. If a follow-up crew will be measuring the samples, be sure to mark the
sample trees in a way that indicates their "called" strata.
34.21 – Sample Plot Location and Monumentation of Plots and Trees
1. Identify plot centers with a firmly implanted solid stake. Do not use a wire pin.
Indicate the plot center by marking the top of the stake with an indelible "X" or a nail. Use a
grid system based on a random start to locate plot centers on the cruise map.
2. Use the Mirage method as described below and in exhibit 01 when fixed plots land so
their boundary would overlap outside the sale area or into a different cruise stratum. 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 exhibit 01 twice in the
sample.
R3 SUPPLEMENT 2409.12-2004-3
EFFECTIVE DATE: October 27,2004
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
If point sampling is used, although plot size varies with tree diameter, overlap is easily detected;
it exists when the radius of the plot associated with the tree exceeds the distance B, from the
sample point to the boundary. 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 out from the boundary, sight back toward the forested area with the angle gauge
(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.
Do not tally a tree from a correction point unless it has first been tallied from the sample point.
Only trees inside the unit are tallied from the correction point.
Exhibit 02 illustrates the use of the mirage method. If the plot boundary overlaps both sides, and
also 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 area 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.
R3 SUPPLEMENT 2409.12-2004-3
EFFECTIVE DATE: October 27,2004
DURATION: This supplement is effective until superseded or removed.
2409.12_30
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FSH 2409.12 – TIMBER CRUISING HANDBOOK
CHAPTER 30 – CRUISING SYSTEMS
34.21 - Exhibit 02
Mirage Method
SEE THE PAPER COPY OF THE MASTER SET
FOR SECTION 34.21 - EXHIBIT 02.
O = Sample point
X = Correction point
D = Distance from boundary to
sample point or correction
point
D2 = Distance from boundary to
sample point or second
correction point
D3 = Distance from boundary to
sample point or third
correction point
34.22 – Establishing Plot Boundaries
Use the slope corrections factors shown in section 91, exhibit 02, regional supplement.
35.21 – Sample Point Location and Monumentation of Points and Trees
Establish map locations and monument point centers in the same fashion as described for plot
centers in section 34.21.
Use the Mirage method as described in section 34.21.
35.22a - Assessing Borderline and Other Questionable Trees
The parent text prescribes measuring limiting distance to the face of the tree. Data recorder
routines for limiting distance are based on this measurement, not on the distance to the tree
center. Section 91, exhibit 02 (regional supplement) provides tables of factors to use in hand
calculations for limiting distance.
R3 SUPPLEMENT 2409.12-2004-3
EFFECTIVE DATE: October 27,2004
DURATION: This supplement is effective until superseded or removed.
2409.12_30
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FSH 2409.12 – TIMBER CRUISING HANDBOOK
CHAPTER 30 – CRUISING SYSTEMS
37.24 - Calculating Sample Size
The following section provides a guide for determining the number of samples needed for the
Fixed-Area Plot with 3P Subsample Cruising Method. The process involves two basic steps:
1. Based on precruise data, build an array showing a practical range of combinations for
fixed-plots versus 3P sample trees.
2. Select the most efficient combination based on cruising costs and other factors.
The following example illustrates the specific steps and calculations.
1. Given:
a. Presale measurement sale, conifer 3.5 MMBF (7000 Ccf), targeted sampling error
of 20 percent.
b. Estimated 3P CV is 25 percent.
c. Estimated 3P sampling error of 8 percent.
d. Estimated plot CV is 65 percent.
e. t = 2 for 95% probability.
2. Determine the desired sampling error for the sale as a whole.
3. Estimate the error for one of the sampling methods. 3P error is generally the more
easily estimated of the two errors. Use data from past cruises to estimate the 3P error and CV.
Display the error in the first row of an array, along with several increments above and below the
estimated error.
STEP-2
3P ERROR
7.0
7.5
8.0
8.5
9.0
STEP-3
51
44
39
35
31
STEP-4
NUMBER OF 3P
SAMPLE TREES
PLOT ERROR
18.7
18.5
18.3
18.1
17.9
STEP-5
NUMBER OF PLOTS
48
49
50
52
53
4. Calculate the number of 3P samples needed to meet the estimated 3P error, and then
repeat this step for the other increments of 3P error. Display the number of samples below the
corresponding error.
R3 SUPPLEMENT 2409.12-2004-3
EFFECTIVE DATE: October 27,2004
DURATION: This supplement is effective until superseded or removed.
2409.12_30
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FSH 2409.12 – TIMBER CRUISING HANDBOOK
CHAPTER 30 – CRUISING SYSTEMS
(t ) 2 (CV ) 2 (2) 2 (25) 2

 39
E2
8.0 2
5. Use the sale sampling error and estimated 3P error to calculate the fixed plot error.
Sample calculations for the mid-point 3P error are shown below:
3P Sample Trees  n 
Plot Error  ( Sale Error ) 2  (3P Error ) 2  (20.0) 2  (8.0) 2  336  18.3
6. Use past cruise data or reconnaissance information to estimate the CV for the plot
samples. Calculate the number of plots needed for each plot error shown in the array.
Fixed Plots  n 
(t ) 2 (CV ) 2 (2) 2 (65) 2

 50
E2
(18.3) 2
37.43 - Calculating Sample Size
The example in the parent text is for t = 1. The following example illustrates how to determine
sample size for t = 2, which is the standard for tree measurement sales. Definitions for the
variables include:
n = total samples (count points plus measure points)
k = measure points
CV = coefficient of variation for volume/basal-area ratio (V-bar)
E = sale sampling error
r = ratio of cost of measuring a point to the cost of counting a point.
Step 1: Determine the ratio for the cost of measuring a point divided by the cost of counting the
point, and the value for estimated CV and target sale sampling error. Values for the example are:
CV = 60 percent
E = 10 percent
r = 1.33
Step 2: Calculate the number of count points, k.
Number of count points  k 
(t ) 2 (CV ) 2  (0.433

 (2) 2 (60) 2  0.433

0
.
25
 0.25   90



2
2 
E
(10.0)  1.33
r



Step 3: Calculate the total number of points, n.
Total number of points  n  k (1.732) r  (90)(1.732)( 1.33 )  179.76  180 points