EFFECTIVE DATE: 09/10/2010
DURATION: This supplement is effective until superseded or removed. / 2409.12_30
Page 1 of 7
FSH 2409.12 – TIMBER CRUISING HANDBOOK
Chapter 30 – cruising systems
/ Forest Service Handbook
northern region (region 1)
missoula, mt
fsH 2409.12 – TIMBER CRUISING HANDBOOK
chapteR 30 – cruising systems
Supplement No.: 2409.12-2010-2
Effective Date: September 10, 2010
Duration: This supplement is effective until superseded or removed.
Approved: LESLIE A. C. WELDONRegional Forester / Date Approved: 09/08/2010
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 2409.12-2010-1 to Chapter 10.
New Document(s): / 2409.12_30 / 7PagesSuperseded Document(s) by
Issuance Number and Effective Date / 2409.12-97-3 (07/21/1997) / 6Pages
Digest:
33– Removes the requirement to paint a continuous band around the tree at eye level. It is now replaced with the requirement that paint must be visible on all side of the tree. Paint will be applied to the tree at or above eye level, with heights normally ranging between DBH to 6 feet or more above the surface of the ground.
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:
- Paint must be visible on all side of the tree. Paint will be applied to the tree at or above eye level, with heights normally ranging between DBH to 6 feet or more above the surface of the ground.
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 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 34.21 - Exhibit 01 twice in the sample.
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 no 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.
34.21 - 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.
34.21 – Exhibit 02
Mirage Method
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 of this handbook.
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.
36.2 - Field Procedures. Mark 3P sample trees as described in section 33.11.
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.
Given:
Multistage fixed plot cruise.
Presale measurement sale, conifer 3.5 MMBF (7000 Ccf) 20 percent.
3P CV is 25 percent.
Plot CV is 65 percent.
Range of 3P errors.
t = 2 for 95% probability.
1. Determine the desired sampling error for the sale as a whole, for this example assume 20 percent based on a "t" value of two.
2. 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. In this example the 3P error was estimated at 8 percent. 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 / 9.0Step 3 / Number of 3P Sample Trees / 51 / 44 / 39 / 35 / 31
Step 4 / Plot Error / 18.7 / 18.5 / 18.3 / 18.1 / 17.9
Step 5 / Number of Plots / 48 / 49 / 50 / 52 / 53
3. Calculate the number of 3P samples needed to meet the estimated 3P error, then repeat this step for the other increments of 3P error. Display the number of samples below the corresponding error. Sample calculations are shown for a 3P error of 8.0 percent and CV of 25 percent.
4. 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:
5. 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.
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.
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