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2409.12_80.doc - USDA Forest Service

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2409.12_80.doc - USDA Forest Service

     2409.12_80 Page 1 of 18

     FOREST SERVICE HANDBOOK

    NATIONAL HEADQUARTERS (WO)

    WASHINGTON, DC

    FSH 2409.12 TIMBER CRUISING HANDBOOK

    CHAPTER 80 WEIGHT FACTOR DETERMINATION

Amendment No.: 2409.12-2008-1

Effective Date: July 23, 2008

Duration: This amendment is effective until superseded or removed.

Approved: CHARLES L. MYERS Date Approved: 07/15/2008

     Associate Deputy Chief, NFS

    Posting Instructions: Amendments are numbered consecutively by handbook number and calendar year. Post by document; remove the entire document and replace it with this amendment. Retain this transmittal as the first page(s) of this document. The last amendment to

    this handbook was 2409.12-2004-1 to 2409.12_70.

    2409.12_80 18 Pages New Document

    80 thru 81.2--3 4 Pages Superseded Document(s) by

    (Amendment 2409.12-93-1, 02/23/1993) Issuance Number and

    Effective Date

Digest:

    80 Changes chapter title from “Miscellaneous Timber Cruising Subjects” to “Weight Factor Determination.” Revises the entire chapter to establish new procedures to acquire weight volume factors.

    81 - 81.2 - Removes captions and direction for trespass cruises and combines trespass cruises direction with new FSH 2409.12b, Timber and Forest Products Trespass/Theft Procedures. Establishes new captions and direction for “Weight to Volume Factors.”

WO AMENDMENT 2409.12-2008-1 2409.12_80 EFFECTIVE DATE: 07/23/2008 Page 2 of 18 DURATION: This amendment is effective until superseded or removed.

    FSH 2409.12 TIMBER CRUISING HANDBOOK

    CHAPTER 80 WEIGHT FACTOR DETERMINATION

Digest--Continued:

    82 Establishes new code and caption and sets forth direction for “The Development of Weight to Volume Factors.”

    83 Establishes new code and caption and sets forth direction for “Published Tables for Weight to Volume Factors.”

    84 Establishes new code and caption and sets forth direction for “Using Weight Factors When Processing the Timber Cruise.”

WO AMENDMENT 2409.12-2008-1 2409.12_80 EFFECTIVE DATE: 07/23/2008 Page 3 of 18 DURATION: This amendment is effective until superseded or removed.

    FSH 2409.12 TIMBER CRUISING HANDBOOK

    CHAPTER 80 WEIGHT FACTOR DETERMINATION

    Table of Contents

81 WEIGHT TO VOLUME FACTORS ......................................................................... 4

    81.1 Documenting Weight Factors .......................................................................................4 82 THE DEVELOPMENT OF WEIGHT TO VOLUME FACTORS ............................... 4

    82.1 Traditional Log Scaling ................................................................................................5

    82.11 Special Studies ........................................................................................................8 82.2 Xylodensimeter ............................................................................................................9 82.3 Chunk Scaling ..............................................................................................................9

    82.31 Large Chunk Procedure ......................................................................................... 14

    82.32 Small Chunk Procedure ......................................................................................... 15

    82.33 Equipment ............................................................................................................ 16

    82.34 Tree Selection Procedures ..................................................................................... 16 83 PUBLISHED TABLES FOR WEIGHT TO VOLUME FACTORS .......................... 16

    84 USING WEIGHT FACTORS WHEN PROCESSING THE TIMBER CRUISE ....... 17

WO AMENDMENT 2409.12-2008-1 2409.12_80 EFFECTIVE DATE: 07/23/2008 Page 4 of 18 DURATION: This amendment is effective until superseded or removed.

    FSH 2409.12 TIMBER CRUISING HANDBOOK

    CHAPTER 80 WEIGHT FACTOR DETERMINATION

81 WEIGHT TO VOLUME FACTORS

    Selling forest products by the ton, or 100 percent weight scaling, differs from traditional log scaling where individual logs are measured for size and a Log Rule is used to determine a board or cubic foot product volume. One hundred percent weight scaling can be used to sell forest products when reliable weight factors can be obtained and facilities with approved weight scales are available.

    One hundred percent weight scaling has the same standards for load accountability (FSH 2409.15, sec. 27) and weight scale certification (FSH 2409.15, sec. 25 and the B6.814 section of the FS-2400-6 and the G.8.1.4 of the FS-2400-13 Timber Sale Contracts) as traditional log scaling. One hundred percent weight scaling requires every load of material removed from a sale area be accounted for and weighed for payment. In addition, a weight to gross cubic volume factor is necessary to determine:

    1. The initial tonnage of material being offered based on timber cruise data.

    2. The initial pricing for material being offered.

    3. The volume of material removed for reporting purposes.

    81.1 Documenting Weight Factors

    The weight factor for a forest product may change by species, geographic location (latitude, aspect, elevation, site), live/dead, product, harvesting practices (how long the material remains in the woods after felling), tree age, season, climatic conditions, and probably many other factors. For 100 percent weight scaling, the intent is to use a factor that represents a reasonable average of the weight factors encountered during the life of a timber sale or group of timber sales. The regional or forest measurement specialist, based on experience, field data, and the value of material being sold, shall determined the proper weight factor for any situation.

    As a minimum, weight factors must be specific to a species or species groups. Each weight factor used when processing a timber cruise must be documented in the sale folder. As a minimum, the documentation must include the weight factor, the source of the weight factor, and the material to which the factor will be applied.

    82 THE DEVELOPMENT OF WEIGHT TO VOLUME FACTORS

    Regardless of the method used to determine a weight factor, if data is collected, the following standards must be met for each weight factor. There must be a minimum of 10 observations and the sampling error for the calculated factors must be 15 percent or less at the 95 percent confidence level. An observation is defined as either a load of logs or an individual tree.

WO AMENDMENT 2409.12-2008-1 2409.12_80 EFFECTIVE DATE: 07/23/2008 Page 5 of 18 DURATION: This amendment is effective until superseded or removed.

    FSH 2409.12 TIMBER CRUISING HANDBOOK

    CHAPTER 80 WEIGHT FACTOR DETERMINATION

    Acceptable procedures for the development, validation, and use of weight factors for the sale of forest products are illustrated in section 82.1. If a different procedure is used, that is a procedure not described in this handbook; the procedure must be documented and approved by the regional forester.

    82.1 Traditional Log Scaling

    This method uses information for completed traditional scaled sales (historical information). To use this method, the following information must be available by load:

    1. Species and product composition by load.

    2. Gross cubic volume by load (volume determined by truck scale is not acceptable for

    this procedure). Board foot volumes are not acceptable.

    3. Net load weight (this is the gross weight minus the tare weight, or the weight of the

    empty truck subtracted from the weight of the loaded truck).

    4. Sale location.

    As a minimum, a separate weight factor is calculated for each species or species group. To use historical scale information, all loads must be single species or species group. A load is considered single species if 95 percent of the load volume is from a single species.

    Consider each load as a separate observation. An average weight factor is calculated by dividing the sum of the net load weight for all loads by the sum of the gross cubic volume for all loads.

     n NetWti(i1 WtFacn GrsVoli( i1

Where:

     thNetWt = The net weight for the i load. ithGrsVol = The total gross volume for the i load. i

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    FSH 2409.12 TIMBER CRUISING HANDBOOK

    CHAPTER 80 WEIGHT FACTOR DETERMINATION

    The sampling error is calculated using the individual load information. The sampling error for the weight factor is computed using the formula described below:

     SEE100t~ WtFac?

    Where:

     E = Sampling error.

     n = Sample size.

     t = Students ‘t’ distribution.

    SD SEStandardError n

    SDStandardDeviation

    nnn222~NetWtWtFacGrsVol2WtFac;;NetWtGrsVoliiii(((~1i1i1i1~~2~;;n1~GrsVol?~?

    n~GrsVoli(~i1GrsVolMeanGrossVolume~n~~?

To calculate the sample size needed to achieve a specific sampling error, use the following

    equation:

     22tCV~ n2~E?Where:

    SD CVCoefficientofVariation100~ WtFac?

An example of calculating weight factors using the traditional log scaling method is provided in

    exhibit 01.

WO AMENDMENT 2409.12-2008-1 2409.12_80 EFFECTIVE DATE: 07/23/2008 Page 7 of 18 DURATION: This amendment is effective until superseded or removed.

    FSH 2409.12 TIMBER CRUISING HANDBOOK

    CHAPTER 80 WEIGHT FACTOR DETERMINATION

    82.1 - Exhibit 01

    Traditional Log Scaling

    NetWt*Grs22 Load GrsWt TareWt NetWt Spec Prod GrsVol NetWt GrsVolVol 11150 69780 26320 43460 A 1 1067.1 1888771600 1138702.4 46376166 11151 63800 25360 38440 A 1 990.8 1477633600 981684.6 38086352 11152 71020 26280 44740 A 1 1035.0 2001667600 1071225.0 46305900 11153 65840 25400 40440 A 1 766.2 1635393600 587062.4 30985128 11154 69600 26420 43180 A 1 946.6 1864512400 896051.6 40874188 11155 66100 26340 39760 A 1 956.0 1580857600 913936.0 38010560 11156 70180 25420 44760 A 1 1268.1 2003457600 1608077.6 56760156 11157 64480 26320 38160 A 1 962.5 1456185600 926406.3 36729000 11158 71550 26450 45100 A 1 1372.5 2034010000 1883756.3 61899750 11159 67410 25890 41520 A 1 945.1 1723910400 893214.0 39240552 Total 419560 10309.9 17666400000 10900116.2 435267752

Calculate weight factor for Species A using information in exhibit 01, Traditional Log Scaling:

    NetWt419560(WtFac40.6910309.9GrsVol(

    Determine the sampling error for the data shown in exhibit 01, Traditional Log Scaling:

    n~GrsVoli(~10309.9i1GrsVol1031.0~~n10?~~?

WO AMENDMENT 2409.12-2008-1 2409.12_80 EFFECTIVE DATE: 07/23/2008 Page 8 of 18 DURATION: This amendment is effective until superseded or removed.

    FSH 2409.12 TIMBER CRUISING HANDBOOK

    CHAPTER 80 WEIGHT FACTOR DETERMINATION

    nnn222~NetWtWtFacGrsVol2WtFacNetWtGrsVol;;iiii(((~1i1i1i1~SD~2~n1;;~GrsVol?~?

    2117666400000(40.69)(10900116.2)2(40.69)(435267752)~~2~;;91031.0??

    5.5196

    SD5.5196~~SE1.7455~~n10??

    SE1.7455E100t1002.269.69~~WtFac40.69??

    Using the SD and the mean gross volume given above, determine the number of samples needed to achieve a 5 percent sampling error with a 95 percent confidence (t = 2).

    SD5.5196CV10010013.565~~WtFac40.69??

    2222tCV213.565;;;;~~n3022~~E;;5??

    82.11 Special Studies

    Traditional log scaling may be used on active sales to determine weight factors in the same way historical information is used from completed scaled sales. A number of single species loads will be selected for traditional scaling and weighing from an active sale where load weight is available. The sale can either be a sample weight or a 100 percent scaled sale. The data can also be collected as a special study from a sale sold as tree measurement providing an adequate location for log rollout is identified, certified scalers, and cubic scaling rules are used to determine load volume, and certified weight scales are used to determine net load weight. (Note: The measured gross cubic volume for all logs on each selected load must be used to determine load volume. Loads may not be subsampled for volume determination when developing a volume to weight factor.)

WO AMENDMENT 2409.12-2008-1 2409.12_80 EFFECTIVE DATE: 07/23/2008 Page 9 of 18 DURATION: This amendment is effective until superseded or removed.

    FSH 2409.12 TIMBER CRUISING HANDBOOK

    CHAPTER 80 WEIGHT FACTOR DETERMINATION

To use this method consider the following for each load:

    1. Each load must be single species or species group.

    2. A load is considered single species if 95 percent of the load volume is from a single

    species.

    3. Each load will be considered a separate observation.

    An average weight factor is calculated by dividing the total net load weight for all loads by the total gross cubic volume for all loads. The sampling error is calculated using the individual load information (see example in sec. 82.1).

    82.2 Xylodensimeter

    The use of the Xylodensimeter is dependent on the user being able to distinguish the heartwood sapwood boundary in an increment core and being able to process the increment core without losing moisture from the core during handling. Because of these requirements, the Xylodensimeter is usually not practical for determining the weight of green material, but can be an acceptable tool for determining the weight factor for sound, older, dead material.

    When using the Xylodensimeter on standing trees, take a minimum of three cores on each tree at equally spaced locations on a line that circumscribes the tree at diameter at breast height (DBH). The individual weight factors derived from each core will be averaged to give a single weight factor for the tree.

    When using the Xylodensimeter on felled trees, take one core at DBH and at each 16 foot intervals from the stump to the merchantable top. The individual weight factors derived from each core will be averaged to give a single weight factor for the tree.

    Consider each tree a separate observation. A mean, or average, weight factor is calculated for the population by adding the average tree factors together and dividing by the number of factors. The sampling error is calculated using the average weight factors for each individual tree. 82.3 Chunk Scaling

    Chunk scaling is a destructive sampling process and refers to scaling and weighing pieces, or chunks, of a tree in a field setting. This procedure was developed to allow local units to develop or validate weight factors as necessary with minimal equipment, personnel, and dollar expenditures. Unlike the traditional load scaling procedures, “chunk scaling” does not require

    special scaling facilities, motorized equipment to manipulate logs, certified production scalers, or weight scales certified for commercial transactions.

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    FSH 2409.12 TIMBER CRUISING HANDBOOK

    CHAPTER 80 WEIGHT FACTOR DETERMINATION

    Chunk scaling requires a set of field procedures be followed to select the chunks, and all measurements be taken by someone with at least a Utilization Scaling Certification. There are two accepted sets of field procedures for selecting the chunks within each tree; the large chunk procedure (described in sec. 82.31) and the small chunk procedure (described in sec. 82.32). The end diameters of each chunk are determined by the procedure specified in the Cubic Scaling thHandbook (FSH 2409.11a, sec. 21.3) with diameters being recorded to the nearest 10 of an inch thor the nearest 100 of a foot depending on the measuring device being used. Chunk length must not exceed 8 feet in length for weight studies (the taper, or change in taper rates for pieces longer than 8 feet can distort the cubic volume for the chunk resulting in a distorted weight factor for ththe piece). The length of a chunk is recorded to the nearest 100 of a foot. If the chunk was not

    cut square, measurements are taken on both the short and long sides and averaged. Cubic thvolume for the chunk is calculated using the Smalian formula and recorded to the nearest 100

    of a cubic foot. The chunk weight is recorded to the precision of the weight scale being used.

    The weight of all chunks and volume of all chunks are summed for each tree, and each tree is considered to be a single observation, not each chunk. An average weight factor for the population is calculated by dividing the total weight for all trees by the total gross cubic volume for all trees.

     n TreeWti( i1WtFacn TreeVoli( i1

    Where:

     th TrWt = Sum of the chunk weights for the i tree. ith TrVol = Sum of the chunk volumes for the i tree. i

    The sampling error is calculated using the sum of the weights and volumes for individual trees using the following formula:

     SEE100t~ WtFac?

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