United States

Department of

Agriculture

Forest Service

Pacific Northwest

Research Station

General Technical

Report

PNW-GTR-644

July 2005

Users Guide for Noble Fir

Bough Cruiser

Roger D. Fight, Keith A. Blatner, Roger C. Chapman, and

William E. Schlosser

Lowest merchantable whorl

Count merchantable noble fir

Topmost merchantable whorl
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Authors

Roger D. Fight is a research forester, U.S. Department of Agriculture, Forest

Service, Pacific Northwest Research Station, 10600 NE 51st Circle, Vancouver,

WA 98682; Keith A. Blatner is a professor and head, and Roger C. Chapman

is a professor, Department of Natural Resource Sciences, P.O. Box 646410,

Washington State University, Pullman, WA 99164; William E. Schlosser is Vice

President and CEO, Pacific Rim Taiga, Inc., P.O. Box 187, Pullman, WA 99163.
Abstract

Fight, Roger D.; Blatner, Keith A.; Chapman, Roger C.; Schlosser, William E.

2005. Users guide for noble fir bough cruiser. Gen. Tech. Rep. PNW-GTR644. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific

Northwest Research Station. 8 p.

The bough cruiser spreadsheet was developed to provide a method for cruising

noble fir (Abies procera Rehd.) stands to estimate the weight of boughs that might

be harvested. No boughs are cut as part of the cruise process. The approach is

based on a two-stage sample. The first stage consists of fixed-radius plots that are

used to estimate the number of merchantable noble fir trees per acre. The second

stage consists of sample trees that are used to estimate the weight of boughs per

tree. The software produces a report with the estimated weight of boughs per tree

and per acre.

Keywords: Noble fir, boughs, cruise, sampling, inventory, software.
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Users Guide for Noble Fir Bough Cruiser

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Introduction

The bough cruiser spreadsheet was developed to provide a method for cruising

noble fir (Abies procera Rehd.) stands to estimate the weight of boughs that might

be harvested. No boughs are cut as part of the cruise process. The approach is

based on a two-stage sample. The first stage consists of fixed-radius plots from one

or more transects across a stand. The first-stage plots are used to estimate the

number of merchantable noble fir trees per acre. The user chooses the size of this

plot and counts the number of merchantable noble fir trees. The second stage

consists of sample trees, randomly selected from those located on the first-stage

plots, and a count of competing trees from a 20.4-ft-radius plot surrounding each

sample tree. The second stage plots and sample trees are used to estimate the

weight of boughs per tree. Measurements taken on these trees relate to tree size,

age, and number and location of merchantable boughs. Other variables are the

number of competing trees on the 20.4-ft plot and geographic location.

The bough cruiser spreadsheet combines field measurements with a bough

weight model that was developed from a sample of 322 noble fir trees in the

Cascade Mountains of Washington and Oregon. The specific variables used to

predict bough weight are total tree height, merchantable bough height, diameter

at breast height (DBH) squared, age at breast height, whorl age for each merchantable whorl, the number of merchantable boughs on each whorl, and the total

number of trees within a 20.4-ft radius of the plot tree. In addition, an intercept

shifter was used that designates noble fir stands located north or south of the

Marion/Clackamas County line in Oregon. The overall model was significant at

the 0.0001 level with an adjusted R2 of 0.77 (Blatner and others 2005).

The spreadsheet template, this cruisers guide, and research papers describing

the study on which this model is based can all be downloaded from the Pacific

Northwest Research Station Web site http://www.fs.fed.us/pnw/data/boughs/

boughs_home.htm.

Once the spreadsheet is downloaded, it can be opened by double clicking the

file name in the file viewer. The spreadsheet was developed to work with

MicrosoftTM Excel® 5.01

 and newer versions. It has not been tested with other

spreadsheet software.

1

 The use of trade or firm names in this publication is for reader information and does not

imply endorsement by the U.S. Department of Agriculture of any product or service.
GENERAL TECHNICAL REPORT PNW-GTR-644

2

Overview of Bough Cruiser Spreadsheet

The Bough Cruiser spreadsheet consists of five sheets: instructions, data page,

calculator, report, and a tree data entry form. It comes preloaded with data and

results for a sample cruise. The instruction sheet has brief instructions for entering

data in the spreadsheet and viewing the results. The calculator sheet does intermediate calculations. No user input is required on that sheet. The report sheet (fig. 1)

shows the results of a bough cruise. All the information in this sheet is either

copied from the data page or calculated by the spreadsheet. The data page (fig. 2)

shows the data that are required from the cruise. The data in the tree data entry

form are included so that you have the data required to fully replicate the results

shown in the users guide. The data can be rearranged into sample plots with a

different number of sample trees per plot to test importing data for cruises with

different numbers of sample trees.

Figure 1—A sample report from the noble fir bough cruiser.
Users Guide for Noble Fir Bough Cruiser

3

Column headings for items in the data page sheet and the tree data entry form

are defined in the following tabulation:

Column Heading Definition

Calculated Green Weight The estimated green weight in pounds

(with no apparent moisture) of boughs for

the sample tree. This is calculated by the

spreadsheet.

Plot #.tree # Plots and trees are numbered in sequence

by the order they are entered into the

cruise program.

No. Merch. Noble Fir on Plot The number of dominant and codominant

noble fir trees with merchantable boughs

counted on the plot.

DBH Age Age at breast height based on counting the

whorls from the top of the tree down to

breast height.

DBH Diameter at breast height in inches.

Merchantable Height The height in feet of the topmost whorl that

is to be cut.

Total Tree Height Total tree height in feet.

Figure 2—A portion of the data page with sample data.
GENERAL TECHNICAL REPORT PNW-GTR-644

4

No. All Trees on 20.4’ Plot Total number of trees greater than 10 ft tall

on 20.4-ft-radius plot around the sample

tree, including the sample tree.

Whorl 1 Age Age of the topmost merchantable whorl based

on counting the whorls from the top of the

tree to the topmost merchantable whorl.

Whorl 1 Boughs The number of merchantable boughs to be

cut from the topmost merchantable whorl.

Whorl 2 to 15 Age Age of subsequent merchantable whorls.

Whorl 2 to 15 Boughs Number of merchantable boughs to be cut

from subsequent whorls.

Figure 3 illustrates the process for determining some of the values described in

the above tabulation. There are 17 whorls counting down from the top to breast

height making DBH age 17 years. Merchantable height is between whorl 9 and 10

making whorl 10 the first merchantable whorl and 10 years the age of merchantable whorl 1. The ages of merchantable whorls 2 through 8 are 11 to 17 years. The

process may extend below breast height if there are additional merchantable

boughs below breast height. A whorl within the merchantable range should be

skipped if it does not have at least two merchantable boughs on it.

Conducting the Bough Cruise

An Example

The following example of a bough cruise provides an overview of the process. A

10-ac unit of noble fir was cruised. First-stage plots were located 125 ft apart on

two transects across the long dimension of the unit and resulted in 12 stage-one

plots. A plot radius of 15 ft was used, and the desired number of stage-two sample

trees was two. There were four merchantable noble fir trees on the first plot. Two

of them were randomly selected for the stage-two sample. Measurements were

taken and recorded to provide values for each of the variables described in the

tabulation above. The process was continued on each of the remaining stage-one

plots. A portion of the data resulting from the cruise is shown in figure 2. The tree

measurements in this example are from trees that were measured to estimate the

bough weight model (Blatner and others 2005). The numbers of noble fir on stageone plots and the assignment of the measured trees to plots were made up to create

this example.
Users Guide for Noble Fir Bough Cruiser

5

Sample Design

The Noble Fir Bough Cruiser spreadsheet was designed to be used with two-stage

cluster sampling.2

 Stage one is used to get an unbiased estimate of the number of

merchantable noble fir trees in the unit. It uses a fixed-radius plot with the radius

chosen by the user. The radius should be set so that most plots will have at least

the number of trees desired for the stage-two sample and small enough to keep the

cost of counting the number of merchantable trees reasonable. Stage two is the

measurement of one or more merchantable noble fir trees located on each stageone plot. Merchantable trees are defined as having at least two not-previouslyharvested merchantable whorls up to the merchantable height. The cruiser calculations and input process assumes that the cruise design calls for all of the plots to

have the same number of sample trees. It is acceptable, however, to have a lesser

number or even zero sample trees on the occasional plot that is located where there

are not enough nobles on the plot to get the desired number of stage-two sample

trees.

2

 Chapman, R.C.; Blatner, K.A.; Schlosser, W.E.; Fight, R.D. [N.d.]. A sampling method

for inventorying noble fir stands to determine merchantable bough weight. Manuscript in

preparation. On file with: Roger C. Chapman, Department of Natural Resource Sciences,

P.O. Box 646410, Washington State University, Pullman, WA 99164.

Whorl 

number

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

Merchantable

whorl 

number

1

2

3

4

5

6

7

8

Merchantable

whorl

age

10

11

12

13

14

15

16

17

Merchantable

height

Breast

height

Figure 3—Diagram illustrating the numbering of whorls, merchantable whorls, and whorl

age for merchantable whorls.
GENERAL TECHNICAL REPORT PNW-GTR-644

6

The variables listed in the input form and their definitions in the above tabulation provide a description of the data that needs to be collected in the bough cruise.

The issues that need further elaboration are the methods for selecting the number

and location of plots and the sample trees. Chapman and others (n.d.) provide a

discussion of how to determine the number of plots and the number of sample trees

per plot (see footnote 2). The number of plots and sample trees per plot depend on

the desired accuracy, the available budget, the relative cost of measuring plots and

sample trees, and the relative variance between plots and within plots. A minimum

of two sample trees per plot are required to compute error terms for the sample.

Figure 4 adapted from Chapman and others suggests that two sample trees per plot

will often be a good choice. Between-plot and within-plot variance for completed

cruises can be viewed on the calculator sheet at cells J4 and J5. This may be

helpful in deciding how many sample trees to select per plot on future cruises.

Once the number of plots and the number of sample trees per plot have been

determined, field procedures need to be addressed. An easy way to locate the required number of plots is to use one or more transects through the stand being

cruised. The estimated total length of transect divided by the number of plots

provides the distance between plots along the transect. Follow the transect to the

first plot. Using the plot radius that you have chosen, count the number of merchantable noble fir trees on the plot. Randomly select the number of sample nobles

0

1

2

3

4

5

0 0.5 1 1.5

C2/C1

Number of trees to

measure in a plot

V2/V1=0.5

V2/V1=1.5

V2/V1=2.5

V2/V1=3.5

Figure 4—The most efficient number of stage-two sample trees per plot for a range of ratios of

between-plot and within-plot variance (V2/V1) and a range of ratios of measurement cost per

sample tree to the cost to establish and measure stage-one plots (C2/C1).
Users Guide for Noble Fir Bough Cruiser

7

called for in the cruise. Measure and record the following tree measurements for

each sample tree: DBH age, DBH, merchantable height, and the whorl data for

whorls to be cut. Also count the total number of trees taller than 10 ft on the 20.4-

ft-radius plot surrounding each sample tree. Go back to the transect and move

along the transect to the next plot and repeat the process until all plots and sample

trees have been measured and recorded.

Completing the Cruise Estimates

Once data collection is complete, the data need to be entered into the data page.

The data at the top of the data page are entered item by item. These data are used in

calculating the results and therefore must be entered before results can be viewed.

The tree data in the lower part can be entered item by item, but the tree data from a

bough cruise can also be imported in a block by use of the tree data entry form.

Data in spreadsheet format can be copied and pasted into the tree data entry form

and then imported into the data page by use of the import data macro located on the

toolbar. This will generally be the easiest way to enter the data from a bough cruise

into the bough cruiser spreadsheet. Choose the data import macro that corresponds

to the number of sample trees per plot in stage two of your sample. For illustrative

purposes in this users guide, we assumed that the sample was conducted on one or

more transects through a single stand and the number of sample trees desired per

plot was two.

The bough cruiser spreadsheet recalculates with each data entry, so once all

data have been entered in the data page, the results are ready to view in the report

sheet. The report sheet has an area where notes can be added. This is a good place

to document information that will be useful in writing the specifications for a

bough sale or instructions for harvesters. The report sheet is designed to be printed

to create a standard report for the estimated volume of boughs to be cut from a

unit.

This sampling scheme does not take into account some things that may affect

the actual yield of boughs. Broken terrain, steep slopes, pockets of low concentration of merchantable boughs, or long distances between parts of the unit and the

bough pickup point may result in parts of the unit being bypassed by harvesters

because the effort is too great. Because boughs are a relatively low-valued product,

it would not be cost effective to develop a sampling scheme that would account for
GENERAL TECHNICAL REPORT PNW-GTR-644

8

these factors. Making a separate estimate of the proportion that might be impractical to harvest and providing that information along with the cruise estimate is a

reasonable way of providing the full disclosure that bidders need to make bids that

accurately reflect the value of the boughs.

Metric Equivalents

When you know: Multiply by: To find:

Feet (ft) .3048 Meters

Acres (ac) .405 Hectares

Literature Cited

Blatner, K.A.; Fight, R.D.; Vance, N.; Savage, M.; Chapman, R.C. 2005. A

model to estimate noble fir bough weight. Western Journal of Applied Forestry. 20(1): 44-49.
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