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Although many people think that 3-P can only be used for doing
more costly 100% timber inventories, it's really a method that can
be used to make a weighted random sample of a population at many
levels, including at the tree, acre, and timber stand. 3-P will
weight the higher volume units of any population for sample selection.
Since we may be concerned about getting more accurate cruise figures
for those polygons that have a higher value, we would prefer to
sample those polygons at a higher frequency than lower volume/value
polygons. Of course, any legitimate sample of a population must
be done using an unbiased selection process.
The primary advantage of 3-P selection is that it allows us to
make unbiased weighted sample selections; which permits us to achieve
a higher level of efficiency by leveraging the data collected from
fewer field samples.
We've tried and proven that the P-3-P method is much more economical
to use than traditional 100% 3-P and can even save time and money
when used in conjunction with conventional variable plot cruising.
Rather than taking measurements on every cruise plot, we make a
simple volume estimate at every plot, take full measurements on
those plots selected by the P-3-P program, and correct our estimates
with an adjustment ratio. The cruise statistics are then calculated
on the mean of the adjustment ratios.
In the event that a client has a 10,000-acre timbered tract with
no previously designated polygons, we could even employ our 3-P
program at the stand level to make a weighted selection of which
stands we will cruise.
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Conventional Strata Inventory
Procedure
A timberland owner requiring reconnaissance-level timber inventory
data for 100 polygons would normally be required to do a 10% cruise
of the area; or complete enough cruise plots in each of the 10 of
the polygons to achieve a standard error of 12% or less. The volumes
for the remaining 90 polygons would be the averages of volumes determined
for similar polygons of the 10 cruised. Rates of work production
assumptions include: 16 plots per man-day, average round trip distance
of 80 miles, and use of quad runners half the time.
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| Table 4. Conventional Strata
Inventory Procedure Cost to cruise 1-100 acre polygon. |
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Specific Requirement
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Units
|
Cost$/Unit
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Totals $
|
|
Field |
3
man-days |
500.00 |
1,500.00 |
|
Vehicle
Mileage |
240
miles |
0.60 |
144.00 |
|
Quad
use |
1.5
days |
35.00 |
52.00 |
|
Office |
0.5
man-day |
250.00 |
250.00 |
| |
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subtotal |
$ 1,946.00 |
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As table 4 shows, the approximate cost to cruise 1-100 acre polygon
would be $1,946.00. Therefore, the total cost to cruise all 10 100-acre
polygons, utilizing the conventional strata inventory procedure
would be approximately $19,460.00. Determining volumes for all 100
of the polygons, using this method, would take 2 cruisers approximately
4 weeks to complete.
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The goals for the hypothetical project:
· Stratify
the 10,000-acre timbered tract into no more than 100
individual polygons. Research shows that more accurate volumes
can be achieved for a tract by determining volumes for each individual
polygon, rather than just applying an average volumes for all
of the polygons within a similar timber type strata.
· Achieve an industry-acceptable 10% sampling error for
the
inventory effort.
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Table
3. 3-P procedure & associated
costs
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Specific Requirement
|
Units
|
Cost$/Unit
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Totals
$
|
|
Office- Purchase
current aerial photos and load onto a computer hard-drive
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100
|
12.00
|
1,200
|
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Office- stratify property into polygons on photos &
maps. Calculate polygon acreages.
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6 man-days
|
500.00
|
3,000
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Make volume estimates for
all polygons.
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Option 1-
Ocular estimate method
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8 man-days
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*5,170
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Option 2-
Photo extrapolation method
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6 man-days
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*3,000
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Use P-3-P to select polygons and complete cruises of
10 selected polygons:
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|
|
|
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Complete 150 plots in each polygon
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4 man-days
|
500.00
|
2,000
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Vehicle Mileage
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320 miles
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0.60
|
192
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Quad Use
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2 days
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35.00
|
70
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Office-cruise compilation and map prep
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0.5 man-days
|
500.00
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250
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| |
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Subtotal
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$ 2,512
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Polygon sample cruise cost * 10
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45 man-days
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25,512
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Office-Adjust the estimate volumes and prepare inventory
report
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2 man-days
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500.00
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$1,000
|
|
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48 man-days
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Subtotal
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$ 30,712
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Total Project Cost,
with use of the ocular estimate option
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56 man-days
|
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$35,882
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Total Project Cost,
with use of the photo extrapolation option
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54 man-days
|
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$33,712
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Summary. As shown by our example
calculations, the cost to cruise this area, using the conventional
inventory method, would be $43,120 and take 15 weeks to complete.
Using our P-3-P method, the project could be completed in 3 weeks
less time and cost $8,323 less than the conventional inventory method;
a 19% savings to the client. For a 50,000-acre inventory project,
our 3-P method could potentially save the client over $40,000. |
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