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Why Use Count Plots?

A Comparison of Various Count to Measure Ratios

In the BC Interior

Presented by:Jim Wilson RFT, ATE

May 2008

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Overview Why are we sampling?

What are we sampling?

Why sample with count plots?

Variations of count plots

Study

Results

Recommendations

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Why are we sampling?

Cost prohibitive to measure every tree

For appraisal purposes, we require cruise estimates to calculate the stumpage rate

Decision is based on: What sampling error can we live with based

on our budget?

unfortunately, the min 2SE is set for us

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What are we sampling? For appraisals – net volume ±15% 2SE

Sampling for net volume has two equal parts:

BA/ha (tree count) VBAR (measure trees)

We could just as easily sample for any other attribute: $ value, stems/ha, etc.

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What are we sampling?

Questions:

Are the items to sample:

More or less variable?

More or less costly to collect?

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Why sample with count plots? More variability, more samples needed

Tree count is usually more variable than the measure trees

Counting trees is easy and cheap, measuring trees is costly

Measuring trees is 50% of the answer, getting tree count is the other 50% You decide how much of each to sample

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Variations of Count Plots

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Variations of Count Plots

Which sample better covers the ground and covers the variability of the stand?

Selecting trees with a Big BAF better distributes measure trees – more efficient

Count:Measure plots clump measure trees into clusters – less efficient

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Study Selected 7 interior cutting permits Northern and Southern Interior Stand types: SB, FPyL, Pl(S) All full measures:

Randomly selected plots to start Ratios 0:1, 1:1, 2:1, 3:1, 5:1 (count:measure) Graphed net vol/ha, ISR $/m3, cruising costs

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Results : Net Vol/ha SB stand

0

100

200

300

400

500

Ratio 0:1 Ratio 1:1 Ratio 2:1 Ratio 3:1 Ratio 5:1

$0

$2,000

$4,000

$6,000

$8,000

Net Vol/ha

Crew Costs

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Results: Stumpage Rate SB stand

0

10

20

30

40

50

Ratio 0:1 Ratio 1:1 Ratio 2:1 Ratio 3:1 Ratio 5:1

$0

$2,000

$4,000

$6,000

$8,000

ISR $/m3

Crew Costs

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Results : Net Vol/ha PlS stand

0

50

100

150

200

250

300

350

Ratio 0:1 Ratio 1:1 Ratio 2:1 Ratio 3:1 Ratio 5:1

$0

$2,000

$4,000

$6,000

$8,000

Net Vol/ha

Crew Costs

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Results: Stumpage Rate PlS stand

0

5

10

15

20

25

Ratio 0:1 Ratio 1:1 Ratio 2:1 Ratio 3:1 Ratio 5:1

$0

$2,000

$4,000

$6,000

$8,000

$/m3

Crew Costs

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Results

Tree Count CV:

SB stand:0:1 – 5:1 86 plots - 39%

PlS stand:0:1 – 5:1 117 plots - 38%

Each of the runs by stand had the same number of plots and therefore the same CV

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Results

VBAR CV: SB stand:

0:1 – 397 trees - 28% 1:1 – 195 trees - 28% 2:1 – 136 trees - 28% 3:1 – 107 trees - 29% 5:1 – 74 trees - 30%

PlS stand: 0:1 – 653 trees - 23% 1:1 – 337 trees - 24% 2:1 – 212 trees - 22% 3:1 – 161 trees - 24% 5:1 – 117 trees - 23%

Why are we measuring so many trees?

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ResultsTrends:

Net vol/ha does not change using count plots averaged within ± 2%

Stumpage rate does not change using count plots averaged within ± 5%

CV is stable for VBAR (we are measuring too many!)

Cruising costs are 30% less using 1:1 ratio and 50% less using 5:1 ratio versus full measure plots

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ResultsOptimal solution to reach 15% 2SE

(using Kim Iles’ star_bar.xls):

SB stand: Using TC CV of 39% and VBAR CV of 28% 41 count plots & 41 VBAR trees Equivalent to 3.5 counts to 1 measure plot

PlS stand: Using TC CV of 38% and VBAR CV of 23% 37 count plots & 31 VBAR trees Equivalent to 7.2 counts to 1 measure plot

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Recommendations Use count plots in highly variable stands to

meet sampling error (more counts)

Use count plots in homogenous stands to decrease effort (less measure trees)

Use count plots in partial reduction areas

Use Big BAF to select measure trees and increase efficiency

Use count plots and spread out the trees!

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AcknowledgementsSrdjan Kragulj, RPF Timberline - Vancouver he helped provide all the stumpage calculations for each of the runs Kim Iles, PhD for spoon feeding me time and time again his STAR_BAR.xls program should be used by everyone to plan

cruises

John Bell, PhD for his short course and newsletter

(http://www.proaxis.com/~johnbell/)

Walter Bitterlich, PhD for making cruising so much easier

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Questions?

Jim Wilson, RFT, ATE

Cruise Compilation Manager

Timberline Natural Resource Group

Phone: 604-714-2897

Cell: 778-858-9123