BARK THICKNESS
SHOULD YOU CARE?
Jim Flewelling
Jim.flew@yahoo.com
GMUG, November 15, 2013
OUTLINE
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YES – You Should Care .
Background: 1994 NW Taper Coop
Suspicious volume cutouts.
Subsequent volume validations
Bark thickness results
Background: Structure of Taper Predictions.
Solutions.
Yes, You should care!
• For almost taper and volume equations
were derived from data where the key
variables included DBH (outside bark),
and inside bark volume or stem profile.
• If the equations are applied to areas where
bark thickness is different, results will be
bad.
1994 West-sideTaper Coop
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726 Douglas fir trees
Across the diameter range within stands.
7 predefined regions.
Eqns:
– Bark thickness at breast height
– Inside-bark profiles (conditioned at BH)
– Upper stem bark thickness equations
• Excellent residuals.
1994 West-sideTaper Coop
21
22
CANADA
23
12
14
ND
MT
11
13
16
SD
15
6
OR
ID
Suspicious volume cutouts
• Client was noticing a pattern of low volume
cutouts in one of the operating areas.
• Volume and taper equations are often the
innocent “usual suspects”
• This client put them on trial instead of just
complaining.
Subsequent volume validations
• 11 harvest age DF stands.
• 109 trees, selected across the DBH range.
• Standing measurements: DBH, HT, and
upper stem diameter (17’, 41’).
• Felled: Outside bark profile, and bark
thickness profile.
Subsequent volume validations
• 4% mean underestimate outside bark
volume.
• 0.0% mean error in outside bark volume
• Mean predicted bark ratio = .097
• Mean observed bark ratio = .116
• Do the Math!
• No other problems of this magnitude.
Bark Thickness Results -1993
From
same
client
Dble Bark /
DBH
Bark Thickness Results -2012
Bark Thickness Ratio (%)
• Mean error = 1.68 percentage points.
• Mean error by stand range of 7 points.
• No clear regional effects.
Bark Thickness Ratio - ANOVA
• Y = Bark Thickness Ratio at breast height
(%).
• Variance between stands =3.95
– Standard error = 1.99
• Variance between trees (within stands)=5.43
– Standard error = 2.33
Background - Structure
• Coop equations:
– BR eqn at breast height = f(DBH, HT, region).
– ib profile = f(DBH, HT, region)
– Profiles then conditioned on DBHib
• Less common:
– ib profile = f(DBH, HT)
• Software. Ability to supply DBHib?
Solutions
• Cruising can include bark thickness on a
small number of trees.
• For non-cruise applications, need survey
models.
• Try to find correlated variables.
Solutions – Few Trees / Stand
# of Stands
Trees/Stand
# of trees
size of 95% CI
on mean
20
10
200
1.92
20
20
400
1.93
20
40
800
1.89
40
10
400
1.30
40
20
800
1.30
40
40
1600
1.28
SOLUTIONS- CAUSES
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Methods?
Climate / region / stand conditions ?
Seed source ?
Recent weather?
??????