bark thickness should you care?

BARK THICKNESSBARK THICKNESSSHOULD YOU CARE?SHOULD YOU CARE?

Jim FlewellingJim FlewellingJim.flew@yahoo.comJim.flew@yahoo.com

GMUG, November 15, 2013GMUG, November 15, 2013

With a correction and addendum, Nov. 18, 2013.

OUTLINEOUTLINE

• 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!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 Coop1994 West-sideTaper Coop

• 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 Coop1994 West-sideTaper Coop

21

11

12 14

13 15

16

22 23

6

CANADA

MT ND

SD

ID OR

Suspicious volume cutoutsSuspicious 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 validationsSubsequent 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 validationsSubsequent volume validations

• 4% mean underestimate inside 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 -1993Bark Thickness Results -1993

From same client

Dble Bark /

DBH

Bark Thickness Results -2012Bark Thickness Results -2012

Bark Thickness Ratio (%)Bark Thickness Ratio (%)

• Mean error = 1.68 percentage points.• Mean error by stand range of 7 points.• No clear regional effects.

Bark Thickness Ratio - ANOVABark 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 - StructureBackground - 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?

SolutionsSolutions

• 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 / StandSolutions – 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- CAUSESSOLUTIONS- CAUSES

• Methods?• Climate / region / stand conditions ?• Seed source ?• Recent weather?• ??????

ADDENDUMADDENDUM

The remaining slides were attached after the presentation on November 15, 2013. These are copies of several pages taken from the 1994 Northwest taper cooperative report. These pages all refer to Douglas fir. English units (feet and inches) are used.

1994 Coop

Locations of plots in Washington with Douglas fir sample trees.

1994 Coop

Locations of plots in Oregon with Douglas fir sample trees.

1994 Taper Coop.

Douglas fir sample.

Bark Ratio = double bark thickness / DBH.

SIZE GROUPS

Trees are divided ibto twelve categories by DBH and total height. Horizontal lines represent cut lines. Not shown is a central trend line, used to subdivide each height group into to subsets representing a division between large and small DBHs.

TAPER COOP. DF residuals by Region, and DCLASS (DBH vs. Median for HT).

Area (ib), actual and predicted

Double bark thickness (DBT), and inside-bark area at BH