PROPERTIES OF

PLANTATION GROWN KOA (ACACIA KOA A. GRAY )

Brian H. Bond1, Ian Wilton2 and Nick S. Dudley3

1Department of Sustainable Biomaterials, Virginia Tech, 2Exchange Student,

and 3Hawaiian Agricultural Research Center 3 Hawaii Agriculture Research Center

Introduction

• In Hawaii, Koa (Acacia koa) is a valuable tree species economically, ecologically, and culturally

• Endemic to Hawaii

• Used in furniture, cabinetry, musical instruments, and a wide variety of other decorative and craft products

Value of Lumber

1.7 Board Feet

Or $162/bd ft.

.77 Board Feet

Or $84/bd ft.

• High valued lumber specie• Average prices of 5.00 - $15.00

U.S. per bdft

• Premium instrument grade with

vertical grain and heavy figured

material can sell for over $100

U.S. per bdft

• Important features

• Color (heartwood)

• Figure

Examples of Variability and Grade

Problem Statement

• Limited supply

• Sources of koa are diminishing

• No harvesting of koa is currently permitted on state owned land in

Hawaii

• Potential Solution

• Koa has been identified as adaptable to plantation management

• Plantation koa could theoretically become a substitute source

• Presently little is known about the properties of plantation-

grown koa

• Planted koa will serve as a substitute resource only if properties

that add value are present.

Objectives

• Determine the heartwood/sapwood ratios, specific gravity,

hardness and for Hawaiian plantation-grown koa and

compare them to published data from natural grown

material

Methods

• Nine plantation-grown koa trees in Hawaii were harvested by HARC in 2007

• 7 trees five years of age

• 2 trees nine years of age

• Samples were prepared and mailed to Blacksburg, VA

• All were then allowed to reach an equilibrium at 12% EMC

Methods: Heartwood/Sapwood

• Discs were sanded and photographed

• Color and florescence

• Digital image analysis (ImageJ64) was then used to measure the percent of heartwood and sapwood within each cross section• Visual and software assisted

Difficulties Measuring Heart/Sapwood

• Confusion with stain caused

by the vascular wilt fungus

Fusarium oxysporum

Methods: Specific Gravity/Density,

Hardness• Sections for each tree were then prepared and then

tested for specific gravity (ASTM 2395) and hardness

(ASTM D143)

• Four samples for each piece were taken

• Two sapwood

• Two heartwood

• Subsamples were cut and scanned using a QTRS-01X

Tree Ring Analyzer to measure density variation from the

bark to the pith and within the entire cross section

• Data was then compared to published values, when

available

Results 5-Year-Old Plantation Koa

• 73% Sapwood

• 27% Heartwood

9-Year-Old Plantation Koa

• 23% Sapwood

• 77% Heartwood

Results

0

10

20

30

40

50

60

70

80

90

100

#10 R16 C15 #10 R7 C2 #15 R17 C6 #3 R15 C1 #5 R10 C3 #5 R12 C7 #5 R15 C8 1997 # 1 1997 #2

Pe

rce

nt

Sample

Percent Sapwood and Heartwood

% Sapwood

% Heartwood

Results

•Specific Gravity at 12% MC• 0.52 Sample Average • 0.55 for heartwood1

• 0.49 for sapwood1

1No statistical difference

• Values from literature:

• 0.55 (Skolmen, 1974; Alden 1995; and FPL, 2010)

• 0.46 (Gerry 1955)

Results

0.00

0.10

0.20

0.30

0.40

0.50

0.60

#10 R16C15

#10 R7 C2 #15 R17 C6 #3 R15 C1 #5 R10 C3 #5 R12 C7 #5 R15 C8 1997 # 1 1997 #2

Sp

ec

ific

Gra

vit

y

Sample

Specific Gravity - (12%MC)

Sapwood

Heartwood

Results

•Density • Ranged from 321-803kg/m3

• 515 average

• 96 stdv.

•Published values of density

• 480 – 1281 kg/m3

• Measurement criteria not reported (%MC)

Density Variation• Large variability from bark to pith

• Within and between samples• 5-year old

Density Variation• 9-year-old

Results: Hardness

• Hardness• Average hardness was 786

• Large variation (standard deviation 303 lb)

• Min. 402

• Max. 1921

• No statistical difference between sapwood and heartwood

• Varied between samples

• Reported values at 12% MC • 8281-1,0112 lbs

1Gerry, 1955 2FPL, 2010

Results Hardness

0

200

400

600

800

1000

1200

1400

1600

1800

#10 R16 C15 #10 R7 C2 #15 R17 C6 #3 R15 C1 #5 R10 C3 #5 R12 C7 #5 R15 C8 1997 # 1 1997 #2

Inc

h P

ou

nd

s M

ea

su

red

at

12

% M

C

Sample

Hardness (in. lb.)

Results

• Large within sample

variability

• 1921

• 640

• 875

Summary

• Heartwood/Sapwood• 5 year old trees

• 73% Sapwood and 26 heartwood

• 9 year old trees

• 23% Sapwood and 77% heartwood

• Specific Gravity• 0.52 average

• Between reported values

• No relationship found between S.G. and heartwood/sapwood

• Hardness• Average was 786 lbs

• Lower than reported values

• Large variations found within and between samples

Future Work

• Determine if there is a relationship between color and

density

• The Hawaiian koa wood classification system appears to be

based on a relationship between color and density

• Determine shrinkage coefficients, MOE and MOR

• Compare to published values

Acknowledgements

•HARC: Maunawili Experiment Station• Ian Wilton

• N.S. Dudley

• Tyler Jones