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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