Open Journal of Forestry
2014. Vol.4, No.1, 8-13
Published Online January 2014 in SciRes (http://www.scirp .o rg /journal/ojf) http://dx.doi.org/10.4236/ojf.2014.41002
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8
Mechanical Properties of Small Clear Wood Specimens of
Pinus patula Planted in Malawi
Felix Dalitso Kamala1, Hiroki Sakagami2, Junji Matsumura2*
1Graduate School of Bioresource and Bioenvironmental Sciences, Kyushu University, Fukuoka, Japan
2Faculty of Agriculture, Kyushu University, Fukuoka, Japan
Email: *matumura@agr.kyushu-u.ac.jp
Received September 21st, 2013; revised October 29th, 2013; accepted November 20th, 2013
Copyright © 2014 Felix Dalitso Kamala et al. This is an open access article distributed under the Creative
Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium,
provided the original work is properly cited. In accordance of the Creative Commons Attribution License all
Copyrights © 2014 are res erved f o r SC IRP and the owner of th e in tell ect u al p rop erty Felix Dalitso Ka mala et al.
All Copyri ght © 2014 are guarded by law and by SCIRP as a guardian.
Pinus patula is one of the major exotic species grown in Malawi mainly for saw-timber production. It is
native to Mexico. Little has been reported about the mechanical properties of the wood. The objective of
this study was to investigate the mechanical properties of Pinus patula in more detail, in order to provide
a basis for utilizing this resource. The mechanical properties of small clear wood specimens of Pinus pa-
tula were evaluated using 40 cm logs from 1, 3, 5, 7 and 9 m above the ground. Small clear wood speci-
mens were selected and subjected to a bending test in accordance with Japan Industrial Standards (JIS)
air-dry conditions. The growth rate did not affect the mechanical properties measured. There were signifi-
cant correlations at 1% level between air-dry density and Modulus Of Elasticity (MOE) (R = 0.85) and
between air-dry density and Modulus Of Rupture (MOR) (R = 0.83). There was also a significant correla-
tion between MOE and MOR at 1% level (R = 0.90). At about 12% moisture content, the tested five Pi-
nus patula families have average MOR and MOE of 105.17 MPa and 10.93 GPa, respectively.
Keywords: Pinus patula; Modulus of Elasticity; Modulus of Rupture; Malawi; Air-Dry Density; Wood
Introduction
In Malawi, high demand for wood coupled with high defore-
station rates has led to the increase in the adoption of exotic trees
and introduction of plantation forestry. Although wood is natu-
rally variable, fast grown trees produce wood, which may be
significantly different in properties, compared with wood from
slow grown trees. Furthermore, for trees grown as exotic, the
wood produced may have different properties from wood of the
same species in the original environment.
Pinus patula is one of the major exotic species grown in
Malawi. It is planted about 80% of Malawi’s 74,000 ha of
softwood plantation. It is native to Mexico. Tree height of Pinus
patula ranges from 30 m to 35 m and the diameter at breast
height ranges from 50 cm to 90 cm (Stanger, 2003). Under
favorable conditions, it may attain a hei ght of 15 m after 8 yea rs
and 35 m after 30 years. The species are mainly used for saw-
timber. Despite their wide use for structural purposes among
other uses, no detailed mechanical properties research has been
done to determine the strength of the species under Malawi
growth conditions. This is because, in Malawi, just like many
other species, research on Pinus patula has concentrated on the
height growth, volume and form. Against this background, a
study on the wood properties of Pinus patula wa s carried out
using the seed orchard established by the Forest Research In-
stitute of Malawi (FRIM).
The broad objective of the study was to find out and analyze
genetic factors on wood properties of Pinus patula in Malawi, to
recommend the possibility of the improvement of wood quality
and to contribute to sustainable management for plantation
forests. Specifically, the general study looked at the extent of
family and within family wood property variation of Pinus
patula in order to find out if selection for wood property inclu-
sion in tree breeding is possible. Kamala et al. (2013) looked at
the growth characteristics and wood density because of their
large influence on many other wood properties. A total of 15
trees from five families were studied. The growth rate for the
five families was significantly different. The present study looks
at the mechanical properties namely: Modulus of Rupture
(MOR), Modulus of Elasticity (MOE) and wood density. Mod-
ulus of rupture and modulus of elasticity are important properties
for the use of wood as a structural material. MOR is an indication
of the bending strength of a board or structural member, and
MOE is an indication of the stiffness. When analyzed among
trees and within a tree, mechanical property variation tends to
follow similar patterns to those observed in wood density. The
determination of MOR and MOE together with density is im-
portant to better understand their relationships. The relationships
among these properties are species specific, stronger in others
but weaker in other species. These relationships allow prediction
of effect of selecting one property to breed on the other proper-
ties. The relationships are also important in machine stress
grading.
*Corresponding author.
F. D. KAMALA ET AL.
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9
The main objective of this research was to look at the me-
chanical properties of Pinus patula in more detail, in order to
provide a basis for utilizing this resource in Malawi. In general,
this research seeks to provide reliable data for comparing the
mechanical properties of Pinus patula grown in Malawi with
various species. It also provides data, which may be used to
analyze the influence on the mechanical properties of such
factors as: distance of timber from the pith of the tree, height of
timber in the tree, etc. The study further seeks to provide data,
which can be used to classify the strength of Pinus patula grown
in Malawi for grading purposes.
Materials and Methods
Sampling
The samples used in this research were collected from Dedza
in Central Malawi (altitude 1737 meters above sea level). The
orchard used in this study was planted with forty-two families
without routine silvicultural treatments. Families were rando-
mized within each block. The total number of treatments (fami-
lies) was 42 in 4 replications. Plot size was 7 × 7 trees at a
spacing of 9 × 9 feet (2.74 × 2.74 m). The plantation was 30
years old, but for unknown reasons, some of the trees studied
were less than 30 years old.
This study looked at five of the 42 families. One tree per
family was used representing a total of five trees with repre-
sentative grow th rates . Table 1 shows the growth information o f
the five trees in terms of height, Diameter at Breast Height (DBH)
and height at 15 cm diameter. The 15 cm diameter is the mini-
mum merchantable diameter in Malawi. The mechanical prop-
erties of Pinus patula were evaluated using 40 cm logs from 1, 3,
5, 7 and 9 m above the ground. The logs were further cut into 20
mm × 20 mm × 32 cm specimens. The total number of small
clear wood specimens was 86. A lot of care was taken to avoid
any defect on the specimens. The specimens were selected and
subjected to a bending test in accordance with Japanese Indus-
trial Standards (JIS) air-dry conditions. The moisture content for
the specimens was about 12%.
Data Analysis
In order to find out the relationship between the mechanical
properties, scatter plots with regression line were produced
using Minitab statistical software. The relationship was com-
pared at individual tree and family levels. Analysis of variance
was run at family and height above the ground levels for Mod-
ulus Of Elasticity (MOE), Modulus Of Rupture (MOR) and
air-dry density. This was done in order to find out the extent of
variation of the properties among the families.
Table 1.
Volume growth information of f ive trees (five fa milies) of Pinus patula
at 30 years old.
Family DBH (cm) Height (m) Height at 15 cm
diameter (m)
1 30.0 26.0 18.9
2 34.0 27.7 20.2
3 28.0 23.2 16.7
4 31.0 23.5 19.3
5 27.0 23 15.1
Mechanical Properties of Juvenile Wood versus
Mature Wood
Data from a previous research (K amala et al., unpubl. dat a) on
tracheid length for the same sample trees was used to determine
juvenile and mature wood boundary. The study of the tracheid
length of the five families showed that there was a rapid increase
of tracheid length up to ring number 10 and then a stable pattern
towards the bark. Therefore, ring number 10 was assumed to be
the boundary between the juvenile wood and mature wood for
Pinus patula grown in Malawi. The data for the juvenile wood
and mature wood mechanical properties was subjected to an
analysis of variance to find out if the variation of the mechanical
properties was significant or not.
Grade Yield
Grading standard of physical and mechanical properties of
timbers from Southeast Asia and Pacific regions by For estry and
Forest Products Research Institute (FFPRI) in Japan and the
South African national standards were used to check the grade
yield using MOE and MOR sep ar atel y. Tables 2 and 3 show the
grading standard of mechanical properties of timbers from
Southeast Asia and Pacific regions by Forestry and Forest
Products Research Institute and the grades according to the
characteristic stress for South African Pine respectively.
Results and Discu ssion
Mechanical Properties
Table 4 shows the average mechanical properties for the five
trees from five families. The average air-dry density was uni-
form among the families with family five registering a slight
increase at 0.54 g·cm3. MOE was also comparatively uniform
with family five producing the highest MOE and MOR of 11.90
GPa and 111.47 MPa respectively.
Table 2.
Grading standard of mechanical properties of timbers from Southeast
Asia and Pacific regions by Forestry and Forest Products Research
Institute (FFPRI) (1975).
Grade MOE (GPa) MOR (MPa)
I - 7.35 - 58.8
II 7.45 - 10.3 58.9 - 82.4
III 10.4 - 13.2 82.5 - 107
IV 13.3 - 16.2 107 - 130.4
V 16.3 - 131 -
Table 3.
Mechanical grades accordin g to the characteristic stress for South Afri-
can Pine (SANS 10163, 2003).
Grade MOE (GPa)
xxx 7.79
Five 9.59
Seven 11.99
Ten 18
F. D. KAMALA ET AL.
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Table 4.
Average mechanical properties for the five families (Total five trees).
Family Air dry density
(gcm3) MOE
(GPa) MOR
(MPa)
1 0.50 (0.11)* 11 (3.42)* 101.34 (35.83)*
2 0.50 (0.07)* 11.54 (3.28)* 107.92 ( 28.25)*
3 0.50 (0.12)* 10.84 (3.23)* 110.77 ( 34.15)*
4 0.51 (0.11)* 10.47 (3.51)* 105.97 ( 32.95)*
5 0.54 (0.09)* 11.90 (3.59)* 111.47 ( 39.91)*
Note: *S tand ar d de vi a tio n.
Table 5 shows the summarized mechanical properties
among the five trees from fives families. The maximum MOE
and MOR were 16.72 GPa and 185.19 MPa respectively. The
maximum air-dry density was 0.69 gcm3. At about 12%
moisture content, the tested five Pinus patula families have
average MOR and MOE of 105.17 MPa and 10.93 GPa, re-
spectively.
Tables 6 and 7 show the analysis of variance (Anova) results
for MOE and MOR respectively. The Anova results show that
stem height had no significant effect on the mechanical proper-
ties. The results also show that despite the differences in growth
rate among the five trees from the five fami lies, the mec hanical
properties were not significantly different among them. This
shows that growth rate had no effect on the mechanical proper-
ties of the species.
This result is comparable to the results by Anon (1947) for
South African Pinus patula. He also reported no correlation
between timber strength and rate of growth. Craib (1939) also
concluded that the rate of growth did not affect lumber strength
in Pinus patula. The absence of influence of growth rate on
mechanical properties is an advantage to forest managers who
prefer higher growth rate to increase the volume yield of plan-
tations because the higher growth rate will not affect the
strength of the lumber produced. However caution should be
taken because although the density of softwoods is generally
not related to growth rate, density is directly related to the per-
centage of latewood in a growth ring (Shmulsky & Jones, 2011).
There is typically a large difference in density between early-
wood and latewood. For this reason, relatively wide latewood
zones indicate relatively high density. Because the strength of
wood increases with density, wide growth rings exhibiting a
low proportion of latewood may be of concern in products
where strength is important (Shmulsky & Jones, 2011). As long
as the increased growth rate does not decrease the proportion of
latewood within growth rings, there should be no problem in
applying silvicutural practices that increase the growth rate.
After applying these silvicultural practices, it will be also
important to find out the effect of increase of growth rate on the
wood properties. The lack of significant strength properties
variation among the five families is positive news for house and
building construction where there is a need to develop uniform
wood products from sustainable sources. P. patula has proved
to be an ideal timber for construction in South Africa. More
research on lumber strength and variation in Malawi should
allow further development of the species for these high value
products.
Table 8 shows mechanical properties of Pinus patula from
Table 5.
Summary of the mechanical properties (86 specimens).
Air dry density (gcm3)
MOE (GPa) MOR (MPa)
Minimum
0.33 4.14 51.78
Maximum
0.69 16.72 185.19
Std 0.09 3.19 31.46
Average 0.51 10.93 105.17
CV 17.87 29.88 29.53
Table 6.
MOE analysis of variance summary for family and stem height (86
specimens).
Source DF Type III SS Mean Squar e
Family 4 1827.11 456.77 NS
Stem hei ght 4 1171.92 292.97 NS
Error 78 93292.23 1196.05
Note: NS: Not Significant at 1 % level.
Table 7.
MOR analysis of variance summary for family and stem height (86
specimens).
Source DF Type III S S Mean Square
Family 4 19.10 4.88 NS
Stem
height
4 22.15 5.33 NS
Error 78 875.36 11.22
Note: NS: Not Significant at 1 % level.
Table 8.
Mechanical properties of Pinus patula from other countries (as cited by
Wright, 1994).
Location Mechanical property
Reference
Colombia MOE—10.8 GPa (Anon, 1980)
New Zealand MOE—7.65 GPa
MOR—70.6 MPa (Bier, 1983)
Mexico MOE—11.5 GPa
MOR—91.5 MPa (Ordonez et al., 1989)
South Africa MOE—10.8 GPa
MOR—71.6 MPa (Otto & Van Vuren, 1976)
Malawi MOE—10.93 Gpa
MOR—105.17 MPa This study
other countries at about 12% moisture content. In terms of
MOE, at 11.5 GPa, the Mexican Pinus patula had slightly
higher values than that of Malawi. The MOE values were al-
most the same as that of Colombia and South Africa at 10.8
GPa. Malawi Pinus patula bending strength and stiffness com-
pare favorably with the same species grown in other countries
listed in Table 8. Thus, its wood products (such as lumber,
composite panels, and structural composite lumber products)
can compete successfully with same products in the huge con-
struction markets of Southern Africa. This is especially true for
Oriented Strand Board (OSB), laminated veneer lumber (LVL),
and structural composite lumber (such as parallel strand lumber
F. D. KAMALA ET AL.
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(PSL), and laminated strand lumber (LSL).
Relationships among Wood Propertie s
Research has shown increased density to be strongly linked
to favorable strength, stiffness, hardness and working properties
of sawn timber, as well as wood pulp yield and paper-making
quality. The relationships among the mechanical properties in
this study were linear and positive.
Figures 1-3 show the relationships among air-dry density,
Figure 1.
Relationship between specific MOR and MOE among the five families.
Figure 2.
Relationship between specific MOR and density among the five fami-
lies.
Figure 3.
Relationship between specific MOE and density among the five families.
MOR and MOE. There were significant correlations at 1% level
between air-dry density and MOE (R = 0.85) and between air-
dry density and MOR (R = 0.83). There was also a significant
correlation between MOE and MOR at 1% level (R = 0.90).
These results are also comparable with results for East African
grown Pinus patula where wood density correlated significant-
ly with all green and dry lumber strengths (FFPRI, 1975).
The correlation of MOR and MOE with specific gravity is
typical ly very strong, as reported by Shottafer et al. (1972) and
Shepard & Shottafer (1992) for red pine, Wolcott (1985) for red
spruce, and Han (1995) for red maple. However, in some con-
iferous species, such as Abies fabri, Picea asperata, and Pinus
massoniana, the relationship of MOE to specific gravity is
weaker than the relationship between MOR a nd specific gravity
(Zhang, 1997), and this was also found to be true in fast-grow-
ing red pine (Deresse, 1998). It has been reported that wood
samples having similar specific gravity can a lso exhibit signifi-
cantly different strength values due to factors that may be asso-
ciated to other factors to which specific gravity is less sensitive
(Perem, 1958; Zhang, 1995; Deresse, 1998). Correlations in this
study indicate that controlling density would have a positive
effect on some mechanical properties.
Mechanical Properties and Grade Yield of Juvenile
Wood versus Mature Wood
Tables 9 and 10 show the analysis of variance results for
juvenile and mature woods among the five trees for MOE and
MOR respectively. Significant variation was noted between
juvenile wood and mature wood in terms of mechanical proper-
ties.
Figures 4-7 show the grade yield for both juvenile and ma-
ture wood according to MOE and MOR using grading standard
of mechanical properties of timbers from Southeast Asia and
Pacific regions (FFPRI, 1995). The grade yield for MOE in
juvenile wood was highest for Grade II followed by Grade I.
Grade III and Grade IV was lower. There was no grade yield
for Grade V according to MOE in juvenile wood (Figure 4).
The grade yield for MOR in juvenile wood was highest for
Grade III followed by Grade II and Grade I. Grade IV was
lower and the grade yield for Grade V was the lowest (Figure
5).
Table 9.
MOE Analysis of variance summary for juvenile and mature wood (86
specimens).
Source DF Type III S S Me an Square
MOE Juv/MAT 1 565.99 565.99**
Error 86 314.25 3.65
Note: **Significant at 1 % level.
Table 10.
MOR Analysis of variance su mmary for juvenile and mature wood (86
specimens).
Source DF Type III SS Mea n Square
MORJuv/MAT 1 40618.47 40618.47**
Error 86 44476.93 517.17
Note: **Significant at 1 % level.
F. D. KAMALA ET AL.
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Figure 4.
Specimen grade allocation in terms of MOE of juvenile wood according
to Grading standard of mechanical pro perties of timbers fro m Southeast
Asia and Pacific regions by FFPRI (1975). See Table 2.
Figure 5.
Specimen grade allocation in terms of MOR of Juvenile wood according
to Grading standard of mechanical pro perties of timbers fro m Southeast
Asia and Pacific regions by FFPRI (1975). See Table 2.
Figure 6.
Specimen grade allocation in terms of MOE of mature wood according
to Grading standard of mechanical pro perties of timbers fro m Southeast
Asia and Pacific regions by FFPRI (1975). See Table 2.
The grade yield for MOE in mature wood was highest for
Grade IV followed by Grade III. Grade V and Grade II was
lower. There was no grade yield for Grade I according to MOE
in mature wood (Figure 6).
The grade yield for MOR in mature wood was highest for
Grade V followed by Grade IV and Grade III. Grade II was
lower and there was no grade yield for Grade I according to
MOR in mature wood (Figure 7).
Figures 8 and 9 show grade yield for both juvenile and ma-
ture wood according to the South African national standards.
The grade yield for MOE in juvenile wood was highest for
Grade five at followed closely by Grade XXX. Grade Seven
was lower and the lowest grade yield according to MOE in
juvenile wood was in Grade Ten (Figure 8).
Figure 7.
Specimen grade allocation in terms of MOR of mature wood ac-
cording to Grading standard of mechanical properties of timbers from
Southeast Asia and Pacific regions by FFPRI (1975). See Table 2.
Figure 8.
Specimen grade allocation in terms of MOE of Juvenile wood
according to the South African standards (XXX is the rejects
category). See Table 3.
Figure 9.
Specimen grade allocation in terms of MOE of mature wood according
to the South African standards (XXX is the rejects category). See Table 3.
F. D. KAMALA ET AL.
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13
The grade yield for MOE in mature wood was highest for
Grade Ten at followed by Grade Seven. Grade II was lower and
there was no grade yield for Grade Five and XXX with both
grades yielding according to MOE in mature wood (Figure 9).
The grade yield according to MOE and MOR was different
for juvenile wood and mature wood. Some grades had high
yields in juvenile wood but low yields in mature wood. In other
cases, grades with high yield in juvenile wood were non-exis-
tent in mature wood. The results show that mature wood
yielded more grades with high values of MOE and MOR. This
clearly shows that mature wood for Pinus patula is superior in
strength and grade than juvenile wood. The implication for this
is that mature wood and juvenile wood should be used for dif-
ferent purposes to avoid underutilization. Uniform use of juve-
nile wood and mature wood for structural purposes would be
potentially dangerous because juvenile wood has inferior me-
chanical performance. To improve lumber strength, one can
process logs of older trees and minimize the use of the interior
portion of the log. Correct drying of the boards will increase the
most important lumber strength traits of modulus of rupture and
modulus of elasticity. Export of dried lumber of P. patula oc-
curs and should increase if uniformity can be maintained.
The common steps in establishing grades for lumber are:
testing of small clear specimens according to guidelines, estab-
lishing strength values and allowable properties, establishing
visual grading rules and lastly verifying grades using in-grade
testing. The contribution of this research towards creating an
accept able gr ading sy ste m is that it has clarified the variation of
mechanical propertie s. More mechanical propertie s data, through
testing of small clear wood specimens, from other areas in Ma-
lawi need to be accumulated.
This research has established first steps in assigning allowa-
ble mechanical properties for Pinus patula grown in Malawi.
After accumulating more small clear wood specimen data, test-
ing using the “in grade” approach, in which large representa-
tives samples of full size lumber can be tested to destruction is
recommended to compare the results. This will help in the as-
signment of standard grades that will ensure the efficient utili-
zation of Pinus patula structural lumber in Malawi.
Conclusion
At about 12% moisture content, the tested five Pinus patula
families have average MOR and MOE of 105.17 MPa and
10.93 GPa, respectively. There were significant correlations at
1% level between air-dry density and MOE (R = 0.85) and
between air-dry density and MOR (R = 0.83). There was also a
significant correlation between MOE and MOR at 1% level (R
= 0.90). There was no significant variation in MOE and MOR
among the five families. Stem level variation in MOE and
MOR is not significant. Mature wood of Pinus patula has more
superior mechanical performance than juvenile wood. The
growth rate did not affect the mechanical properties of the spe-
cies. This study suggests that it is potential to simultaneously
improve tree growth, density, and some mechanical properties
of the wood of this species. The results of this study are a
foundation that will provide a technical basis for the machine
grading of Pinus patula structural lumber in Malawi.
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