Density and Bending Strength Characteristics of North Western Nigerian Grown Eucalyptus Camaldulensis in Relation to Utilization as Timber
The density and bending strength of Eucalyptus camaldulensis Denhn (river red gum) grown in the North-western Nigeria were investigated. The tests were conducted using standard methods of testing clear wood specimens. ANOVA was used to analyze the data while Duncans New Multiple range Test (DNMRT) was used to separate the mean. The study revealed that, E. camaldulensis has an average density of 977.58 kg m-3. Similarly, E. camaldulensis had static bending strength of 133.33 N mm-2. E. camaldulensis collected from three geographical locations were significantly different for both the density and bending strength. The modulus of elasticity (stiffness) was 15219.89 N mm-2. Comparison between the density and bending strength of E. camaldulensis with other wood species commonly utilized as timber in Nigeria revealed that the wood was suitable for timber production.
to cite this article:
Babatola Olufemi and Abubarkar Malami, 2011. Density and Bending Strength Characteristics of North Western Nigerian Grown Eucalyptus Camaldulensis in Relation to Utilization as Timber. Research Journal of Forestry, 5: 107-114.
Received: March 01, 2011;
Accepted: April 27, 2011;
Published: June 15, 2011
The rate of wood consumption for construction and for furniture in northern
Nigeria is growing by the day. This part of the country relies heavily on wood
supplies from the south. Consequently, with population growth and the corresponding
upsurge in demand for wood and wood based products, there has been rapid growth
in the rate of wood consumption in the country. Wood supply is now dwindling
and its price becoming more and more expensive. The known species are getting
depleted. Above all, the rates of growth of the indigenous savanna tree species
are generally low and hence cannot meet the ever increasing demand of the people
for wood and wood products (Otegbeye, 2004). As such,
substantial areas of erstwhile very low productive forests have since been converted
into productive plantations of fast growing exotics such as Pinus spp.,
Eucalyptus spp., Tectona grandis, Gmelina arborea, Acacia spp.,
Azadirachta indica etc, by the various state forestry establishments across
the savanna zones (Momodu et al., 1997). Declining
availability of the prime economic species in timber market has led to the investigation
of lesser-used species (Oluwafemi and Adegbenga, 2007;
Kayode, 2007). Oluwafemi and Tunde
(2008) conducted a study on the quality of Sterculia setigera wood
species though for a different utilization end product (pulp and paper production).
This dictates the need to explore wood species other than the native ones with
a view to finding an alternative supply. The density is the most used criterion
for classification in the area of strength while the bending strength is relevant
in the domain of structural utilization (Lucas and Olufemi,
2001). It is against this backdrop that this research intends to explore
the utilization potentials of E. camaldulensis (Dehnh)-an indigenized
exotic species whose drought tolerance and adaptability have made it particularly
suitable for the semi-arid regions.
Eucalyptus species are native to Australia but grown extensively worldwide
as short rotation hardwoods for a variety of products and as ornamentals. They
have been successful as exotics because of their capacity for fast growth and
tolerance of harsh environments involving many effective adaptations: indeterminate
growth, coppicing, lignotubers, drought, fire, insect resistance and tolerance
of soil acidity and low fertility (Rockwood et al.,
2008). Eucalyptus species are the most valuable and widely planted
hardwood in the world (18 million ha in 90 countries (FAO,
2005). Eucalypts are grown extensively as exotic plantation species in tropical
and subtropical regions throughout Africa, South America, Asia and Australia
and, in more temperate regions of Europe, South America, North America and Australia.
In the regions of faster growth, rotations were as short as 5 years with yields
as high as 70 m3/ha/yr. Four species and their hybrids from this
subgenus, Eucalyptus grandis (EG), E. urophylla (EU), E. camaldulensis
and E. globulus, account for about 80% of the eucalypt plantations worldwide
(Rockwood et al., 2008).
Approximately four decades ago, the growing of Eucalyptus under community
forestry was to meet timber supply due to rise in demand; however, this orientation
has changed because of its emerging economic benefit to the land users (Meknonnen,
2000, Liu and Li, 2010). Kebebew
(2010) reported that growing of Eucalyptus increased the annual income of
rural farmers. In addition, Eucalypts are utilized worldwide for a wide array
of products including pulp for high quality paper, lumber, plywood, veneer,
solid and engineered flooring, fiberboard, wood cement composites, mine props,
poles, firewood, charcoal, essential oils, honey, tannin and landscape mulch
as well as for shade, windbreaks and phytoremediation (Tournier
et al., 2003; Gorrini, et al., 2004;
Krzysik et al., 2001; Foley
and Lassak, 2004; Coutts, 2005; Ogunwande
et al., 2005; Barton, 2007).
The success of this study is likely going to mitigate a number of problems
that are encountered in the movement of saw timber from the south to the north.
Among these are high cost of fuel, poor road network, labor cost, all in addition
to the problems of vehicle purchase and maintenance which raise the cost of
timber used for construction, furniture and other wood-based products in the
northern part of the country (Akpan, 2006). The price of
wood has always risen above the man can afford.
Based on the aforementioned, it is thought here that if alternative wood species
that are locally available are tapped, they could supplement or even substitute
the over depleted rain forest species available from the south. That could solve
some of the problems hitherto experienced. E. camaldulensis which has
been found to be highly adaptable to this region, is widely grown as wind break
to protect the any region from desert encroachment (_jackson
and Ojo, 1973; Sharma et al., 2005) has been
chosen for this study. The timber potential of E. camaldulensis is encouraged
from result of trials from other places (Sharma et al.,
2005). Therefore, the density and bending strength of E. camaldulensis
grown in the North-western Nigeria were investigated to confirm the possibility
of its use in the timber industry.
MATERIALS AND METHODS
Study area: The study was conducted in three locations in the former
Sokoto state, now Sokoto, Kebbi and Zamfara states. The three locations/study
sites are Gidan Kaura town (Gada Local Government area, Sokoto state) Kalgo
town, (Birnin Kebbi Local Government area, Kebbi state) and Kaura Namoda town
(Kaura Namoda Local Government area, Zamfara state). They are located in the
north western part of Nigeria between latitude 10° 8 and 13° 55
N and longitudes 3° 30 and 7° 15 E with a total land area
of approximately 94,588 km2 (Ojanuga, 2006).
Procedure for tree sampling: In each of the sites selected for the
study, matured E. camaldulensis trees were chosen by purposive selection
using a diameter of at least 20 cm to be considered as small diameter log as
a basis for selection in the three study areas for the research. Adekunle
(2007) only used tree with diameter at breast height of = 20 cm for timber
volume estimation. A total of 5 tree samples were selected from each of the
three research locations as in Mackes et al. (2005).
For density determination, specimens were cut to standard sizes in accordance
with STAS 6087:72 as cited by Pescarus and Cismaru (1979).
The bending strength test was carried out after almost four months of keeping
the samples in the open laboratory space and confirming the moisture content
at 12%. The test was done using the procedure prescribed by ASTM
Statistical analysis: The data collected for all test parameters were analyzed using analysis of variance (ANOVA) at p<0.05 probability level and Duncans New Multiple range Test (DNMRT) was used as a follow up analysis to separate the means.
Wood density: Values of density for all the 225 specimens were computed based on masses as shown in Table 1. At 12% moisture content, results showed that density variation ranged from 920.30 kg m-3 to 1084.25 kg m-3 with a mean value of 1003.58 kg m-3 in Sokoto. In Kebbi, the density variation was from 920.89 kg m-3 to 1082.07 kg m-3 with a mean value of 1008.77 kg m-3 while in Zamfara state, the density variation showed lower values ranging from 857.48 kg m-3 to 964.74 kg m-3, with a mean value of 920.39 kg m-3. The overall mean density value for E. camaldulensis across the three study sites was 977.58 kg m-3. Table 1 shows the density values of E. camaldulensis.
|| Density (kg m-3) of E. camaldulensis (Denhn)
from Sokoto, Kebbi and Zamfara states of north western Nigeria
|*1: Bottom, *2: Middle, *3: Top, Values in column with same
latter are not significantly different
|| Static bending strength parallel to grain (N mm-3)
|*1: Bottom, *2: Middle, *3: Top, Values in column with same
latter are not significantly different
|| Modulus of elasticity (MOE) in bending (N mm-2)
|*1: Bottom, *2: Middle, *3: Top, , Values in column with same
latter are not significantly different
Static bending: Static bending of E. camaldulensis was 133.33 N mm-2 (Table 2). In Sokoto, values for static bending ranged from 88.86 to 153.84 N mm-2 with a mean of 125.29 N mm-2. Static bending for Kebbi and Zamfara states ranged from 98.42 to 157.66 N mm-2 and 105.11 2 to 154.79 N mm-2 with mean values of 133.96 and 137.27 N mm-2, respectively. From the ANOVA, it is depicted that the locations show significant difference (p<0.05) while all other parameters were highly significant (p<0.01) in static bending stress.
Modulus of elasticity (MOE): In Sokoto, the modulus of elasticity in bending ranged from 9048.49 to 18428.92 N mm-2, with a mean of 14668.13 N mm-2 (Table 3). Values for Kebbi and Zamfara states ranged from 10568.52 to 18912.96 N mm-2 and 11203.37 to 19388.71 N mm-2, respectively. Mean values for the two states were 15276.99 and 16014.65 N mm-2 respectively. The overall mean value across the northwest ecological zone was 15319.89 N mm-2 (Table 3).
The density values of E. camaldulensis as revealed in this study favorably
compares with timber specification as stipulated in the standards of NCP
2 (1973). With the high density of E. camaldulensis the wood would
be especially attractive for general timber utilization in the north zone in
particular and in the country in general. By these values, the wood is at a
greater advantage over the light density species. Similarly, the wood stands
another advantage of repelling insects and fungi attack for which light wood
species are more susceptible (Raven et al., 1997).
The value tends towards the high density category in which case the use may
be restricted to structural construction. When compared with the available wood
species. E. camaldulensis will thus, be a very promising timber species.
Some of these local timber species and their densities include Triplochiton
scleroxylon (400 kg m-3), Pycanthus angolensis (480 kg
m-3), Khaya ivorensis (485 kg m-3), Gosweilerodendron
balsamiferum (497 kg m-3), Terminalia ivorensis (550 kg
m-3), Mitragyna ciliata (560 kg m-3) and Terminalia
superba (580 kg m-3) (Hall, 1998; Kwame,
2001). Others are Mansonia altissima (615 kg m-3), Entandrophragma
cylindricum (620 kg m-3) and Nauclea diderrichii (660
kg m-3) (Scheffer and Morrell, 1998; Ogunsanwo
and Onilude, 2002; Fuwape and Fabiyi, 2003). However,
the density of E. camaldulensis was lower than that of Gliricidia
sepium whic was 1025 kg m-3 (Oluwafemi and
Adegbenga, 2007). The fact that the density of E. camaldulensis was
higher than most commercial timber indicates that it is a heavy wood but not
as heavy as G. sepium. Poku et al. (2001)
stated that wood density is a good indicator for selection of wood for use.
It therefore implies that E. camaldulensis could be used where most of
the commercially available Nigerian timbers are being utilized like in building
and construction applications. The Analysis of Variance (ANOVA) shows that there
was highly significant difference between locations and trees as well as between
location/tree and tree region interaction. However, no significant difference
was observed between regions. The significant difference in the location may
be due to the site quality.
Results for static bending showed that E. camaldulensis with mean value
of 133.33 N mm-2 has a very high static bending stress. This places
the wood at an advantage as it compares favorably with some commercially important
wood species in Nigeria. For instance, Abura (Mitragyna ciliata) = 79
N mm-2, Afara (Terminalia superba) = 106 N mm-2,
Afromosia (Pericopsis elata) = 128 N mm-2, Ebony (Diospyros\crassiflora)
= 190 N mm-2, Ekki (Lophira alata) = 207 N mm-2,
Iroko (Chlorophora exelsa) = 130 N mm-2, Mahogany (Khaya
ivorensis) = 110 N mm-2, Obeche (Triplochiton scleroxylon,
from natural forest) = 77 N mm-2 and Teak (Tectona grandis)
= 107 N mm-2) and Nauclea diderrichii (209 N mm-2)
(Fuwape and Fabiyi, 2003). Static bending strength of
E. camaldulensis is higher than those of G. sepium = 120 N mm-2
and plantation grown T. scleroxylon = 62 N mm-2 (Ogunsanwo
and Onilude, 2002; Oluwafemi and Adegbenga, 2007).
However, it has similar bending strength with that of teak = 136 N mm-2
(from a slow growing provenance in India) reported by Bhat
and Priya (2004). The significant difference in the location may be due
to the site quality.
From the findings, it is clear that E. camaldulensis with a modulus of elasticity value of 15319.39 N mm-2 falls within the range of other eucalyptus species as well as with some timber species commonly used for structural purposes in Nigeria. Some of the eucalyptus species and their MOE values include E. paniculata (12100 N mm-2), E. pilularis (16800 N mm-2), E. diversicolor (17900 N mm-2), E. cloeziana (19521 N mm-2), E. microcorys (20500 N mm-2), E. grandis and E. terreticornis (20869 N mm-2) and E. paniculata (22700 N mm-2).
E. camaldulensis satisfies the requirements of NCP
2 (1973) in respect of the standards stipulation for timbers for structural
applications in the country. Values of modulus of elasticity of some of the
commonly used timbers in Nigeria include Ceiba pentandra (4280 N mm-2),
Triplochiton scleroxylon (5500 N mm-2), Antiaris africana
(5800 N mm-2), Alstonia boonei (6700 N mm-2),
Gossweiloredendron balsamiferum (7600 N mm-2), Daniellia klainei
(8100 N mm-2), Pycanthus angolensis (8445 N mm-2),
Khaya ivorensis (10000 N mm-2), Eribroma oblonga (10070
N mm-2), Chlorophora exelsa (11000 N mm-2) and
Mansonia altissima (11175 N mm-2) ALS (2000).
The modulus of elasticity of E. camaldulensis is higher than 6239 N mm-2
obtained for plantation grown T. scleroxylon (Ogunsanwo
and Onilude, 2002). Since most Nigerian timbers are fast declining in the
timber market due to over-exploitation to meet exportation demand, there is
the need to find good source of substitute for them (Ogunsanwo,
2000; Oluwafemi and Adegbenga, 2007). Therefore,
with the density and mechanical properties of E. camaldulensis obtained
in this study, its wood could be used various applications like building, construction,
flooring, cabinetry, furniture and other uses where high mechanical properties
are required. Results show that there is no correlation between modulus of elasticity
and density as increase in MOE does not translate to increase in density and
this is different to findings by Desch (1992). The ANOVA
revealed highly significant difference (p<0.05) among trees, locations regions
as well as all levels of interactions. The follow up analysis further confirms
this by showing significant differences between the means of Sokoto, Kebbi and
Zamfara states as well as the regions. The significant difference in the location
may be due to the site quality.
The large density values recorded places the wood at an elevated position of suitability in this respect enabling the wood to compete favorably with some commercially available timber species in Nigeria. The bending strength and modulus of elasticity values compare favorably and even superior to some of the species presently used in Nigeria. It can be concluded from the present study that E. camaldulensis is a promising species for timber industry in the north western part of Nigeria and in the nation in general.
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