International Journal of Agriculture and Forestry

p-ISSN: 2165-882X    e-ISSN: 2165-8846

2018;  8(6): 220-226

doi:10.5923/j.ijaf.20180806.04

 

Wood Properties of Eucalypt Hybrid Clones Growing in Tanzania

Pima N. E.1, Iddi S.2, Chamshama S. A. O.3, Maguzu J.1

1Tanzania Forestry Research Institute, Morogoro, Tanzania

2Department of Forest Products and Technology, Sokoine University of Agriculture, Chuo Kikuu, Morogoro, Tanzania

3Department of Ecosystem and Conservation, Sokoine University of Agriculture, Chuo Kikuu, Morogoro, Tanzania

Correspondence to: Pima N. E., Tanzania Forestry Research Institute, Morogoro, Tanzania.

Email:

Copyright © 2018 The Author(s). Published by Scientific & Academic Publishing.

This work is licensed under the Creative Commons Attribution International License (CC BY).
http://creativecommons.org/licenses/by/4.0/

Abstract

Wood properties of nine year old Eucalypt hybrid clones grown at Lushoto, Kibaha, Kwamarukanga and Tabora in Tanzania were studied. Nine trees, three from each superior clone type representing small, medium and large trees were selected from each site. Samples were taken at breast height (1.3 m), 25% and 50% of tree height using standard procedures. Results of the study revealed overall mean basic density and fibre length values of 525.5–633.9 kgm-3 and 0.857–0.969 mm respectively. Modulus of elasticity and modulus of rupture ranged from 8525.2 to 12710.4 Nmm-2 and 72.6 to 108.5 Nmm-2 respectively. The cleavage in the radial and tangential directions ranged from 13.5 to 20.6 Nmm-2 and 14.9 to 22.0 Nmm-2 respectively. Compression ranged from 41.9 to 57.2 Nmm-2 and 7.8 to 13.7 Nmm-2 for shear strength. It is concluded that studied clones should be considered as a source of raw materials for pulp and paper production and for structural applications.

Keywords: Eucalypt hybrid clones, Basic density, Fibre length, Mechanical properties, Tanzania

Cite this paper: Pima N. E., Iddi S., Chamshama S. A. O., Maguzu J., Wood Properties of Eucalypt Hybrid Clones Growing in Tanzania, International Journal of Agriculture and Forestry, Vol. 8 No. 6, 2018, pp. 220-226. doi: 10.5923/j.ijaf.20180806.04.

Article Outline

1. Introduction
2. Material and Methods
3. Results and Discussion
4. Conclusions

1. Introduction

Eucalypt hybrid clones in Tanzania were introduced from Mondi South Africa in 2003 through Tanzania Forestry Research Institute (TAFORI) in order to test their adaptability in the Tanzanian environment before large scale planting. Experiments started in 2004 using Eucalyptus grandis x E. camaldulensis (GC), E. grandis x E. urophylla (GU), and E. grandis x E. tereticornis (GT) hybrid clones to test their adaptability in the Tanzanian environment before large scale planting. Ten (10) GC, one (1) GT and one (1) GU clones were planted at 15 trial plots established at different agro ecological zones of Tanzania. The clones are preferred for their fast growth with a short rotation, wide adaptability to site conditions, produce better quality wood and more uniform stands than most indigenous trees Eucalypt hybrid clones are mainly used in house construction, production of fuel wood, poles, telecommunication posts, fencing posts, electricity transmission poles, pulping and timber [1]. The suitability of raw wood for various uses is determined by its properties. Some of the important properties for the above end uses include basic density, fibre length and mechanical properties.
Wood basic density is one of the most often studied wood quality traits because it determines the economic value and is under high degree of genetic control [2]. It affects properties of various wood products such as pulp and paper, wood strength and wood quality [3]. On the other hand, mechanical properties of wood are an expression of its behaviour under applied forces. It refers to the ability of the material to resist external loads or forces tending to cause change in its size and alteration of its shape [4]. The uses to which wood is put require ability to resist loads and thus it is appropriate to examine the behaviour of wood when subjected to various forces. They are the most important characteristics of wood products for structural applications. Structural uses of wood and wood products include tie beams, purlins in house construction, floor joists and rafters in wood-frame housing, power line transmission poles, plywood roof sheathing and sub-flooring and glue laminated beams in commercial buildings.
Previous studies have found that hybrid Eucalypt clones generally have wood properties that are intermediate to their parental taxa [5-7] in Brazil, Kenya and Uganda respectively. Bal and Bektaş [8] studied the mechanical properties of E. camaldulensis, E. urophylla and E. grandis and found that the wood of the species had better mechanical properties which were within the specified range needed for plywood and furniture production. However, there are no available studies on physical and mechanical properties of wood of Eucalypt hybrid clones grown in Tanzania. The aim of this study was therefore to determine physical and mechanical properties of Eucalypt hybrid clones growing in Tanzania. The results from this study will be used as a basis of making recommendations which will lead to efficient utilization of clonal wood.

2. Material and Methods

Study Area
The study was conducted in four agro ecological zones namely Lushoto (Highland), Kibaha (Coastal), Kwamarukanga (Lowland) and Tabora (Inland Plateux) (Table 1). Lushoto site is located within Lushoto District, Tanga Region. Kibaha site is located in Ruvu North Forest Reserve, Pwani Region. Kwamarukanga site is located within Kwamarukanga Forest Reserve, Handeni District, Tanga Region. Tabora site is located within Tabora Municipality. Lushoto, Kibaha and Kwamarukanga sites have dry spell between June and September, short rains from October to December and long rains from March to May while Tabora receives long rains between November and April.
Table 1. Study area description
     
Experimental Design
The experiments were established by TAFORI in 2004 using Eucalypt hybrid clonal material from Mondi South Africa. Randomized complete block design with four replications and 12 treatments (Eucalypt hybrid clones) was used to set up these experiments at Lushoto, Kibaha and Kwamarukanga sites and 10 treatments at Tabora site (Table 2). Each clone type was represented once in each block. Each plot comprised 16 trees spaced at 2.5 x 2.5 m in a 4 x 4 arrangement. The experiments have 2 guard rows planted to avoid edge effect.
Table 2. Experimental design of Eucalypt hybrid clones
     
Sample selection
Lushoto, Kibaha, Kwamarukanga and Tabora sites were subjectively selected for data collection which represent other sites within the studied agro-ecological zones. Wood samples were obtained from three superior Eucalypt hybrid clones in terms of survival, Dbh, height, basal area, volume and biomass production i.e GC 581, GC 584 and GU 608 from Lushoto site; GC 15, GC 167 and GC 940 from Kibaha site; GC 514, GT 529 and GC 940 from Kwamarukanga site and GC 15, GC 584 and GC 940 from Tabora site. Purposive sampling was applied to select three sample trees (small, medium and large in Dbh) from each clone type and from each site. In total, 36 sample trees were felled and cut into logs for basic density, fibre length and mechanical properties determination.
Physical properties determination
Wood Basic Density
Stem sectional discs measuring 5 cm thick discs were taken from each log at different level at breast height (1.3 m), 25% and 50% of tree height. A wedge running from pith to bark was cut from each disk. Samples were cut at 25% and 50% of wedges’ total length. Wood basic density was determined in accordance with procedure described in BS. 373 [9]. The basic density of wood was calculated using water displacement for green volume determination.
Fibre length
Fibre length were measured in wood samples macerated with a 1:1 solution of glacial acetic acid and hydrogen peroxide solution for about 60°C for 48 hours for cell dissociation. Thirty straight and unbroken fibres from each sample were randomly selected for measurement using a projecting microscope to obtain a mean fibre length for each Eucalypt hybrid clone.
Mechanical properties determination
Sample preparation of test specimens
Each log was cross cut into three 1.5 m long billets at breast height (1.3 m), 25% and 50% of the tree height and each billet was sawn into 45 - 65 mm thick radial planks for easy air drying and labelled to indicate tree number and position in the tree. The cants were re-sawn radially into 30 mm x 60 mm x 1500 mm planks. Planks were air dried to about 12% moisture content and re-sawn into 20 x 30 x 1500 mm scantlings which were then planed to 20 mm x 20 mm x 1500 mm.
Determination of Modulus of Elasticity (MOE) and Modulus of Rupture (MOR) parallel to the grain
MOE and MOR were determined according to the standard procedures described by ISO 3349 [10] for MOE and ISO 3133 [11] for MOR. Specimens measuring 20 x 20 x 300 mm were taken and loaded using centre loading method to the Monsantor Tensiometer wood testing machine using a feeding speed of 0.635 mm/min and 500 kg deflection beam. Graph plotting was done manually following the mercury column along the scale in Newton. The load at which failure occurred was recorded on graph paper. MOR was calculated from the maximum load at which each specimen failed. MOE was calculated using load to deflection curve plotted on a graph by the machine. MOE and MOR were calculated using the following equations.
(1)
(2)
Where P = Maximum load in Newton (N)
L = Span (mm)
P1 = Load in Newton (N)
B = Width (mm)
D = Depth (mm)
Y = Deflection in mm at mid length at limit of proportionality
Determination of radial and tangential cleavage
Cleavage strength was determined according to the standard procedure described by Panshin and De Zeeuw [12]. Test specimens measuring 20 x 20 x 45 mm were taken and then mounted on the Monsanto Tensiometer machine with a loading speed of 2.5 mm/min and a beam of 500 kg. The graph was manually plotted by following the rise of the mercury along its column until failure occurred. Maximum cleavage load was recorded at the point of failure. Cleavage strength was calculated by using the following equation
(3)
Where P = Maximum load in Newton (N)
B = Width (mm)
Determination of compression strength parallel to the grain
Compression strength parallel to the grain was determined according to the standard procedure described by ISO 3787 [13]. Each test specimens measuring 20 x 20 x 60 mm was taken and loaded on a parallel grain basis to the Monsanto Tensiometer machine using a feeding speed of 0.635 mm/min and 2000 kg deflection beam. Then, the maximum crushing load was recorded by plotting the graph following the rise of the mercury in the column until failure occurs. The maximum crushing strength was then calculated from maximum crushing load and recorded in N/mm2. Crushing strength was calculated using the following formula:
(4)
Where P = Maximum load in Newton (N)
A = Cross-sectional area (mm2)
Determination of shear strength parallel to grain
Shear strength parallel to grain test was determined according to the standard procedure described by ISO 3347 [14]. Each test specimen measuring 20 mm x 20 mm x 20 mm was taken and mounted on the Monsanto Tensiometer machine with a 2000 kg deflection beam and a speed of 0.635 mm/min were used. Maximum shear strength was recorded graphically straight from the rise of the mercury along the column until failure occurred. Shear strength was calculated using the following equation:
(5)
Where P = Maximum load in Newton (N)
A = Area in shear (mm2)
Statistical Analysis
Data were analysed using SAS software Version 9.1 for Windows. Analysis of variance (ANOVA) was done to compare wood basic density, fibre length, MOE, MOR, Cleavage, compression and shear strength parallel to grain between Eucalypt hybrid clones. Significant clone means were separated by Duncan's Multiple Range Test (DMRT).

3. Results and Discussion

Wood basic density
Wood basic density ranged from 525.5 to 633.9 kgm-3 among the evaluated clones (Table 3). Clone GC 584 and GC 581 had significantly higher basic density values than GU 608 at Lushoto site. Wood of GC 940 and GC 15 at Kibaha site had significantly higher (p<0.05) basic density values than GC 167. However, there were no significant differences in basic densities between clones from Kwamarukanga and Tabora sites. On the other hand, the average fibre length ranged from 0.857 mm to 0.969 mm for all clones (Table 3). Fibre length differed significantly (p<0.05) between clones at Kwamarukanga, Kibaha and Tabora sites. However, no significant difference in fibre length was recorded for clones at Lushoto site.
The examination of table 3 show that the mean basic density of the studied clones varied between clones within a site. The differences might be a result of differences in the anatomy of wood such as vessel characteristics, type of cells, their proportions and arrangements as well as the accumulation of extractives in heartwood from individual hybrids [7, 15]. It may also be affected by intrinsic differences in growth rates of the individual trees sampled in Kenya [6]. The studied hybrid clones show basic density similar to other Eucalypt clones of 7-9 year-old [6, 7, 16, 17] in Kenya, Uganda, India and Brazil respectively. However, study results are slightly higher than those reported by Zanuncio et al. [18] for 7 year-old for E. urophylla clone. The present values are within the range reported for pulp and paper production i.e 480 to 650 kg m-3 [19, 20], 400 - 750kg m-3 timber for structural use [21] in Uganda and higher than 500 kgm-3 ideal for charcoal production [17, 22] in Brazil. According to FAO [23] wood with basic density less than 400 kg/m3 at 12% MC are termed as weak, 401 to 500 kg/m3 fairly strong; 501 to 640 kg/m3 strong; 641 to 800 kg/m3 very strong and more than 801 kg/m3 exceptional strong. Based on the FAO standards, all studied eucalypts clones are under the range of strong strength category indicating that they are potential for timber at age of 9 years.
Table 3. Wood basic density and fibre length of 9 year old Eucalypt hybrid clones
     
On the other hand, the fibre length values of Eucalypt hybrid clones as revealed in this study compares well with findings reported for E. grandis × E. urophylla hybrid trees [16, 24], E. grandis parent trees [25] from India, E. camaldulensis clones and other E. camaldulensis trees from Brazil [5] whose fibre length ranged between 0.95 mm to 1.06 mm. Findings in this study were higher than mean fibre length of 0.67 mm to 0.75 mm for Eucalypt hybrid clones [26] in India, 0.72 mm to 0.81 mm for Eucalypt clones and 0.70 mm for E. camaldulensis [27] in Morocco. According to Miranda et al. [20] and Jorge et al. [28] Eucalypt clones with fibre length between 0.87 to 1.04 mm are suitable for pulp and paper production, therefore wood of the clones studied are therefore suitable for pulp and paper production.
Mechanical properties
Modulus of Elasticity (MOE) and Modulus of Rupture (MOR)
The overall means of MOE and MOR across the four studied clones ranged from 8525.2 to 12710.4 Nmm-2 and 72.6 to 108.5 Nmm-2 respectively (Table 4). ANOVA results indicated significant (p<0.05) difference in MOE values for Eucalypt hybrid clones growing at Kibaha and Kwamarukanga sites. However, there were no significant differences in mean MOE for clones at Lushoto and Tabora sites. In addition, MOR differed significantly (p<0.05) between clones at Kwamarukanga site. No significant difference in MOR was recorded for clones at Lushoto, Kibaha and Tabora sites. GU 608 growing at Lushoto site showed higher MOR values than GC 581 and GC 584 while GT 529 growing at Kwamarukanga site showed higher MOR than GC 940 and GC 514. However, GC 940 at Kibaha site showed higher MOR values than GC 167 and GC 15 while GC 940 growing at Tabora had higher mean MOR values than GC 167 and GC 584.
Table 4. MOE and MOR of 9 year old Eucalypt hybrid clones in four sites
     
MOE of Eucalypt hybrid clones studied compare favourably with some Eucalypt hybrid clones and other Eucalyptus species. For instance, 7866 to 15080 Nmm-2 for Eucalypt clones and 8335 to 11892 Nmm-2 for E. grandis, E. tereticornis, E. camaldulensis and E. saligna for local landraces in Kenya [6]. Olufemi and Malami [29] reported MOE for E. camaldulensis (9048.49 to 19388.71 Nmm-2) and E. paniculata (12100 Nmm-2) in Nigeria. GT 529 and GC 581 had the highest MOR values, implying that they can withstand relatively higher bending stresses while in service. These findings were supported by Thelandersson and Hansson [30] who reported that MOR values of 93.4 Nmm-2 can withstand relatively higher bending stresses while in service. Based on Kityo and Plumptre, [21] classifications, MOE ranged from 6860 to 14700 N mm-2 and MOR of 39 to 132 Nmm-2 are suitable timber for structural applications. Wood of Eucalypt hybrid clones studied had MOE values within the specified ranges and thus can be used for making structural elements such as tie beams, rafters and purlins in house construction.
Radial and Tangential Cleavage
The mean cleavage strength values in the radial and tangential directions for Eucalypt hybrid clones from all studied sites are presented in Table 5. The overall mean radial cleavage strength ranged from 13.5 to 20.6 N mm-2 while tangential cleavage strength ranged from 14.9 to 22.0 Nmm-2. Wood of studied clones at Tabora site showed higher cleavage strength in radial and tangential directions for GC 584 and GC 15 respectively.
Table 5. Radial and Tangential Cleavage strength of wood of 9 year old Eucalypt hybrid clones from four sites
     
There were significant (p<0.05) differences in cleavage strength in the radial direction for wood of clones at Tabora site and significant (p<0.05) differences in tangential cleavage strength for wood from Lushoto and Tabora sites. Findings revealed that, tangential cleavage from Eucalypt hybrid clones wood was higher than in radial direction. This was probably due to the relationship between air-dry density and the cleavage strength of timber along the fibres [31]. The results were confirmed by Moya and Muñoz [32] and Ismaili et al. [33] that, cleavage strength at tangential direction possessed higher strength than radial direction for both green and an air-dry condition. The cleavage strength values obtained in this study are similar to those reported by Turinawe et al. [7], who documented cleavage strength ranging from 18 to 20 Nmm-2 for Eucalypt hybrid clones and 16 to 33 Nmm-2 for E. camaldulensis in Uganda.
Compression and shear strength parallel to grain
The results for compression and shear strength parallel to grain are presented in Table 6. The overall compression strength (CS) and shear strength values of studied Eucalypt hybrid clones across all sites ranged from 41.9 to 57.2 Nmm-2 and 7.7 to 13.7 Nmm-2 respectively. Significant (p<0.05) difference in CS was observed for clones at Tabora site. Wood from Lushoto site showed the lowest and highest mean CS values for GU 608 and GC 581 respectively. Wood of clones growing at Kwamarukanga site showed the lowest and highest mean CS values for GT 529 and GC 514 respectively. Wood from Kibaha site showed the lowest and highest mean CS values for GC 167 and GC 15 respectively. However, wood from Tabora site showed the lowest mean CS values for GC 15 and highest mean CS values for GC 584 and GC 940. ANOVA showed significant (p<0.05) differences in shear strength between Eucalypt hybrid clones in all sites. Clone GC 581 and GC 584 growing at Lushoto site showed significantly higher shear strength values than GU 608. Clone GT 529 showed significantly higher mean shear strength values than GC 514 and GC 940 for Kwamarukanga site while GC 940 showed significantly higher mean shear strength values than GC 15 and GC 167 at Kibaha site. GC 15 and GC 584 showed significantly higher mean shear strength values than GC 940 at Tabora site.
Table 6. Compression and Shear strength parallel to grain of 9 year old Eucalypt clones
     
Eucalypt hybrid clones have shown compression strength similar to those reported by Moya and Muñoz [32]; Acosta et al. [34]. The mean compression strength of this study was somewhat greater than those reported previously by Lima et al. [35] for 8 year old Eucalypt clones and 20 year old E. camaldulensis in Nigeria [36]. According to Muga et al. [6], Eucalypt hybrid clones have significantly higher compression strength values than E. grandis and E. tereticornis progenies in Kenya. The results showed significant shear strength between clones within a site. This could be attributed to genetic differences and other localized site factors. Madsen [37] found that, the shear strength does appear to be affected somewhat by moisture content between green and air-dry condition. Shear strength values obtained in this study are in keeping with results reported by Santos et al. [17]; Lima and Garcia [38] with shear strength values ranged from 10.7 to 13.8 Nmm-2 for E. grandis and E. resinifera. Wood from GC 584 and GC 581 at Lushoto site and GC 940 at Kibaha site have good shear values implying that they could be used as substitutes for structural purposes where toughness is desired.

4. Conclusions

There were significant variations in wood basic density between clones at Lushoto and Kibaha sites while at Kwamarukanga and Tabora sites showed no significant variation. Significant variation in fibre length was observed for Eucalypt hybrid clones at Kibaha, Kwamarukanga and Tabora sites while Lushoto site showed no significant difference. On the other hand, mechanical properties values for the studied Eucalypt hybrid clones meet the minimum requirements needed for different structural applications. Wood properties values obtained in this study placed Eucalypt hybrid clones wood at a better position of suitability enabling the wood to compare favourably with other Eucalypt clones and Eucalyptus species for pulp and paper and timber for structural use. Therefore, it can be concluded that, Eucalypt hybrid clones should be considered as source of raw materials for pulp and paper production, timber for structural use and for structural elements.

References

[1]  Mwaniki, F., Muluvi, G., Gichuki, C., Oeba, V.O. and Kanyi, B. (2009). Development of non-mist vegetative propagation protocol for Eucalyptus Hybrid Clones. Journal of East African Natural Resources Management 3(1): 283–295.
[2]  Sprague, J. R., Talbert, J.T., Jett, J.B. and Bryant, R.L. (1983). Utility of the Pilodyn in selection for mature wood specific gravity in loblolly pine. Forest Science, 29, 696–701.
[3]  Zobel, B.J., and Van Buijtenen, J.P. (1989). Wood variation: Its causes and control. Springer–Verlag, New York.
[4]  FPL. (2010). Wood handbook -Wood as an engineering material. General Technical Report FPL-GTR-190. U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. Madison.
[5]  Quilhó, T., Miranda, I. and Pereira, H. (2006). Within-tree variation in wood fibre biometry and Basic density of the Urograndis Eucalypt hybrid (eucalyptus grandis × E. urophylla). IAWA Journal 27 (3): 243 – 254.
[6]  Muga, M.O., Muchiri, M.N. and Kirongo, B.B. (2009). Variation in Wood Properties of Eucalyptus Hybrid Clones and Local Landraces Grown in Kenya. Journal of East African Natural Resources Management 3(1):215–227.
[7]  Turinawe, H., Mugabi, P. and Tweheyo, M. (2014). Density, calorific value and cleavage strength of selected hybrid Eucalypts grown in Uganda. Ciencia tecnología 16(1):13–24.
[8]  Bal, B.C., and Bektaş, I. (2014). Some mechanical properties of plywood produced from Eucalyptus, Beech, and Poplar Veneer. Maderas. Ciencia y tecnología 16(1): 99–108.
[9]  BS 373. (1957). Methods of testing small clear specimen of timber. British Standard Institution, 2 Park Street, London, United Kingdom.
[10]  ISO 3349. (1975). Wood-Determination of modulus of elasticity in static bending, International organization for standardization. Switzerland.
[11]  ISO 3133. (1975). Wood-Determination of ultimate strength in static bending, International organization for standardization. Switzerland.
[12]  Panshin, A.J. and De Zeeuw, C. (1980). Textbook of wood technology, 4th edition. McGraw-Hill, New York, USA.
[13]  ISO 3787. (1976). Wood-Test method - Determination of ultimate stress in compression parallel to grain, International organization for standardization. Switzerland.
[14]  ISO 3347. (1976). Wood-Determination of ultimate shearing stress parallel to grain, International organization for standardization. Switzerland.
[15]  Panshin, A.J., and De Zeeuw, C. (1970). Textbook of wood technology. Mc Graw Hill Book Co. Ltd., New York.
[16]  Carvalho, M.A. and Nahuz, M.A. (2001). The evaluation of the Eucalyptus grandis × urophylla hybrid wood through the production of small dimension sawnwood, pulpwood and fuelwood. Scientia Forestalis 59:61–76.
[17]  Santos, R.C.D., Carneiro, A.D.C.O. and Castro, A.F.M. (2011). “Correlation of quality parameters of wood and charcoal of clones of Eucalyptus,” Forest Sciences 90:221–230.
[18]  Zanuncio, A.J.V., Monteiro, T.C., Lima, J.T., Andrade, H.B. and Carvalho, A.G. (2013). Drying biomass for energy use of Eucalyptus urophylla and Corymbia citriodora logs. BioResources 8(4):5159–5168.
[19]  Ikemori, Y.K., Martins, F.C.G. and Zobel, B.J. (1986). The impact of accelerated breeding on wood properties. In 18th IUFRO World Conference Division 5: Forest Products. Ljubljana, Yugoslavia. 358–368p.
[20]  Miranda, I., Almeida, M.H. and Pereira, H. (2001). Provenance and site variation of wood density in Eucalyptus globulus Labill. at harvest age and its relation to a non-destructive early assessment. Forest Ecology and Management 149:235–240.
[21]  Kityo, P.W. and Plumptre, R.A. (1997). The Uganda Timber User’s Handbook. A guide to better timber use. Common Wealth Secretariat London.
[22]  Trugilho, P.F., Lima, J.T., Mori, F.A. and Lino, A.L. (2001). “Evaluation of Eucalyptus clones for charcoal production,” Cerne 7(2):104–114.
[23]  FAO (2010). Construction materials. Food and Agriculture Organization of Unites Nations. Chapter 5. Pp 45 – 91. Http://www.fao.org/decrep/015/i2433e/2433ec.pdf.
[24]  Carvalho, M. A., and Nahuz, M. A. (2001). The evaluation of the Eucalyptus grandis × urophylla hybrid wood through the production of small dimension sawnwood, pulpwood and fuelwood. Scientia Forestalis 59: 61–76.
[25]  Bhat, K.M., Bhat, K.V. and Dhamodaran, T.K. (1990). Wood density and fibre length of Eucalyptus grandis grown in Kerala, India. Wood Fibre Science 22:54–61.
[26]  Dutt, T. and Tyagi, C.H. (2011). Comparison of various Eucalyptus species for their morphological, chemical, pulp and paper making characteristics. Indian Journal of chemical technology 18:145–151.
[27]  El Moussaouit, M., Barcha, B., Alves, E.F. and Francis, R.C. (2012). Kraft pulping characteristics of three Moroccan Eucalypti. Part 1. Physical and chemical properties of woods and pulps. BioResources 7(2):1558–1568.
[28]  Jorge, F., Quilhó, T. and Pereira, H. (2000). Variability of fibre length in wood and bark in Eucalyptus globulus. IAWA Journal 21:41–48.
[29]  Olufemi, B., and Malami, A. (2011). Density and bending strength characteristics of North Western Nigerian grown Eucalyptus camaldulensis in relation to utilization as timber. Research Journal of Forestry 5(2):107–114.
[30]  Thelandersson, S., and Hansson, M. (1999). Reliability of Timber Structural Systems Effects of Variability and In Homogeneity. Lund University of Technology, Division of Structural Engineering, Sweden.
[31]  Wallis, N.K. (2010). Australian timber handbook, Halstead Press, Sydney, Australia.
[32]  Moya, R., and Muñoz, F. (2010). 'Physical and mechanical properties of eight fast growing plantation species in Costa Rica'. Tropical Forest Science 22(3):317–328.
[33]  Ismaili, G., Bakar, B.H.A., Duju, A., Rahim, K.K.A., Openg, I., Ismaili, Z. and Ismaili, S. (2013). Domination of Grain Bearing on the Strength Properties of Engkabang Jantong as Fast Growing Timber in Sarawak. Iranica Journal of Energy and Environment 4(3):311–315.
[34]  Acosta, M.S., Marco, M., Piter, J.C., Zitto, M.A.S., Villalba, D.I. and Carpineti, L. (2007). “Physical and mechanical properties of Eucalyptus grandis x E. tereticornis hybrid grown in Argentina”, IUFRO All Division 5 Conference, Taiwan. 35pp.
[35]  Lima, J.T., Breese, M.C. and Cahalan, C.M. (1999). Variation in compression strength parallel to the grain in Eucalyptus clones. Proceedings of the Fourth International Conference. 14-16 July 1999, Development of Wood Science, Wood Technology and Forestry, Missenden Abbey, UK. 28 – 36pp.
[36]  Malami, A.A. and Olufemi, B. (2013). Influence of Compression Stresses on Timber Potentials of Plantation Grown Eucalyptus camaldulensis Denhn in North-Western Nigeria. Nigerian Journal of Basic and Applied Science 21(2):131–136.
[37]  Madsen, B. (1992). Structural behaviour of timber. Timber Engineering Ltd., Canada.
[38]  Lima, I.L., and Garcia, J.N. (2011). Effect of fertilization on mechanical properties of Eucalyptus grandis. Ciência Florestal 21:601–60.