Wood and Cellular Properties of Four New Hevea Species

M. A. Norul Izani and S. Mohd. Hamami Universiti Putra Malaysia, Sarawak, Malaysia

Abstract

Increasing demand for timber and the depletion of natural forests have encouraged the utilization of many less popular species. An understanding of wood properties and behaviour is important to evaluate the potential of these species to produce high quality end products. This study determined the anatomical and physical properties of Hevea species viz H. pauciflora, H. guianensis, H. spruceana, H. benthamiana and H. brasiliensis. Each sample tree was cut into three different height portions (bottom (B), middle (M) and upper (T) parts) and two radial samples (outer (O) and inner (I)). The H. brasiliensis clone, RRIM 912, exhibited the longest fibre length of 1214 m, followed by H. benthamiana (HB, 1200 m), H. pauciflora (HP, 1189 m), H. spruceana (HS, 1158 m) and H. guianensis (HG, 1145 m). Fibre length has a positive correlation with specific gravity. The largest fibre diameter (24.9 m) and lumen diameter (12.5 m) were recorded in H. guianensis. The highest moisture content was obtained from H. spruceana (64.34%) compared to the lowest in the H. brasiliensis clone RRIM 912 (60.01%). A higher moisture content is normally associated with lower strength. Overall, the properties of clone RRIM 912 were found to be comparatively better because of its higher strength due to longer fibre length, thicker cell walls and higher specific gravity than the other Hevea species. Therefore, this species could be used as a general utility timber.

Keywords: wood anatomy, forest products, rubber trees, Hevea species, moisture content

Proceedings of the FORTROP II: Tropical Forestry Change in a Changing World, 17-20 November 2008, Kasetsart University, Bangkok, Thailand 2 FORTROP II: Tropical Forestry Change in a Changing World

Introduction

Rubberwood is a valuable timber species for furniture manufacture on a commercial scale due to its beautiful, light and even-coloured texture, comparable strength and easy machining and processing properties (Lew and Sim, 1983; Chew, 1993). In general, the rubber tree species is easy to recognize because it is woody, medium to large sized and presents a typical leaf shedding and renovation pattern (Wycherley, 1992). In 2000, 80% of wooden furniture in Malaysia was made of rubberwood. The rubberwood furniture industry has seen tremendous achievements (Mohammad Nazuri et al., 2000). For decades, Malaysia has been acknowledged as the world’s leading supplier of natural rubber.

Thus, rubberwood (Hevea brasiliensis) has been well documented since the 1970’s, and it now is desirable to document the properties of other Hevea species in order to compensate for the shortage of H. brasiliensis in the downstream wood processing industries. They are capable of turning out a wide range of high quality products. Significant research has been carried out to identify new clones or species that will increase timber yield. Other than H. brasiliensis, H. nitida has been found to have potential to produce nine times more timber than the RRIM 600 clone (Najib et al., 1997). Since these various rubberwood species are in the same genus as H. brasiliensis, it is expected that other Hevea species may also have almost the same or even better properties than H. brasiliensis.

An understanding of the anatomical properties and wood structure is important because it can encompass the density, mechanical and strength properties and determine the characteristics of potential products. The most common anatomical properties studied are: the proportion of early and latewood, fibre length, cell wall thickness, lumen diameter and the parenchyma proportion (Desch and Dinwoodie, 1983). Fibre length, an important aspect of fibre morphology, is related to the mechanical strength and longitudinal shrinkage and is known to affect the strength properties of paper (Dinwoodie, 1981). Fibre cross-sectional dimensions such as fibre diameter, lumen diameter and wall thickness affect some properties such as strength, shrinkage and swelling, permeability, gluing and machining characteristics (van Buijtenen, 1969).

Volume 11: Wood Products and Bio-Based Materials 3

Introduction Among the physical factors that influence strength, the most important ones are specific gravity, moisture content, shrinkage and swelling (Lavers, 1969). The specific gravity of wood is the single most important physical characteristic, to which most mechanical properties of wood are closely correlated. If the specific gravity increases, the strength of wood as well as the stiffness also increases. In the utilization of rubberwood, the study of its structure is important as it establishes the variation in the properties of the wood (Lim and Ani, 1994).

This study was conducted to determine the differences in rubberwood properties from five different Hevea sp. i.e. clone RRIM 912 from Hevea brasiliensis, H. pauciflora, H. guainensis, H. spruceana and H. benthamiana.

Materials and Methods

Sample Collection

The five rubberwood species used in this study were H. pauciflora (HP), H. guainensis (HG), H. spruceana (HS), H. benthamiana (HB) and H. brasiliensis clone RRIM 912. Trees aged 15 years were felled from a plantation of the Rubber Research Institute Malaysia (RRIM) at Bandar Penawar, Johor. After felling, the bole of each tree was cut into three lengths of 2 m. In each length, a disc was taken and labeled as either from the top, middle or bottom part. Discs were wrapped in plastic to avoid any changes in moisture content.

Anatomical Properties

This phase covered the study of fibre morphology and cellular structure along the stem of the rubberwood. Discs from each height were cut into strips with a width of 6 cm across the centre. They were then cut into cubes of 2 cm x 6 cm containing both sapwood and heartwood areas. Each cube was further cut into a 1 cm x 2 cm x 2 cm specimen for slide preparation to determine the cellular structure in the three different planes of a cross, tangential and radial section. Samples of thin sectional slides and macerated wood elements were prepared for anatomical assessment in accordance with the Botanical Microtechnique (Berlyn and Miksche, 1976). 4 FORTROP II: Tropical Forestry Change in a Changing World

The microscopic structure of each species was examined using an optical microscope, projection microscope and a scanning electron microscope (Image Analyser) for the measurement of vessel diameter and frequency, fibre diameter and length, lumen diameter, cell wall thickness and the proportion of fibres and rays.

Physical Properties

Samples for the physical test were cut from the discs of the trees. The samples for physical tests were cut in accordance with ISO 3129-1975 (E) – Wood Sampling Methods and General Requirements for Physical and Mechanical Tests (ISO, 1937). For each small block, the following experiments were carried out: 1) moisture content based on green condition; 2) specific gravity based on dry weight; 3) shrinkage under air dry and oven dry conditions in three different directions (radial, tangential and longitudinal).

All the samples were analyzed using analysis of variance (ANOVA) and significant differences between mean values using a least significant difference test (LSD) at p=0.05.

Results and Discussions

Anatomical Properties

Figure 1 shows that the fibre length between the upper and middle parts was not significantly different. Roslan (1998) noted that the mean fibre length of rubberwood fibres was 1.10 mm. The length of fibres usually varies according to tree height, with the middle part possessing the longest fibres, followed by the upper and bottom parts, respectively. The results showed that the fibre length of the rubberwood species in the current study increased from the bottom to the top of the tree. Dinwoodie (1981) noted that fibre length could be considered as the most important aspect in determining the quality of wood because it related to mechanical strength and shrinkage, while also influencing the paper strength properties. Volume 11: Wood Products and Bio-Based Materials 5

Outer Inner

1300 1274 1256 1250 1223 1222 1211 1223 1197 1183 1200 1183

Physical Properties 1150 1129 1097 1100 1090 1097

Fibre length (m) Fibre length Fibre length (m) Fibre length 1050

1000 950 HP HG HB HS RRIM HP HG HB HS RRIM Growth types

FFigureigure 1 Mean fibre length for different species of rubberwood in two radial positions.

H. guianensis had the highest value for fibre diameter with 24.9 m (Table 1).

Figure 2 shows that there was a significant difference between species for Results and Discussions different radial positions. According to Sekhar (1989) and Peel and Peh

(1960), the mean fibre diameter of rubberwood was about 22.0 m. Ashaari Anatomical Properties (1980) noted that rubberwood fibre diameter decreased in the outer pith and

increased in the inner pith. A higher value for fibre diameter will increase the strength properties of the wood (Mohd Izham, 2001).

TableTable 1 Mean values on the anatomical properties of rubberwood.

PPropertyroperty SpeciesSpecies PortionPortion RadialRadial positionposition Fibre length 1214a (RRIM 912) 1257a (T) 1220a (O) 1200a (HB) 1234a (M) 1144b (I) 1189a (HP) 1056b (B) 1158b (HS) 1145b (HG) Fibre diameter 24.9a (HG) 24.5a (T) 24.3a (O) 24.3a (HP) 24.3a (M) 23.7b (I) 23.7b (HS) 23.3b (B)

6 FORTROP II: Tropical Forestry Change in a Changing World

Table 1 (Cont.)

Property Species Portion Radial position Fibre diameter 23.6b (HB) 23.5b (RRIM 912) Lumen diameter 12.5a (HG) 11.73a (T) 11.64a (O) 11.5a (HP) 11.52a (M) 11.29a (I) 11.4a (HB) 11.14a (B) 11.3a (HS) 10.4b (RRIM 912) Cell wall thickness 6.51a (HS) 6.35a (M) 6.34a (O) 6.37a (RRIM 912) 6.32a (T) 6.16a (I) 6.17b (HG) 6.08b (B) 6.13b (HB) 6.08b (HP) Vessel diameter 155.3a (RRIM 912) 162.4a (T) 143.5a (O) 154.7a (HS) 157.1b (M) 134.4b (I) 139.4b (HB) 101.3c (B) 138.4b (HP) 122.6b (HG) Vessel frequency 2.61a (HG) 2.57a (T) 3.18a (I) 2.48a (HP) 2.52a (M) 2.37b (O) 2.47a (HB) 2.34a (B) 2.46a (HS) 2.33b (RRIM 912) Proportion of fibres 55.1a (HB) 51.2a (B) 49.5a (O) 49.9b (HP) 49.4b (M) 48.9b (I) 48.6b (RRIM 912) 47.2c (T) 47.5b (HG) 45.1c (HS) Proportion of rays 33.3a (RRIM 912) 32.1a (B) 31.7a (O) 32.8a (HP) 31.9a (M) 31.4a (I) 31.5b (HB) 30.8b (T) 30.4b (HG) 29.8c (HS)

Note: Means in each column followed by the same letters are not significantly different at p>0.05. HP = H. pauciflora HG = H. guianensis HB = H. benthamiana HS = H. spruceana RRIM = H. brasiliensis clone RRIM 912 T = Top, M = Middle, B = Bottom, I = Inner, O = Outer

Volume 11: Wood Products and Bio-Based Materials 7

Table 1 Outer Inner Property Species Portion Radial position 27 25.8 26 24.7 25 24.9 24.3 24.2 23.9 24 23.5 22.6 23 22.7 22.1 22 Fibre diameter (m) (m) diameter Fibre (m) diameter Fibre 21 20 HP HG HB HS RRIM Growth types

FFigureigure 2 Mean fibre diameter for different species of rubberwood in two radial positions.

The lumen diameter for H. pauciflora, H. benthamiana and H. spruceana was similar, with a value of 11.5, 11.4 and 11.3 m, respectively. This agreed well with the research of Norhayati (1995), which found that the lumen diameter was in the range of 10.00 to 12.00 m. The results indicated that the mean lumen diameter increased with height, while results for the radial zones showed that the mean lumen diameter increased from the pith to bark (Figure 3). When the lumen diameter is large, the percentage of shrinkage is lower due to the lumen content affecting shrinkage. The specific gravity is also lower if the lumen diameter is large.

H. pauciflora had the thinnest fibre walls (6.08 m) compared with the other species (Table 1). There was no significant difference in cell wall thickness between the outer and inner radial positions (Figure 4). Fibres are important as supporting elements in tree. Specific gravity, shrinkage and the strength of the tree are also related to the cell wall thickness.

8 FORTROP II: Tropical Forestry Change in a Changing World

Outer Inner

14 13.1 13.2 12.4 12.4 11.4 11.7 12 12 10.9 10.7 9.69 10 9.24 8

6

4 Lumen diameter (m) Lumen diameter (m) Lumen diameter 2

0 HP HG HB HS RRIM Growth types

FFigureigure 3 Mean lumen diameter for different species of rubberwood in two radial positions.

Outer Inner

7.0 6.76 6.8 6.63 6.6 6.48 6.47 6.36 6.4 6.36 6.2 6.11 5.91 6.0 5.81 5.86 5.8 5.67 5.6 5.4 Cell wall thickness (m) (m) thickness wall Cell Cell wall thickness (m) (m) thickness wall Cell 5.2 5.0 HP HG HB HS RRIM

Growth types

FFigureigure 4 Mean cell wall thickness for different species of rubberwood in two radial positions. Volume 11: Wood Products and Bio-Based Materials 9

The results showed that the mean values were higher for the outer samples than the inner samples (Figure 5). The value of mean vessel diameter increased from the stump upwards to the branches though this pattern of increment was not consistent (Roslan, 1998).

The vessel frequency for H. pauciflora, H. guianensis, H. benthamiana and H. spruceana was similar, with a value of 2.60, 2.48, 2.47 and 2.46 vessels/mm2 respectively (Table 1). Sekhar (1989) noted that the mean vessel frequency for rubberwood was 3 to 4 vessels/mm2. The results showed that the mean vessel frequency decreased from pith to bark (Figure 6).

The highest percentage of fibres was recorded in H. benthamiana (55.1%), followed by H. pauciflora (49.9%), RRIM 912 (48.6%), H. guianensis (47.5%) and H. spruceana (45.1%).

The highest percentage of rays was recorded in RRIM 912 (33.3%), while Figure 3 H. spruceana showed the lowest percentage (29.8%) of fibres. Haygreen and Bowyer (1982) stated that rays play an important role in restraining dimensional change in the radial direction, and their presence is partially responsible for the fact that upon drying, wood shrinks less radially than tangentially.

Outer Inner 161.1 180 161.1 159.1 162.5 164.9 160 160 146.8 120.8 126.7 138.1 140 120.8 126.7 138.1 117.7 123.6 120 100 80 60 40 Vessel diameter (m) diameter Vessel (m) diameter Vessel 20 0 HP HG HB HS RRIM HP HG HB HS RRIM Growth types Figure 4

FFigureigure 5 Mean vessel diameter for different species of rubberwood in two radial positions. 10 FORTROP II: Tropical Forestry Change in a Changing World

Outer Inner

3.5

2.97 2.84 3.0 2.59 2.65 2.59 2.34 2.55 2.51 2.5 2.31 2.16 ) ) 2.11 2 2 2.0

1.5 1.5 (no./mm (no./mm 1.0 Vessel frequency frequency Vessel Vessel frequency frequency Vessel 0.5

0 HP HG HB HS RRIM Growth types

FigureFigure 6 Mean vessel frequency for different species of rubberwood in two radial positions.

PhysicalPhysical PropertiesProperties

The highest moisture content was obtained from H. spruceana (64.34%), while the lowest was recorded by RRIM 912 (60.01%). Moisture content is very important in the drying process as well as when timber is transported or traded by green weight (Roslan, 1988). Higher moisture content is normally associated with lower strength. The results indicated that there were significant differences in moisture content between the upper part, compared to the middle and bottom parts of the tree. (Table 1) The bottom part should have lower moisture content than the other parts as the specific gravity increases from the bottom towards the upper part of the tree (Lavers, 1969; Findlay, 1975). Figure 7 shows the mean moisture content in two radial positions.

The results showed that there were no significant differences in specific gravity between Hevea species. The specific gravity has a great effect on growth performance in wood, indicating the strength of a particular wood. Dinwoodie (1981) stated that the specific gravity or density of wood is important in research because it is the single most important criteria for Volume 11: Wood Products and Bio-Based Materials 11

good strength properties and is very important in determining the minimum strength value for timber. Armstrong et al. (1984) agreed, based on the well- known fact that there are direct relations between the strength properties of wood and its specific gravity or density. In general, the heaviest timber is at the base of the tree, with the mass decreasing further up the tree, which is confirmed by Table 2. Figure 8 shows the mean specific gravity for two radial positions.

Outer Inner

68 67.07

66 64.83 63.86 64 62.79 62.84 62.79 62.7 61.43 62 61.43 59.93 60 Figure 6 58.54 58 Moisture content (%) Moisture content Moisture content (%) Moisture content 56

54 Physical Properties HP HG HB HS RRIM

Growth types

FFigureigure 7 Mean moisture content for different species of rubberwood in two radial positions.

TTableable 2 Mean values on the physical properties of rubberwood.

PPropertyroperty SpeciesSpecies PortionPortion RadialRadial positionposition Moisture content 64.34a (HS) 62.25a (B) 62.61a (I) (green condition) 63.80b (HG) 62.22a (M) 61.20a (O) 60.69c (HP) 60.24b (T) 60.68c (HB) 60.01c (RRIM 912) Specific gravity 0.60a (RR) 0.60a (B) 0.59a (O) 0.59a (HB) 0.59a (M) 0.57a (I) 0.59a (HS) 0.57a (T) 0.58a (HP)

12 FORTROP II: Tropical Forestry Change in a Changing World

Table 2 (Cont.)

Property Species Portion Radial Position 0.57a (HG) Tangential shrinkage 1.61a (HG) 1.46a (T) 1.45a (I) (AD) 1.48b (HS) 1.35b (M) 1.39b (O) 1.37c (HB) 1.29b (B) 1.36c (RRIM 912) 1.35c (HP) Radial shrinkage (AD) 0.81a (HG) 0.89a (T) 0.63a (I) 0.79a (HS) 0.69b (M) 0.55b (O) 0.61b (HB) 0.68b (B) 0.59c (RRIM 912) 0.55c (HP) Longitudinal 0.31a (HG) 0.37a (T) 0.28a (I) shrinkage (AD) 0.30a (HS) 0.31a (M) 0.25a (O) 0.28b (HB) 0.29a (B) 0.28b (RRIM912) 0.25b (HP) Tangential shrinkage 3.62a (HG) 3.12a (T) 3.03a (I) (OD) 3.44b (HS) 2.91b (M) 3.16b (O) 3.16c (HB) 2.85b (B) 3.11c (RRIM 912) 3.07c (HP) Radial shrinkage 1.64a (HG) 1.78a (T) 1.78a (I) (OD) 1.55a (HS) 1.39b (M) 1.56b (O) 1.34b(HB) 1.23b (B) 1.28c (RRIM 912) 1.21c (HP) Longitudinal 0.78a (HG) 0.88a (T) 0.86a (I) shrinkage (OD) 0.77a (HS) 0.71a (M) 0.79a (O) 0.74a (HB) 0.67a (B) 0.73a (RRIM 912) 0.71a (HP)

Note: Means in each column followed by the same letters are not significantly different at p>0.05. HP = H. pauciflora HG = H. guianensis HB = H. benthamiana HS = H. spruceana RRIM = H. brasiliensis clone RRIM 912 T= Top, M = Middle, B = Bottom, I= Inner, O = Outer

Volume 11: Wood Products and Bio-Based Materials 13

Table 2

Property Species Portion Radial Position Outer Inner 0.64 0.62 0.62 0.62 0.61 0.600.60 0.60 0.60 0.58 0.58 0.58 0.57

0.56 0.55 Specific gravity Specific gravity Specific gravity 0.54

0.52

0.50 HP HG HB HS RRIM

Growth types

FFigureigure 8 Mean specific gravity for different species of rubberwood in two radial positions.

H. guianensis had the highest percentage of tangential shrinkage under air dry conditions (1.61%), followed by H. spruceana (1.48%), H. benthamiana (1.37%), RRIM 912 (1.36%) and H. pauciflora (1.35%). The results showed that the tangential shrinkage was greatest followed by radial and longitudinal shrinkage (Figures 9 and 10). This is supported by Kollman and Cote (1968), who noted that the shrinkage was not the same in different directions as a result of the straining influence of the wood rays in the radial direction due to the different helical arrangement of fibrils in the radial and tangential cell walls. The shrinkage was higher for the inner samples compared to the outer samples in all three directions (tangential, radial and longitudinal). Khoo et al. (1991) discovered that shrinkage in Hevea wood could be considered quite low with radial and tangential shrinkage averaging 0.83 and 1.22%, respectively, from green to air dry conditions. Under oven dry conditions, H. guianensis showed the highest percentage of tangential shrinkage (3.62%), followed by H. spruceana (3.44%), RRIM 912 (3.16%), H. pauciflora (3.11%) and H.benthamiana (3.07%). The results showed that tangential shrinkage was greater than radial shrinkage, while longitudinal shrinkage was very small. 14 FORTROP II: Tropical Forestry Change in a Changing World

tangential radial longitudinal

1.80 1.61 1.60 1.35 1.48 1.40 1.37 1.36 1.20 1.00 0.80 0.81 0.79 0.59 0.61 0.60 0.55 0.28 0.31 0.28 0.25 0.30 Shrinkage (%) 0.28 0.25 0.30 Shrinkage (%) 0.40 0.20 0.00 HP HG HB HS RRIM 912

Species

FigureFigure 9 Distribution of shrinkage (radial, tangential, longitudinal) under air dry conditions for different species of rubberwood.

tangential radial longitudinal

4.00 3.62 3.50 3.44 3.11 3.07 3.16 3.00 2.50 2.00 1.64 1.55 1.50 1.28 1.21 1.34 Shrinkage (%) Shrinkage (%) 1.00 0.71 0.77 0.78 0.74 0.73 0.50 0.00 HP HG HB HS RRIM 912

Species

FigureFigure 1100 Distribution of shrinkage (radial, tangential, longitudinal) under oven dry conditions for different species of rubberwood.

Volume 11: Wood Products and Bio-Based Materials 15

Table 3 compares the five species of Hevea wood. The results indicated that RRIM 912 had the longest fibre length of all the Hevea species. Due to having the thickest cell walls and a high specific gravity, RRIM 912 has better potential to be used for solid wood. The higher proportion of thick wall fibres means that the strength of the wood will also be higher. However, H. guianensis showed lower wood quality properties than RRIM 912 because it recorded the shortest fibre length and largest lumen diameter, which contribute to greater longitudinal shrinkage. The values for H. pauciflora are much closer to H. guianensis in all anatomical properties measured.

Table 3 Comparison of the anatomical features and physical properties of five different species of Hevea wood.

Figure 9 Properties HP HG HB HS RRIM Fibre length (m) 1189 1145 1200 1158 1214 Fibre diameter (m) 24.3 24.9 23.6 23.7 23.5 Lumen diameter (m) 11.5 12.5 11.4 11.3 10.4 Cell wall thickness (m) 6.07 6.17 6.13 6.51 6.37 Vessel diameter (m) 138.4 122.6 139.4 154.7 155.3 Vessel frequency (no./mm2) 2.48 2.61 2.47 2.46 2.33 Percentage of fibres (%) 49.9 47.5 55.1 45.1 48.6

Percentage of rays (%) 32.8 30.4 31.5 29.8 33.3

Moisture content (%) 60.69 63.80 60.68 64.34 60.01

Specific gravity 0.58 0.57 0.59 0.59 0.60 Shrinkage Tangential* (%) 1.35 1.61 1.37 1.48 1.36 Radial* (%) 0.55 0.81 0.61 0.79 0.59 Longitudinal* (%) 0.25 0.31 0.28 0.30 0.28

Tangential# (%) 3.07 3.62 3.16 3.44 3.11

Radial# (%) 1.21 1.64 1.34 1.55 1.28

Longitudinal# (%) 0.71 0.78 0.74 0.77 0.73

Figure 10 Note: HP = Hevea pauciflora HG = Hevea guianensis HB = Hevea benthamiana HS = Hevea spruceana RRIM = H. brasiliensis clone RRIM 912 * = shrinkage at air dry conditions # = shrinkage at oven dry

16 FORTROP II: Tropical Forestry Change in a Changing World

Conclusions

An understanding of the anatomical properties and wood structure of Hevea wood is important because it helps to relate the density, mechanical and strength properties to the characteristics of potential products. Overall, the properties of clone RRIM 912 were found to be comparatively better because of higher strength due to longer fibre length, thicker cell walls and higher specific gravity than the other 4 Hevea species. Therefore, this species can be inferred to have potential as a general utility timber.

Acknowledgements

The author wishes to express her sincere thanks to all Faculty of Forestry (UPM) staff for their contributions and support throughout the study. This project was also made possible through the cooperation of officers at the Rubber Research Institute of Malaysia (RRIM).

References

Armstrong, J.P., C. Skaar and C. deZeeuw. 1984. The effect of specific gravity on several mechanical properties of some world woods. Wood Science and Technology 18: 137-146. ISO. 1975. International Standard, ISO 3129-1975 (E): Wood sampling methods and general requirements for physical and mechanical tests. International Organization for Standardization. Geneva, Switzerland. Ashaari, H.A. 1980. Variation in Certain Wood Properties of Rubber Trees (Hevea brasiliensis Muell Agr.). M.S. Thesis. Louisiana State University. Berlyn, G.P. and J.R.P. Miksche. 1976. Botanical Microtechnique and Cytochemistry. The Iowa State University Press, Ames, Iowa. Chew, L.T. 1993. Rubberwood development in Malaysia. Paper presented at the International Forum on Investment Opportunities in the Rubberwood Industry. 20-22 September 1993. Kuala Lumpur, Malaysia. Desch, H.E. and J.M. Dinwoodie. 1983. Timber: It’s Structure, Properties and Utilization. 5th Edition. Lowe and Brydone (Printers) Ltd., Theford, Norfolk. Volume 11: Wood Products and Bio-Based Materials 17

Conclusions Dinwoodie, J.M. 1981. Timber Its Structure, Properties and Utilization. Timber Press, Forest Grove, Oregon, USA. Findlay, W.P. 1975. Timber: Properties and Uses. Crosby Lochwood Staples, Britain. Haygreen, J. G. and J. L. Bowyer. 1982. Forest Products and Wood Science - An Introduction. Iowa State University Press, Ames. Kollmann, F.F.P., and W.A. Cote,Jr. 1968. Principles of Wood Science and Technology Solid Wood. Volume 1. Springer-Verlag, Berlin Heidelberg, New York. Lavers, G.M. 1969. The Strength of Timbers Bulletin No.5. 2nd ed. Metric Acknowledgements Units, London. Lew, W.H. and H.C. Sim. 1983. Rubberwood Present and Potential Utilization. In L.T. Hong, ed. Proceedings of Rubberwood Utilization Seminar 15th June 1982. Kuala Lumpur. FRIM Report No.28. Kepong, Malaysia. Lim, S.C. and A. Sulaiman. 1994. Structure and Characteristics of Rubberwood. Rubberwood Processing and Utilization. Forest References Research Institute, Kepong Malaysia. Mohammad Nazuri, H., A. Zaleha and L.M.H., Noor. 2000. Supply, demand and pricing for rubberwood. Paper Presented at the Seminar on “Rubber Forest Plantation: Smart Partnership towards Rubber Forest Development”. 22 May 2000. Sungai Buluh, Selangor, Malaysia. Mohd Izham, Y. 2001. Juvenility of Rubberwood at Different Age. M.S. Thesis, Faculty of Forestry, UPM. Najib, L.A., M. Johari, M.H., A. Ghani Ibrahim, Y.M. Dan, B. Mahdan and A.W. Mahmud. 1997. Viability of Hevea Plantation for Wood Production. Paper presented at the Seminar on Commercial Cultivation of Teak, Sentang, Acacia and Hevea for Timber. 9 January 1997, Kuala Lumpur, Malaysia. Norhayati, N. 1995. Anatomical properties of rubberwood from three clones and two age groups. Unpublished final year project report. Faculty of Forestry, UPM. Peel, J.D. and T.B. Peh. 1960. Para rubberwood (Hevea brasiliensis Muell Arg.) for pulp and paper manufacturer. An Account of Laboratory Experiment. Research Pamphlet No 34. Roslan, M. 1998. Juvenility in Rubberwood (Hevea brasiliensis) and its Relation with the Physical and Mechanical Properties. M.S. Thesis, Faculty of Forestry, UPM. 18 FORTROP II: Tropical Forestry Change in a Changing World

Sekhar, A.C. 1989. Rubberwood production and utilization. Rubber Research Institute of India, Kottayam. Wycherley, P.R. 1992. The Genus Hevea – Botanical Aspects, pp 50-56. In M.R. Sethuraj and N.M. Mathew, eds. Natural Rubber: Biology Cultivation and Technology. Developments in Crop Science 23, Elsevier, Amsterdam. van Buijtenen, J.P. 1969. Controlling Wood Properties by Forest Management TAPPI 52(2): 257-259.