UNIVERSITI PUTRA MALAYSIA
JUVENILITY IN RUBBERWOOD (HEVEA BRASILIENSIS) AND ITS RELATION WITH THE PHYSICAL AND MECHANICAL PROPERTIES
ROSLAN BIN MOHAMAD
FH 1998 5
JUVENILITY IN RUBBERWOOD (HEVEA BRASILIENSIS) AND ITS RELATION WITH THE PHYSICAL AND MECHANICAL PROPERTIES
By
ROSLAN BIN MOHAMAD
Thesis Submitted in Fulfilment of the Requirements for the Degree of Master of Science in the Faculty of Forestry Universiti Putra Malaysia
March 1998 ACKNOWLEDGEMENTS
First and foremost, I would like to express my utmost gratitute to Allah the Al
Mighty for His blessing in allowing this thesis to be completed on time.
Special thanks and recognition are given to the committee chairman, Associate
Prof. Dr. Mohd. Hamami Sahri for his guidance, suggestions and constructive criticisms throughout the preparation of this project. I am thankful for the guidance of my other committee members, namely Associate Prof. Mohd. Zin Jusoh and Dr.
Zaidon Ashaari for their help and commitments during the preparation of this research.
Sincere thanks to my former supervisor Dr. Mohamed Zakaria Hussin who is the first person to encourage me to pursue my study for the Master of Science. Sincere appreciation to the Dean of Faculty of Forestry for permission to use the facilities at the faculty. Special thanks to Dr. Faizah Abood Haris for editing the thesis.
Special thanks are also due to the Senior Research Officer of Golden Hope
Plantations Bhd, Dr. Mohd. Noor Abdul Ghani for supplying the research materials, research grants and great contribution towards successful completion of this project.
Many thanks are also due to his assistant Mr. Shahrom Jantan for the full cooperation given during preparation of rubberwood samples.
ii Sincere thanks to field assistants Mr. Razak and Mr. Rahmat for their contribution in preparation of the samples. Also, thanks to Mr. Omar Mohamad, Mr.
Saad, Mr. Harmaen, Mr. Hasidin and Mr. Abd. Jalal Aman fo r their full cooperation in the laboratory works.
A very special note of gratitude for my beloved wife, NorafizaAb. Rahman and my daughter, Fatin Faranisha for their encouragement, support and great contribution towards making this endeavour successful.
Special thanks to my beloved mother Jah bt. Tahir fo r her constant encouragement and support. Thanks are also due to my fa ther in-law, Ab. Rahman Hj.
Omar and mother in-law, Meriam bt. Mohamed and fa mily members Norizan, Arshad,
Aminuddin, Nurul Nisa, Noramalina and Nur Amira Syafiqah for their inspiration and encouragement.
iii TABLE OF CONTENTS
Page
ACKNOWLEDGEMENTS...... 11 LIST OF TABLES...... vii LIST OF FIGURES...... ix LIST OF PLATES...... Xl LIST OF ABBREVIATIONS...... xii AB STRACT...... xiii ABSTRAK...... xvi
CHAPTER
I INTRODUCTION...... 1 Justification...... 4 Objectives...... 5
II LITERATURE REVIEW...... " 6 Background ofRubberwood in Peninsular Malaysia...... 6 Anatomical Properties...... 7 Vessels...... 7 Fibres...... 8 Rays...... 11 Parenchyma...... 11 Physical Properties of Rubberwood...... 12 Specific Gravity...... 12 Shrinkage...... 13 Moisture Content...... 14 Colour...... 15
Mechanical Properties ofRub berwood...... 15 Woodworking Properties...... 16 Static Bending...... 18 Compression Parallel to Grain...... 20 Shear Parallel to Grain...... 20 Strength Properties of Rubberwood of Different Age Groups...... 21
iv Juvenile Wood...... 24
Properties of Juvenile Wood...... 27 Reaction Wood ...... 31 Shrinkage...... 32 Warping...... 33 Effect of Juvenile Wood in Various Products...... 34 Wood Based Panels...... 35 Pulp and Paper ...... 37 Plywood and Veneer ...... 37 Factors Influencing Strength Properties of Wood ...... 38 Specific Gravity...... 38 Moisture Content...... 40 Shrinkage and Swelling of Wood ...... 40 Other Inherent Factors...... 42
Strength Variation Among Species...... 42 Anatomical Features...... 42 Chemical Constituents...... 43 Position of Timber in a Tree ...... 44 Abnormal Growth of Wood ...... 44 Defects ...... 44 Tension Wood ...... 45
III MATERIALS AND METHODS ...... 46
Supply of Wood Samples...... 46 Sample Preparation...... 48 Anatomy and Wood Structure Study...... 50 Softening and Sectioning of Wood Block...... 50 Dehydration and Staining Process...... 53 Mounting Process...... 55 Maceration process...... 56 Evaluation of Physical and Mechanical Properties...... 57 Physical Properties...... 57 Mechanical Properties...... 59 Statistical Analysis...... 62
v IV RESULTS AND DISCUSSI ON...... 63 Anatomical Properties...... 63 Fibre Length...... 63 Fibre Diameter...... 71 Lumen Diameter...... 73 Cell Wall Thickness...... 75 Vessel Diameter...... 77 Vessel Frequency...... 80 Proportion of Fibres...... 83 . . Proportion of Rays...... 84 Physical Properties...... 88 Moisture Content...... 88 Specific Gravity...... 91 Shrinkage...... 94 Mechanical Properties...... 100 Modulus of Elasticity...... 100 Modulus of Rupture...... 104 Compression Parallel to Grain...... 106 Shear Parallel to Grain...... 110 Structure of Juvenile Wood and its Relation with Physical and Mechanical Properties...... 114 Fibre Length...... 114 Cell Wall Thickness...... 116 Specific Gravity...... 117 Chemical Constituents...... 119
V CONCLUSIONS AND RECOMMENDATIONS ...... 122 Conclusions...... 122 Recommendations...... 124
BIBLIOGRAPHy...... 125
APPENDIX A...... 133
APPENDIX B...... 138
APPENDIX C...... 141
144 VITA ......
vi LIST OF TABLES
Table Page
Percentage of tension wood in rubberwood at various ages and tree heights...... 3
2 Tissue proportion and fibre length of rubberwood...... 10
3 Physical properties of rubberwood...... 12
4 Average shrinkage of boards...... 14
5 Mechanical properties of rubberwood from different countries...... 16
6 Woodworking properties of rubberwood...... 17
7 Comparative strength properties of PB 260 clone rubberwood of different ages...... 22
8 Comparative strength properties of RRIM 600 clone rubberwood of different age group...... 23
9 Dimensions and number of samples for studies on anatomical, physical and mechanical properties...... 50
10 Mean anatomical characteristics for different clones and age groups...... 64
11 ANOVA results for anatomical properties of rubberwood...... 68
12 Duncan's Multiple Range Test mean values on the anatomical
properties of rubberwood ...... 69
13 Mean moisture contents and specific gravity for different clones and age groups...... 89
14 Mean shrinkage characteristics for different clones and age groups...... 96
15 ANOVA results for physical properties of rubberwood...... 98
vii 16 Duncan's Mltiple Range Test mean values on the physical
properties of rubberwood ...... 99
17 Mechanical properties for different clones and age groups ...... 101
18 ANOV A results for mechanical properties of rubberwood ...... 113
19 Duncan's MUltiple Range Test mean values on the mechanical
properties of rubberwood ...... 114
viii LIST OF FIGURES
Figure Page
Schematic representation of the gradual changes in properties from juvenile wood to mature wood in conifers...... 30
2 Bound water in the cell wall...... 41
3 Schematic diagram of the rubberwood sections...... 47
4 Schematic diagram for the preparation of test samples for mechanical properties...... 49
5 Sampling method for tissue proportion and fibre morphological studies...... 52
6 Schematic flow chart of double staining process using Safranin-O and Fast green...... 54
7 Arrangement of thin wood section on a glass slide...... 55
8 Mean fibre lengths at two radial positions for three clones of age 10 and 22 years...... 68
9 Mean fibre diameters at two radial positions for three clones of age 10 and 22 years...... 72
10 Mean lumen diameters at two radial positions for three clones of age 10 and 22 years...... 74
11 Mean cell wall thicknesses at two radial positions for three clones of age 10 and 22 years...... 76
12 Mean vessel diameters at two radial positions for three clones of age 10 and 22 years...... 78
13 Mean frequency of vessels at two radial positions for three clones of age 10 and 22 years...... 82
ix 14 Mean proportion of fibres at two radial positions for three clones of age 10and 22 years...... 83
15 Mean proportion of rays at two radial positions for three clones of age 10 and 22 years...... 86
16 Mean moisture contents at two radial positions for three clones of age 10 and 22 years...... 90
17 Mean specific gravity at two radial positions for three clones of age 10 and 22 years...... 93
18 Means of tangential shrinkage (%) at two radial positions for three clones of age 10 and 22 years...... 95
19 Means of radial shrinkage (%) at two radial positions for three clones of age 10 and 22 years ...... 97
20 Means of longitudinal shrinkage (%) at two radial positions for three clones of age 10 and 22 years ...... 99
21 Means of modulus of elasticity at two radial positions for three clones of age 10 and 22 years ...... 102
22 Means of modulus of rupture at two radial positions for three clones of age 10 and 22 years ...... 105
23 Means of compression parallel to grain at two radial positions for three clones of age 10 and 22 years ...... 109
24 Mean of shear parallel to grain at two radial positions for three clones of age 10 and 22 years...... 111
x LIST OF PLATES
Plate Page
1. Rubberwood fibres...... 66
2. A single rubberwood fibre ...... 66
3. Cross- section of rubberwood ...... 79
4. A group of vessels in cross- section ...... 79
. 5 . D·IS t rl 'b u t' Ion 0 f rays In rad' la I sect' Ion ...... , 87
6, Distribution of rays in tangential section...... , .. , ...... 87
7. Equipment layout showing rubberwood samples in static bending ...... 103
8. Equipment layout showing rubberwood samples in compression
parallel to grain test...... ,., ... , .,...... , ...... ,.,., . , .... " ...... , ...... ,. 108
9, Equipment layout showing rubberwood samples in shear
parallel to grain test.""" ,.,.,.,.,.,.,.,', ... ,. " .. , " " " ',., .," " ,.,, ., , ., , ., ., """""""" 112 ' ' '
xi LIST OF ABBREVIATIONS
BS British Standard
LSD least significant difference
Me moisture content
MDF medium density fibreboard
MTIB Malaysian Timber Industry Board
MOE modulus of elasticity
MOR modulus of rupture
MSR machine-stress rating
OD oven-dry
PB Prang Besar
RH relative humidity
RRIM Rubber Research Institute of Malaysia
SAS statistical analysis system
SG specific gravity
xii Abstract of thesis submitted to the Senate of Universiti Putra Malaysia in fulfilmentof the requirements fo r the degree of Master of Science
JUVENILITYIN RUBBERWOOD (HEVEA BRASILIENSIS) AND ITS RELATION WITH THE PHYSICAL AND MECHANICAL PROPERTIES
By
ROSLAN BIN MOHAMAD
March 1998
Chairman Dr. Mohd. Hamami bin Sahri
Faculty Forestry
Knowledge on anatomical, physical and mechanical properties of wood is necessary in assessing the potential utilisation of wood. The main objectives of this study are to determine the cellular composition and anatomical variations of juvenile rubberwood ( Hevea brasiliensis ) and their extent in the selected clones and age groups. Another objective is to determine the structure of juvenile wood in relation to physical and mechanical properties. Three different clones, PB 359, PB 366 and
RRIM 600 from two age groups, namely 10 and 22 years old were selected from
Golden Hope Plantation Bhd. Three trees were felled for each clone and age group.
Each tree was divided into three portions along the height namely, stump (SI)' trunk
xiii (S3) and branch (S5)' Outer and inner samples along the radial position were chosen for comparative studies on the anatomical, physical and mechanical properties. All samples for each test were prepared in accordance with the British Standard (BS 373:
1957) specifications.
Juvenile wood fromthe 10-yearold, Hevea trees of the clone PB 359 exhibited the highest values for fibrelength (1152.16�m) and initial moisture content (60.36%).
Clone PB 366 showed the highest values in fibre proportion (53.83%), MOR
2 2 (112.49N/mm ), MOE (9149.90N/mm ), and compression parallel to grain
(50.64N/rrun2) whereas RRIM 600 possessed the highest value in fibre diameter
(25.27�m), lumen diameter (12.28�m), shear parallel to grain (I 7.87 N/mm2) , tangential shrinkage (2.13%) and radial shrinkage (0.99%).
For mature wood of 22-year old, clone PB 359 showed the highest values in fibre length (1248.69�m), initial moisture content (65.96%), radial (0.69%) and longitudinal shrinkage (0.34%). Clone PB 366 possessed the highest value in fibre proportion (47.32%) and MOR (137.60N/mm\ whereas clone RRIM 600 showed the
3 highest value in fibre diameter (24.61�m), specific gravity (0.61g/cm ), tangential
2 shrinkage (1.49%), MOE (10422.48N/mm ), compression parallel to grain
(64.05N/mm2) and shear parallel to grain (20.S7N/mm2).
All clones fromthe 22-yearold age groups showed higher values for the fibre length, proportion of rays, moisture content, specific gravity, MOR, MOE, compression and shearparallel to grain when compared to similar clones from the 10- year old age group. For both age groups, the values for fibre length, fibre diameter,
xiv lumen diameter, cell wall thickness, vessel diameter, proportion of rays, specific gravity, MOR, MOE, compression and shear parallel to grain at the trunk (83) section were higher compared to the stump (81) and branch (85) sections.
The mechanical strength of the wood was found to be affected by fibre length, fibre diameter, cell wall thickness, proportion of fibres and specific gravity. Based on mechanical strength, 10-yearold juvenile rubberwood is suitable for the manufacturing of pulp and paper, solid wood products and medium-density fibreboard. Clone PB 366 is suitable fo r sawn timber due to the superior mechanical strength. Clone PB 359 can be processed to pulp and paper due to its lower lignin content and higher alpha cellulose and hemicellulose contents. Branch wood (85) possess similar anatomical, physical and mechanical properties to the trunk (83), and is also considered suitable for industrial utilisation. The stump (81), however possess lower mechanical strength properties and is not recommended fo r industrial utilisation.
xv Abstrak tesis ini dikemukakan kepada Senat Universiti Putra Malaysia untuk memenuhi keperluan ijazahMaster Sains.
KAYU GETAH MUDA ( HEVEA BRASILIENSIS) DAN PERKAITAN DENGAN CIRI-CIRI FIZIKAL DAN MEKANIKAL
By
ROSLAN BIN MOHAMAD
Mac 1998
Chairman Dr. Mohd. Hamamibin Sahri
Faculty Forestry
Pengetahuan tentang sifat-sifat anatomi, fizikal dan mekanikal kayu adalah penting bagi menentukan ciri-ciri istimewa serta kegunaan kayu itu sendiri. Tujuan utama kajian ini ialah untuk mengkaji komposisi tisu dan anatomi kayu getah muda
(Hevea brasiliensis) serta kehadiran dalam pelbagai jenis klon dan umur yang dipilih.
Ia juga bertujuan untuk mengetahui struktur kayu muda serta perkaitannya dengan sifat-sifat fizikal dan mekanikal kayu. Tiga klon yang berbeza iaitu PB 359, PB 366 dan RRIM 600 daripada dua kumpulan umur iaitu 10 dan 22 tahun telah dipilih dan diperoleh daripada Golden Hope Plantation Bhd. Tiga batang pokok dipilih daripada
xvi setiap klon dan umur yang sarna yang terdiri daripada tiga bahagian ketinggian iaitu tunggul (81), batang (83) dan dahan (85), Manakala bahagian luar dan dalam kayu pula dipilih sebagai uj ikaji perbandingan secara jejari untuk sifat-sifat anatomi, fizikal dan mekanikal kayu. 8emua sampel untuk setiap uj ikaji yang disediakan adalah mengikut spesifikasi British 8tandard (B8 373 : 1957 ).
Bagi kayu muda yang berumur 10 tahun, klan PB 359 mempunyai nilai tertinggi bagi panj ang gentian (1152.l6)lm) dan kandunganlembapan (60.36%). Klon
PB 366 menunjukkan nilai yang tertinggi untuk nisbah gentian (53.83%), MOR
(112.49N/mm2), MOE (9149.90N/mm2) dan mampatan selari ira (50.46N/mm2) manakala klan RRIM 600 pula menunj ukkan nilai yang tinggi untuk diameter gentian
(25.27)lm), diameter lumen (12.28)lm), ricihan selari dengan ira (17.87N/mm2), pengecutan arah tangen (2.13%) danjejari (0.99%).
Bagi kayu matang yang berumur 22 tahun pula, klon PB 359 menunjukkan nilai yang tertinggi bagi panjang gentian (1248.69)lm), kandungan lembapan (65.96%), pengecutan arah jejari (0.69%) dan memanjang (0.34%). Klan PB 366 mempunyai nilai yang tertinggi untuk nisbah gentian (47.32%) dan MOR (137.60N/mm2) manakala klan RRIM 600 pula menunjukkan nilai yang tertinggi untuk garis pusat gentian (24.61)lm), graviti spesifik (0.61g/cm\ pengecutan arah tangen (1.49%),
MOE (10422.48N/mm2), mampatan selari ira (64.05N/mm2) dan ricihan selari ira
(20.S7N/mm2).
8emua klan yang berumur 22 tahun menunjukkan nilai yang lebih tinggi bagi panjang gentian, nisbah ira, kandungan lembapan, graviti spesifik, MOR, MOE,
xvii mampatan selari ira dan ricihan yang selari ira jika dibandingkan dengan klon yang
sarna dari kumpulan umur 10 tahun. Bagi kedua-dua kumpulan umur, nilai pada
bahagian batang (S3) bagi panjang gentian, garis pusat gentian, garis pusat lumen,
ketebalan dinding gentian, garis pusat vessel, nisbah ira, graviti spesifik, MOR, MOE,
mampatan selari ira dan ricihan selari ira adalah tinggi jika dibandingkan dengan
tunggul (SI) dan dahan (S5)'
Kajian menunjukkan bahawa kekuatan mekanikal kayu adalah dipengaruhi oleh panj ang gentian, garis pusat gentian, ketebalan dinding sel, nisbah gentian dan graviti
spesifik. Berdasarkan kepada kekuatan mekanikal, kayu getah muda yang berurnur 10
tahun sesuai digunakan dalam pembuatan pulpa dan kertas, proses kayu pejal dan kayu
gentian ketumpatan sederhana. Klon PB 366 sesuai digunakan untuk pembuatan kayu
gergaji disebabkan oleh kekuatan mekanikal kayu tersebut. Klon PB 359 sesuai diproses untuk pembuatan pulpa dan kertas disebabkan kandungan lignin yang rendah
serta kandungan alfa-selulosa dan hemiselulosa yang tinggi. Kayu dahan (S5) masih boleh digunakan untuk tujuan industri di mana ciri-ciri anatomi, fizikaldan mekanikal hampir sarna dengan batang (S3) tetapi bagaimanapun tunggul (SI) tidak sesual
digunakan untuk tujuan industri sebab kekuatan mekanikal adalah rendah.
xviii CHAPTER I
INTRODUCTION
There is still a lack of information on the properties of juvenile wood and its utilisation fo r industrial purposes such as fo r manufacturing of pulp and paper, furnitureand wood composite boards in Malaysia.
However, some related studies have been conducted overseas. These include studies on juvenile wood in the manufacture of veneers from Douglas-fir (Kellogg and Kennedy, 1985), pulp and paper making (Jackson and Megraw, 1986), and the
production of wood composite boards fr om Douglas-fir (Lehnmanand Geimer, 1974 ) .
Generally, juvenile wood is known to be of lower quality than mature wood with respect to its low tensile strength, shorter fibre lengths and greater longitudinal shrinkage. Strength reduction and greater longitudinal shrinkage is due to greater average fibril angles in the cell wall (S2 layer). The specific gravity ofjuvenile wood is either higher or lower depending on the species, but is usually lower due to the formation of fe wer latewood cells and thinner cell wall layer. The chemical contents particularly lignin and hemicellulose are higher, thus resulting in a greater tendency of having spiral grains (Briggs and Smith, 1985). 2
In structural lumber, juvenile wood possesses lower strength values and tends to produce greater warpage as well as surface and cross checks. The strength values are usually around 15%-30% below normal although a reduction of 50% has been reported (Briggs and Smith, 1985). In veneer production, juvenile wood has a tendency to split and cause lathe checks which are rougher and deeper (Kelloggs and
Kennedy, 1985). In the production of pulp and paper (Megraw, 1985) reported that the juvenile wood of Douglas-fir was of a lower density, possessed a higher lignin content and produced less pulp. Megraw (1985) also noted that the pulping condition needed to be less severe due to the fragile cell wall as the shorter fibre lengths and greater fibril angle lowered its tear strength. Lehnman and Geimer (1974) reported a particleboard produced from Douglas-fir tops and branches including bark, possess lower strength and substantially poorer dimensional stability properties
Several studies have been conducted on the juvenile wood fr om different clones of rubberwood, such as studies on the proportion of tension wood (Vijendra Rao et aI.,
1983). Vijendra Rao et ai. (1983) noted that the proportion of tension wood in rubberwood fr om India varied for different samples taken from different heights of the same tree and also between different trees. The proportion of tension wood ranged fr om 15% to 65%. Ani and Lim (1992) studied the percentage of tension wood in two clones of rubberwood (PB 260 and RRIM 600) of different ages. They found that
RRIM 600 possessed a lower percentage of tension wood (30%) than PB 260 (40%). 3
For PB 260, the percentage of tension wood increased with height, whereas for RRIM
600, the percentage of tension wood decreased (Table 1).
Table 1
Percentage of tension wood in rubberwood at various ages and tree heights.
Age Clone ( year ) PB260 RRIM 600 B M T Mean B M T Mear
3 35 40 57 44 8 27 29 37 30 42 33 25 33 14 49 36 52 45 24 39 29 25 30
Note : B = Bottom M = Middle T = Top
Source : Ani Sulaiman and Lim (1992)
Due to the factors described, juvenile wood which is also called 'weak wood'
possesses great problems in wood processing. Many setbacks have been faced by
researchers when utilising juvenile wood for trusses, laminated beams and finger- jointed lumber. Similar problems are also faced by manufacturers of various panel
products such as plywood, conventional particleboards, oriented strand board (OSB),
medium density fibre board (MDF), weather boards and hard boards (Rice, 1973). It is
therefore essential to determine the properties of juvenile wood from various clones
andage groups ofrubberwood. The selected clones are 10 and20-yea r old ofPB 359, 4
PB 366 and RRIM 600. The main objectives of this study are to assess strength of juvenile rubberwood as well as to determine the structure of juvenile rubberwood and its relation to physical and mechanical properties.
Justification
Rubberwood is a versatile timber and is an important source of raw material fo r the production of many types of wood products (Lew, 1992; Chew, 1993). Recently, rubberwood emerged as the most popular wood used in the manufacture of furniture such as dining sets, occasional furniture, living room furniture, cabinets and even outdoor garden sets (Hong and Sim, 1985). The rubberwood supply from replanting schemes is decreasing fr om year to year. The availability of rubberwood in Peninsular
Malaysia in 1992 was about 9,360,698 m3 and decreased to about 8,909,272 m3 in 1994
(Anon, 1995). The tendency of using younger wood and timber of smaller diameter is becoming more common. The trend may become a normal practice as the supply of this timber becomes more scarce.
The utilisation ofjuvenile rubberwood fo r industrial purposes needs to be given
nore attention. Emphasis must be given on short rotation rubberwood especially fo r
ubberwood plantations of less than 15 years. This is because young rubberwood tends
o pose various problems in most manufacturing processes due to the greater
)ccurrence of spiral grain, the lower strength, lower density, shorter fibre length and 5 also greater longitudinal shrinkage. This study is thus important in assessing the suitability of juvenile rubberwood fo r utilisation in the manufacturing process as compared to mature rubberwood. Indirectly, it will provide additional preliminary information fo r the local and foreign manufacturers. The proper understanding and documentation of the properties and processing variability of juvenile rubberwoood fr om various age groups will definitely help towards the production high quality products as the matured rubberwood.
Objectives
The two main objectives of this study are as fo llows:
1. To determine the extent of juvenility in rubberwood in 10 and 22-year old trees
fromthree different clones.
2. To investigate the anatomical structure of juvenile rubberwood and their relation
with the physical and mechanical properties. CHAPTER II
LITERATURE REVIEW
Background of Rubberwood in Peninsular Malaysia
Peninsular Malaysia represents one of the world's largest producers of rubber.
There is about 1.82 million hectares of Hevea brasiliensis plantations (Anon, 1992).
Of the 1.82 million hectares found in Peninsular Malaysia, about 1.18 million hectares were reported to be small holdings. In 1990, about 0.94 million hectares of small holdings were managed by Rubber Industry Small Holders Development Authority
(RISDA) and about 0.24 million hectares were individually owned by small holders.
There were about 1,332 estate owners in Peninsular Malaysia (lsmariah and Norini,
1994).
The rubber trees generally reach their prime latex production in 25 years, after which they are no longer economical to produce latex, but their wood can be utilised for economic purposes (Anon, 1986). Within 25 years, rubber trees normally have clear boles of 3 to 10 m height depending on the clone. The diameter at breast height of rubber tree may reach 50 cm. Generally clone trees are shorter and smaller than trees raised from seeds (Hong and Lim, 1985).
6