Rubber plantation performance in
the Northeast and East of Thailand
in relation to environmental conditions
Laura Rantala
A thesis submitted for an M.Sc degree in Forest Ecology
Department of Forest Ecology/
Viikki Tropical Resources Institute (VITRI)
University of Helsinki
Finland
2006
2
PREFACE
This M.Sc thesis was done under the framework of a project “Improving the productivity of
rubber smallholdings through rubber agroforestry systems in Indonesia and Thailand”. The
project is being financed by the Common Fund for Commodities (CFC). It is coordinated by
the World Agroforestry Centre (ICRAF), and research partners include the Indonesian Rubber
Research Institute, Kasetsart University (KU) and Prince of Songkhla University in Thailand,
and the University of Helsinki (UH). I received funding from the UH for travel expenses to
Thailand and for participation in a bilateral exchange programme between the universities of
Kasetsart and Helsinki.
My initial knowledge of rubber cultivation and the tropical environment was limited to say
the least. I am grateful to everyone involved in this work for the time they have generously
given for guiding me through the various stages of this work. Firstly I wish to express my
gratitude to my supervisor, Professor, Dr. Olavi Luukkanen (UH), Director of the Viikki
Tropical Resources Institute (VITRI), for making my participation in this project possible. I
am grateful for his supervision, valuable comments and interest in my work. During my field
work in Thailand, I received much academic as well as practical help from Associate
Professor, Dr. Suree Bhumibhamon and Dr. Damrong Pipatwattanakul (KU). Without their
support my work in Thailand would not have been possible. I am indebted to Dr. Vesa
Kaarakka (UH) for his help during various stages of my work and especially for thoughtful
comments on my manuscript.

2. LITERATURE REVIEW 11
2.1 Botany and distribution of Hevea brasiliensis 11
2.1.1 Distribution of Hevea brasiliensis in Thailand 12
2.2 Climatic requirements of the rubber tree 14
2.3 Soil requirements of the rubber tree 17
2.4 Rubber cultivation in Southeast Asia 18
2.4.1 General characteristics 18
2.4.2 Agroforestry practices 19
2.4.3 Environmental considerations 21
2.5 Uses of Hevea brasiliensis 22
3. MATERIAL AND METHODS FOR FIELD STUDY 23
3.1. Material 23
3.1.1 Field work and study areas 23
3.1.2 Plantation inventory 27
3.1.3 Interviews and field observations 28
3.1.4 Climatic conditions and soil types 28
3.2 Methods 31
3.2.1 Estimation of wood volume and biomass 31
3.2.2 Mann-Whitney's U-test 33
4. RESULTS 34
4.1 Plantation performance 34
4.1.1 Height and crown structure 34
4.1.2 Wood volume and biomass 37
4.2 Farming systems 44
4.2.1 General characteristics 44
4.2.2 Agroforestry practices and land use history 45
5. DISCUSSION 46
5.1 Variation in wood production potential between clones and study areas 46
5.2 Agroforestry practices in northeastern Thailand 49
5.3 Wood production potential in the Northeast and East compared to the South 50

RFD Royal Forest Department of Thailand
RIS Rubber Information System developed by the Department of Agriculture of Thailand
RRIM 600 Rubber Research Institute Malaysia's rubber clone number 600
RRIT Rubber Research Institute of Thailand
TMD Thai Meteorological Department
5
1. INTRODUCTION
1.1 Background of the study
The rubber tree, Hevea brasiliensis (Muell.) Arg., is a major crop for smallholders in Thailand
and an important commercial crop everywhere in Southeast Asia. It is grown for latex
production, while rubber wood is considered as a secondary product. Therefore rubber is
regarded as an agricultural crop. However, recent improvements in wood technology have led
to rubber tree becoming increasingly important as a source of wood products (Evans and
Turnbull 2004). Rubber wood has enjoyed an environmentally friendly reputation as a raw
material, because it is a by-product of latex production, and when grown in renewable
plantations, it can substitute timber from natural forests.
The natural range of Hevea, of the family Euphorbiaceae, covers the Amazon river basin and
parts of the nearby uplands. Within the genus, Hevea brasiliensis (also known as para rubber)
is one of the most widely distributed species. It grows in an area South of the Amazon river,
extending towards the west in Peru and the south to Bolivia and Brazil (Wycherley 1992).
The rubber tree has always been known for its latex, which was used by the ancient
civilizations of Central and South America. The commercial and large-scale exploitation of
the tree did not begin until in the last quarter of the 19
th
century. With the arrival of cars,
discovery of the pneumatic tyre and following increase in rubber prices, the produced amount
of plantation-originated rubber was soon larger than that of wild rubber. At the same time,
there were strong geo-political pressures to move the rubber production away from South
America (Jones and Allen 1992). While searching for a cash crop for its eastern colonies, the
British identified rubber as a potential crop for planting in Southeast Asia (Hong 1999).

world's largest producer of natural rubber (FAO 2006) and also the world leader in rubber
wood production and export (LDD 2005a).
The rubber plantation area in Thailand is much larger than the area of forest plantations in the
country. According to FAO (2005), the total area of rubber plantations in Thailand was
1 680 000 ha in 2005. According to the statistics of the Rubber Research Institute of Thailand
(RRIT 1996 cited in RFD 2000), the rubber plantation area was larger already in the year
2000, when it was recorded as 1 959 000 ha. In comparison, the area of forest plantations in
Thailand in the year 2000 was 355 000 hectares. The area of natural forest in the same year
was 16 486 500 hectares (RFD 2001).
1 In this study, areas of Thailand are referred to as South, Central, East, Northeast and North. A map of Thailand
and names of provinces in these areas is in Appendix 1.
7
Rubber has been referred to as a woody agricultural crop (FAO 2005) together with the oil
palm and coconut. In Thailand, the rubber plantation area is larger than the plantation area of
these two crops. In the year 2005, the plantation areas of rubber, oil palm and coconut were
1 680 000 ha, 315 000 ha and 343 000 ha, respectively (FAO 2006). The plantation areas of
both oil palm and rubber have been growing. Oil palm is cultivated in the South of Thailand,
which is also the traditional area for rubber cultivation. Competition for land area from other
crop species has been identified as one factor driving the establishment of rubber in new
areas.
In Thailand the smallholder rubber is intensively supported by the Royal Thai Government, in
forms of technology and production inputs such as seedlings, land preparation and fertilizer
(Joshi 2005). In recent years the Thai Government has been promoting rubber planting also in
new areas. In the year 2004, the goal was to extend the planted area, with a target of one
million rai (160 000 hectares) extension within two years from 2004 to 2006 (RRIT 2005).
The establishment of new rubber plantations has been promoted especially in the North and
Northeast of Thailand. The estimated extension of rubber cultivation area is 400 000 hectares
by the year 2010 (RRIT 2005).
In contrast to Malaysia, where rubber is mainly grown on large estates, in Thailand 90 % of
rubber is grown in family-owned smallholdings

It has been presented that unfavourable environmental conditions would more drastically
affect the latex yield than the timber production of rubber (Grist et al. 1998). In areas where
rubber cultivation is less favored by environmental conditions, improved farming systems
such as agroforestry could be an option for increasing the economical profitability as well as
environmental and social benefits of rubber cultivation.
Rubber plantations are usually established using vegetatively propagated and often improved
planting material. Clones perform differently in response to stress from external factors such
as drought (Rao and Vijayakumar 1992). The performance and wood production potential of
different clones in the non-traditional cultivation area (North and Northeast) in Thailand has
not yet been studied. The results from such studies would be useful in determining which
clones would be best suited for marginal planting areas.
Although latex is still the main product of rubber cultivation, wood selling can increase the
total productivity and enable reaching a maximum productivity of the rubber plantation
earlier. This is possible because wood selling can shorten the latex tapping period, after which
trees can be either felled or used for further tapping depending on the current prices of latex
and wood (Arshad et al. 1997; Clément-Demange 2004).
The wood production potential of rubber at a given site depends mainly on clone, planting
9
density and tapping practices. In the case of clones, their architecture, most importantly the
branching pattern, is a critical characteristic. Breeding of more suitable clones could lead to
better rubber wood productivity and increased income in the long term, but meanwhile clonal
recommendations can already be given (Clément-Demange 2004). The RRIT has already
grouped rubber clones into three classes according to their latex, timber and joint production
potential. Clonal recommendations for the non-traditional area in Thailand could be very
useful in order to determine which clones can be best adapted to a marginal cultivation
environment.
Plantation forestry and estate crops are controversial issues due to their reported negative
social and environmental impacts. Indeed, rubber plantation establishment has had some
direct negative environmental consequences in Thailand in the past. The logging ban of all
forests, which was declared in Thailand in 1989, was adopted following environmental

The general objective of this study was to investigate, using literature review and field data
collection, the wood production potential of two rubber clones in northeastern and eastern
Thailand in relation to environmental conditions and to study the characteristics of rubber
farming systems in northeastern Thailand.
The specific objectives of this study were:
1) To investigate the wood production potential (wood volume and clear bole volume as
related to plantation age) of rubber clones in relation to geographical area and climatic
conditions.
2) To compare the wood production potential of rubber clones in different geographical areas.
3) To preliminarily investigate the effects of site characteristics, especially the previous land-
use history, on the performance of rubber.
4) To preliminarily identify and study components of agroforestry systems used at rubber
plantations.
11
2. LITERATURE REVIEW
2.1 Botany and distribution of Hevea brasiliensis
Hevea brasiliensis is a tropical, deciduous tree, which grows 25-30 meters tall in its natural
distribution area. Most of the planted trees are smaller, because they have been bred for the
production of latex without taking much into account their wood production potential (Hong
1999). The bole of the rubber tree is usually straight but quickly tapered, and heavy branching
is common. The branching pattern is very variable, and the leading stem can be dominant or
soon divided into several heavy branches. The tree is easily damaged by strong winds
(Lemmens et al. 1995). Clonal variation in wind-resistance has been observed, depending on
types of branching (Cilas et al. 2004). Rubber tree matures at the age of seven to ten years,
after which latex tapping can be started. When aiming at economic latex production, the life
cycle of a rubber plantation is 30-35 years, after which replanting is necessary.
The current world-wide distribution of rubber plantations is presented in Figure 1. Apart from
Indonesia, Thailand and Malaysia, also India, Vietnam, China, Nigeria, Liberia, Sri Lanka
and Brazil, in descending order, have large areas (over 100 000 ha) of rubber plantations
(FAO 2006). In Table 1, the development in planted area and production of natural rubber in

Area Prod.
1990
Area Prod.
1995
Area Prod.
2000
Area Prod.
2005
Area Prod.
Indonesia 1 692 624 1 865 684 2 261 6 78 2 400 671 2 675 796
Thailand 1 411 548 1 400 1 013 1 496 1 378 1 524 1 560 1 680 1 798
Malaysia 1 535 957 1 645 800 1 475 738 1 300 714 1 400 839
2.1.1 Distribution of Hevea brasiliensis in Thailand
In 1996, the fourth survey on Thailand’s rubber plantation area was carried out by the RRIT
using Landsat satellite images. According to this survey, the total plantation area was 1 959
285 ha, of which 45 420 ha (2.3 %) were in the Northeast and North of Thailand. The eastern
provinces including Chachoengsao accounted for 12.3 % of the plantation area (RRIT 1996
cited in RFD 2000). According to Chantuma (2005), presently 5 % of the plantations are in
northeastern and 10 % in eastern Thailand. The Thai Government has targeted enlarging the
area of rubber plantation by 48 000 hectares in the North and 112 000 ha in the Northeast of
Thailand (Chantuma et al. 2005).
13
In terms of latex production, suitable rubber growing areas can be found also in the non-
traditional cultivation area in northeastern and northern Thailand. The Department of
Agriculture of Thailand has created a rubber information system (RIS), where climatic and
soil profile data are stored in a regional geographic information system (GIS) database. A
model for maximum latex production potential that was validated by using existing latex yield
data from the eastern provinces was used to evaluate and map the production potential in the
North and Northeast of Thailand.
Three rubber yield classes were determined. In class L1 the production potential is over 2500

latitude of the equator. The climate of this region is characterized by heavy rainfall and no
distinct dry season. According to Rao and Vijayakumar (1992), the optimal climatic
conditions for the genus Hevea are:
 A rainfall of 2000 mm or more, evenly distributed throughout the year with no severe
dry season and with 125-150 annual rainy days,
 A maximum temperature of about 29-34 °C, minimum of about 20 °C and a monthly
mean of 25-28 °C,
 High atmospheric humidity of about 80 % with moderate wind, and
 Bright sunshine for about 2000 hours in a year, at the rate of six hours a day in all
months.
15
In traditional rubber growing areas, the total rainfall ranges between 2000-4000 mm,
distributed over 140-220 days, without more than one to four dry months (Rao and
Vijayakumar 1992). Rubber can successfully be cultivated under these kinds of humid
lowland tropical conditions, roughly between 15°N and 10°S (Lemmens et al. 1995).
Cultivation of the tree has however expanded away from the equator to latitudes as far North
as 29°N in India, Myanmar and China, and down to 23°S in Brazil. In Thailand, rubber has
traditionally been cultivated on the Malay Peninsula from 6-12°N and in areas with an
average rainfall of around 2000 mm per year (Watson 1989). Cultivation in the East and
Northeast of Thailand (up to 18°N) has mainly started during the last two decades.
It is justified to make a distinction between the conditions that permit the survival of rubber
and those that assure best growth and yield (Compagnon 1987) and a cultivation which is
economically viable. A general lower limit of annual rainfall for the economically viable
cultivation of rubber can not be easily given, since environmental factors other than climate
also affect the survival of the tree (Compagnon 1987). A well-distributed annual rainfall of
1500 mm has sometimes been considered as a lower limit for commercial production
(Lemmens et al. 1995). However, the requirement depends on the distribution of rain
throughout the year, length of dry season and soil water retention capacity. In favorable soils,
rubber could tolerate a dry season of four to five months, during which less than 100 mm of
rain is received and within this period, two to three months with rainfall less than 50 mm

. Authors compared these results with figures from the traditional cultivation area
in Phuket and Surat Thani in southern Thailand, where plantations were 25 years old. Survival
was 78 % and 83 % and wood volume 256 and 300 m
3
ha
-1
, respectively (Chantuma et al.
2005). Wood volume was assessed based on tree girth. According to this study it seemed that
rubber wood productivity in the non-traditional area could be almost comparable to that in the
South of Thailand. However, it would be interesting to include several plantations in
consideration, also in the drought area of the Northeast, as well as to compare the
performance of different clones. It seems that the growth performance could be restricted in
the drought area, where trees encounter water stress especially during the hot and dry season.
The optimum day temperature for rubber is 26-28 °C. Night-time temperature drops to 10 °C
in Laos and Cambodia have not caused problems, but preferably the minimum temperature
should not drop below 14-15 °C (Compagnon 1987). During periods of low temperature,
slowing down of growth has been observed in China and in Northeast India. In China, where
rubber-growing areas lie between 18° and 24°N, the growth rate has been reported to slow
down drastically during the winter (Rao and Vijayakumar 1992). Cold damage, including the
death of shoots and a decreasing latex flow, has occurred when trees encounter hot and cold
conditions within one day and night temperature fall quickly to less than 5 °C and day
temperature rising to 15-20 °C (Watson 1989). Apart from latex flow and growth rate, cold
conditions have been reported to affect the survival during wintering and outbreak or
suppression of diseases (Jiang 1988). Different clones appear to vary greatly in their cold
resistance (Watson 1989).
17
Rubber trees shed their leaves annually, but the timing and intensity of leaf-shedding depends
on climatic condition and varies between clones (Lemmens et al. 1995). In eastern and
northeastern Thailand rubber trees shed their leaves in December, and start to grow new
leaves in January and February. Trees in the South drop their leaves approximately two

became an important crop for smallholders (Courtenay 1979). Still at present in Peninsular
Malaysia rubber is grown on smallholdings and estate plantations, the latter being
characteristic to Malaysia while the smallholder rubber is dominant in Thailand. The
plantations are for the most part 'monoculture', i.e. consisting of a single crop. In Indonesia
the practice is different- rubber is mainly cultivated in extensive and often complex
3
agroforestry systems, referred to as jungle rubber. In these systems rubber is the main crop
cultivated, but it is grown together with timber species, fruit trees, rattan or medicinal plants
(Wibawa 2005).
Incentives for improving the productivity of rubber cultivation can sometimes be limited. In
Indonesia, where the productivity of natural rubber per hectare is low, yield could be
improved by increasing the number of trees per hectare, and by planting better yielding rubber
varieties. However, expected land scarcity caused by outside land claims provides incentives
for securing future land rights by forest clearing and rubber planting, and not so much for
intensification of existing farming systems (Angelsen 1995).
Neither in Thailand is the land tenure secure in all cases. Private land ownership is recognized
step by step, from registration of land use to full ownership. The registration of land
occupancy is at present the only form of land security for millions of people, and although
3 The complex rubber agroforestry system includes a variety of plants, trees as well as treelets (banana, cocoa,
coffee), lianas and herbs which are all associated. The structure and functioning of these systems has been
reported to be close to that of a natural forest. A simple agroforestry system in turn consists of a smaller number
of plants, usually no more than five tree species and annual species (paddy or upland rice, maize, vegetables,
herbs) or treelets (Gouyon 2003).
19
these people are commonly regarded as owners of the land, a formal ownership is still missing
(Luukkanen 2001).
Government agencies supporting rubber planting in Thailand are the Rubber Research
Institute of Thailand (RRIT) and the Office of the Rubber Replanting Aid Fund (ORRAF).
The RRIT works under the Department of Agriculture (Ministry of Agriculture and
Cooperatives), and its responsibilities include rubber development plans, research, technology

sources of income (LDD 2005a).
When rubber trees are planted in widely used "standard" plantation pattern of 3 m x 7 m or
8 m, intercropping is generally possible only during the first years of rotation, before rubber
canopies close and do not allow the growth of light-demanding crops. A study by Rodrigo et
al. (2005) in Malaysia investigated the possibility to improve the productivity of rubber
agroforestry by altering planting patterns. Considering overall performance of long-term
intercropping, a double rubber row system with intercrops was identified as the best option
(Rodrigo et al. 2005). Wibawa et al. (2005) have also received encouraging results in long-
term intercropping using a rubber spacing of 6 m x 2 m x 14 m.
Another study by Rodrigo et al. (2004) demonstrates that apart from its overall economic
benefits, agroforestry can be beneficial to the growth of rubber trees. Intensive intercropping
of young rubber with banana may result in an increase in growth and yield of rubber trees,
and to a reduction in the length of the unproductive immature phase of rubber. Intercropping
had a positive effect on the growth of rubber throughout the six years of the study, with the
result that trees grown with intercrop were ready for tapping four months earlier than those
growing on their own (Rodrigo et al. 2004).
In Malaysia rubber has generally been planted as monocrop, but to increase productivity,
some farmers cultivate short term crops such as vegetables, corn, pineapple, groundnut and
banana between rubber rows during the first two and a half to three years of rotation. An
improved intercropping system has been developed in order to sustain the productivity of
intercropping over a longer period of time. In this system rubber is planted in one, double or
triple rows and the interhedges are planted with forest or fruit trees.
21
To assess the financial viability of rubber plantation with integrated forest trees, an
economical analysis was carried out comparing rubber agroforestry systems with integrated
timber trees to traditional monoculture plantations in terms of income in both smallholdings
and large estates. For the smallholdings, projected income from integrated timber species
seemed attractive. Hedge planting with rubber and teak (Tectona grandis) or sentang
(Azadirachta excelsa) was identified an option for consideration. Sentang or teak could
provide a bonus income at harvest while latex collection provides continuous supply of cash

under-estimated. Apparently due to its high leaf area index and the extra energy the tree
requires to produce latex, it acts as an effective carbon sink.
Intensive rubber growing areas can become vulnerable to soil nutrient loss and erosion that
result from ground preparation and clear-cutting. Growing rubber together with agricultural
crops could be the best way to decrease these environmental impacts. On steep slopes,
terracing has been recommended to prevent erosion (Royal Forest Department 2000). The
Land Development Department (LDD 2005a) has recommended planting of vetiver grass in
hilly areas for erosion control. While latex harvesting is practiced, fertilizer may be required
to replace nutrients lost (RFD 2000).
2.5 Uses of Hevea brasiliensis
The most important product of Hevea brasiliensis is the latex produced in the bark of the tree
and made into natural rubber. Rubber wood is generally considered as a by-product, and its
commercial value was almost non-existent until about 25 years ago. The wood was mainly
used as fuelwood and for charcoal making. The large supply and easy availability of rubber
wood were not attractive enough to the wood processing industries in the past. Lately, the
decreasing area and availability of natural forests for logging, increasing labour costs and
other factors have favoured the emergence of rubber wood as a raw material for mechanical
wood industry, especially for the manufacture of furniture and wood-based panel (Hong
1999).
Rubber wood can be a substitute for many species, including meranti (Shorea spp.), teak, oak
23
and pine (Balsiger et al. 2000). The timber is moderately durable and light creamy in colour,
which makes it attractive and popular among consumers. Rubber wood is also useful in
mechanical and chemical pulping processes to produce paper with fair quality. However,
some problems remain as special attention needs to be given to remove latex residues from
the pulp (Yussof 1999).
Thailand has a large rubber wood industry, and its products include furniture, particle board,
parquet board and construction boles (RFD 2000). The annual export value of Thailand's
furniture industry is more than 300 million US dollars (FAO 2005). Yet the rubber wood
industry in Thailand still faces some constraints and challenges within resource management

ample and relatively evenly distributed rainfall. On the other hand, the extreme Southeast
coast is very similar to the West coast of the peninsula (Pendleton 1962).
25
The driest regions of Thailand are found in the Northeast, on the Khorat platform, which
suffers from lack of water in the dry season. In the lower part of Khorat the average annual
rainfall is only 1050 mm. On the other hand, in the far Northeast, along the Mekong River,
over 2030 mm is received annually. Variation in the average amount of rainfall is therefore
notable in the Northeast. During the Northeast monsoon, winds can be relatively cold in
Khorat and thus also daily temperature variations are greater than those in the central valley
and in more maritime areas (Pendleton 1962).
Figure 3. Map of Thailand and study areas (district, province) (Map: Wikipedia, modified
www-document).