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Tài liệu Rubber plantation performance in the Northeast and East of Thailand in relation to environmental conditions docx

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.
In Thailand, I had the privilege to receive help from many people. I want to mention the staff
members of the Office of the Rubber Replanting Aid Fund in Bangkok, Nong Khai and
Buriram, who kindly assisted me in finding suitable sites for field study. I am grateful to Mr.
Arak Chantuma and Mrs. Pisamai Chantuma from Chachoengsao Rubber Research Centre for
providing me with the necessary facilities and assistance with the arrangements for my field
work. I want to thank Mr. and Mrs. Chorruk, Mr. and Mrs. Choochit and Mrs. Sompong
Puksa in Ban Kruen, Buriram, Mrs. Boonhouse Nanoy, Mr. Prasittiporn Sankarn and Mr. and
Mrs. Arlapol in Pak Khat, Nong Khai and Mrs. Pa Noom Thurtong in Lad Krating for
information, hospitality and for letting me conduct field inventories in their rubber
plantations. My field work would have not been possible without the help of Mr. Prin
Kalasee, Mr. Jakrapong Puakla, Ms. Waranuch Chansuri, Ms. Supanee Nakplang and Ms.
Pantaree Kongsat. I want to thank Mr. Chakrit Na Takuathung for helping me in finding
literature from Thailand once I had already returned to Finland. Finally I want to thank all
those who helped me and were very friendly to me making my short stay in KU and in
Thailand an unforgettable one.
I want to thank Professor, Dr. Jouko Laasasenaho and Timo Melkas for helping me with
calculating wood volume estimates for trees, and Riika Kilpikari for helping me with
statistics. Thanks are also due to Dr. Mohamed El Fadl for help in data search and comments
as well as to other VITRI staff and students for their comments. Last but not least I want to
thank my family and friends for their support.
Dublin, November 2006
Laura Rantala
This study was financed by the Common Fund for Commodities, an intergovernmental
financial institution established within the framework of the United Nations, headquartered in
Amsterdam, the Netherlands.
3
CONTENTS
1. INTRODUCTION 5
1.1 Background of the study 5
1.2 Scope and objective of the study 10


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
5.4 Critical assessment of the study 54
5.4.1 Aims achieved 54
5.4.2 Limitations of the study 55
6. CONCLUSIONS AND RECOMMENDATIONS 57
REFERENCES 59
4
LIST OF ABBREVIATIONS
BPM 2 4 Bank Pertanian Malaysia's rubber clone number 24
BB19 10-year old RRIM 600 stand in Buriram, 14°38'50 N, 103°12'72 E
BR10 16-year old RRIM 600 stand in Buriram, 14°38'56 N, 103°12'79 E
BR16 16-year old RRIM 600 stand in Buriram, 14°38'56 N, 103°12'79 E
BR03 3-year old RRIM 600 stand in Buriram, 14°38'65 N, 103°13'47 E
CB16 16-year old BPM 24 stand in Chachoengsao, 13°5' N, 101°5' E
CB08 8-year old BPM 24 stand in Chachoengsao, 13°5' N, 101°5' E
CR16 16-year old RRIM 600 stand in Chachoengsao, 13°5' N, 101°5' E
CR06 6-year old RRIM 600 stand in Chachoengsao, 13°5' N, 101°5' E
CR03 3-year old RRIM 600 stand in Chachoengsao, 13°59'41 N, 101°43'81 E
CRRC Chachoengsao Rubber Research Center (of the Rubber Research Institute of Thailand)
DBH Tree diameter at breast height (1.3 m)
DOA Department of Agriculture of Thailand
FAO Food and Agriculture Organization of the United Nations
GIS Geographic Information System
GPS Global Positioning System
LDD Land Development Department of Thailand
NB16 16-year old BPM 24 stand in Nong Khai, 18°37'11 N, 103°35'59 E
NB07 7-year old BPM 24 stand in Nong Khai, 18°36'09 N, 103°35'68 E
NR16 16-year old RRIM 600 stand in Nong Khai, 18°37'36 N, 103°35'60 E
NR08 8-year old RRIM 600 stand in Nong Khai, 18°36'09 N, 103°35'68 E
NR03 3-year old BPM 24 stand in Nong Khai, 18°37'07 N, 103°35'15 E
ORRA The Office of the Rubber Replanting Aid Fund
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).
Rubber was first introduced in Asia in 1876, when seeds were first shipped from the
Amazonas to the United Kingdom and further to Ceylon and planted there. In the following
year, rubber trees were planted in Singapore and Malaya (Hong 1999). Although rubber was
first an estate crop, local individual farmers soon adopted the crop and so they were drawn
into the world commercial economy (Courtenay 1979). Nowadays rubber is cultivated
worldwide in most parts of the lowland humid tropics, but the production is heavily
6
concentrated into Asia, where over 90 % of the world’s natural rubber is being produced.
Rubber seeds were first brought to Thailand from Malaya in 1900 and planted in Trang
province in southern Thailand (RFD 2000). Estate agriculture was for political reasons
discouraged in Thailand, unlike in Malaya, in the beginning of the 20
th
century. Rubber
growing became important as a smallholder crop, when local farmers responded to the
improved rubber prices in mid-1920s and planted rubber in southern Thailand (Courtenay
1979). Favourable climatic conditions, free land areas and easy railway access enabled the
adoption of rubber growing in the South (Pendleton 1962). Small areas were planted
elsewhere, mainly in Chantaburi province, where rubber seeds and seedlings from Malaya
were first taken in 1908. Later the cultivation extended to some other eastern provinces (RFD
2000).
Peninsular Malaysia has been the world's most important rubber cultivation area, and the
present wealth of this area was largely based on production of natural rubber (Collins et al.
1991). In the year 2005, Indonesia, Thailand and Malaysia produced 33 %, 23 % and 13 % of
the world’s natural rubber, respectively (FAO 2006). Lately, the rubber plantation area has
been decreasing in Malaysia, but in Thailand the trend has been reverse and plantations have
started to spread to new areas in the East and Northeast of Thailand
1
. This area has been
referred to as non-traditional for rubber cultivation (Chantuma et al. 2005). Today Thailand
has the second largest area of rubber plantations in the world following Indonesia, is the
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
2
less than eight hectares in size, the average
area of a plantation being only two hectares (Pratummintra 2005). Rubber yields per hectare
in Thailand are the highest of the three leading rubber-producing countries. This is due to
governmental support for smallholder rubber cultivation, and especially to the use of
improved planting material. Of the three leading rubber producers, the yield per hectare is
lowest in Indonesia, where rubber has traditionally been grown in “jungle rubber“
agroforestry systems. In these systems, the low yields have been reported to result from a low
level of maintenance and use of non-improved planting material (Wibawa et al. 2005).
Therefore, improving the productivity of rubber agroforestry has much potential especially in
2 In this study, the term smallholding is used to refer to family-owned small rubber plantations. The Department
of Agriculture (DOA) of Thailand has classified smallholdings, medium-sized holdings and estates as those
where rubber area is less than 8 hectares, 8-40 hectares and more than 40 hectares, respectively (Pratummintra
2005). According to Courtenay (1979), the smallholding is usually family-owned, managed by the family head
and worked by family labour. The plantation in turn is frequently owned by a company or a government
enterprise, and usually professionally managed (Courtenay 1979). In this study, the term plantation is, however,
used to refer to any organized planting regardless of size and management.
8
Indonesia. In Thailand’s case, a potential for increased production could lie in the
establishment of rubber in new areas. Therefore research on the performance of rubber in
these new areas is needed.
Rubber grows best in a climate similar to that in its area of origin in the Amazonas, where the
rainfall is heavy and there is no dry season (Rao and Vijayakumar 1992). In northeastern
Thailand, the annual rainfall is less than optimal for rubber and the dry season lasts for
approximately six months. In this climate, smaller wood volumes per hectare have been
reported in comparison with plantations in the traditional cultivation area (Chantuma et al.
2005). So far, comparative studies on the effect of climatic conditions to wood volume per
hectare and to individual volumes of trees in relation to plantation age have not been done. In
order to contribute to improving the productivity of rubber cultivation in Thailand, this kind
of information is needed.
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
degradation caused by logging and rubber plantation development on forest land (Collins et
al. 1991). After the ban, Thailand's timber has had to be taken from forest and rubber
plantations. This has been one of the main factors driving the increasing utilisation of rubber
wood for industrial purposes.
Rubber has been and still is an important commercial crop in Thailand and Southeast Asia. In
Thailand’s case, income from rubber cultivation is especially important for rubber
smallholders. According to RRIT (2005), there are over one million rubber smallholders in
the country. The demand for natural rubber has been predicted to rise from 8.4 million tonnes
in the year 2004 to 11.9 million tonnes in the year 2010 (Joshi 2005). As the demand for
rubber wood products remains high as well, it is important to ensure a sustainable and
sufficient future supply of rubber products while improving the productivity of farming
systems in order to contribute to ensuring good income for rubber smallholders in Thailand.
This report studied the performance and wood production potential of two rubber clones in
northeastern Thailand. The study was conducted under the framework of a Common Fund for
Commodities (CFC)- funded project “Improving the Productivity of Rubber Smallholdings
through Rubber Agroforestry Systems”. This project was coordinated by the World
Agroforestry Centre (ICRAF), and partners included the Indonesian Rubber Research
Institute, Prince of Songkhla University and Kasetsart University in Thailand, and the
University of Helsinki. This study was also a joint undertaking in the long series of academic
10
collaboration between the universities of Kasetsart and Helsinki.
1.2 Scope and objective of the study
The present study was carried out in Thailand in order to investigate the performance and
wood production potential of two rubber clones, namely RRIM 600 and BPM 24, in three
areas under different climatic conditions in northeastern and eastern Thailand. The wood
production potential was assessed through estimating the wood volume of individual trees and
plantations per hectare. As this study focused on the forestry-related uses of rubber, latex
yields were not measured. However when assessing the general profitability of rubber, the
latex yield component is currently the most significant factor in determining the viability of
rubber cultivation.
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
the three leading rubber-producing countries is compared.
12
Rubber plantation area, million ha and
percentage of world total in 2004
1400; 17 %
1740; 21 %
649; 8 %
154; 2 %
13; 0 %
1676; 20 %
2675; 32 %
Indonesia
Thailand
Malaysia
Rest of Asia
Africa
South America
Others
Figure 1. Rubber plantation area in the world in thousand hectares, and percentage of the total
planted area in the world in the year 2004. FAO 2006
Table 1. Rubber plantation area in 1000 hectares and the average production of natural
rubber in kilograms per hectare per year (kg
-1
ha
-1
a
-1
) between years 1985-2005 in Indonesia,
Malaysia and Thailand (FAO 2006).
Country 1985
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
kg per hectare per year (kg
-1
ha
-1
a
-1
). According to the RIS, this class was not found in the
North and Northeast, only in the South of Thailand. The second best class, L2, where the
production potential was estimated at 1500-2500 kg
-1
ha
-1
a
-1
was found in an area of about 320
000 hectares in the Northeast and 160 000 hectares in the North of Thailand. The third class,
L3, where production is lower than 1500 kg
-1
ha
-1
a
-1
and trees can not yet be exploited after
seven years from plantation establishment, was not regarded as a suitable area (Pratummintra
2005).
14
Figure 2. The area of rubber plantations in Thailand in the year 2000 according to RFD 2000,
and the share of the total area in different regions in 2005 (Chantuma 2005).
2.2 Climatic requirements of the rubber tree
The rubber tree is native to the evergreen tropical rainforests usually occurring within the 5°
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
(Compagnon 1987).
Plants encountering high temperature in the absence of rainfall are driven to higher rate of
transpiration which in turn leads to moisture stress. Effects of rainfall and temperature on the
photosynthetic rate (Sangsing 2004) and further the growth performance (Jiang 1988) and the
latex yield (Jiang 1988; Rao et al. 1990; Rao et al. 1996; Raj et al. 2005) of rubber trees have
been derived. In general, moisture stress has resulted in decreasing latex yields as well as
decreasing total production of dry matter. According to Grist et al. (1998), the growth and
latex yield of a tree are affected in different ways by soil moisture. Moisture stress has more
dramatic effects on the latex yield than on tree growth, as turgor pressure in latex vessels
inside the trunk of the tree is required to facilitate the latex flow.
Clonal differences in photosynthetic rates (Nataraja and Jacob 1998; Sangsing 2004) and
tolerance to moisture stress (Rao et al. 1990; Chandrashekar et al. 1998; Raj et al. 2005) have
16
been observed. Priyadarshan et al. (2005) studied the yield potential of several rubber clones
in marginal environments suffering from severe winds, low temperatures and high
evaporation in northeastern India. Clone RRIM 600 (Rubber Research Institute Malaysia,
clone number 600) appeared to be able to adapt well to various conditions, and produced
moderate yield in all marginal environments mentioned (Priyadarshan et al. 2005).
Chantuma et al. (2005) studied the wood production potential of clone RRIM 600 in the non-
traditional rubber cultivation area of northeastern Thailand. In Nong Khai province, the
survival percentage in a 15-year old plantation was 90 and the wood volume was 138 m
3
ha
-1
.
In Chachoengsao province, at a plantation aged 19, the survival was 79 % and wood volume
188 m
3
ha
-1
. 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
months later and start to produce new leaves in March and April (RFD 2000).
2.3 Soil requirements of the rubber tree
Rubber can grow on many soils, the best options being well drained (Lemmens et al. 1995)
clayey and deep clay soils (Growing multipurpose… 1994), but it can withstand physical
conditions ranging from stiff clay with poor drainage to well drained sandy loam. Soil water
retention capacity, depth and soil moisture are important factors determining the suitability of
a growing site. Ground covering plants can help improving the soil physical properties
(Krishnakumar and Potty 1992). An optimal soil pH value for rubber is at 5-6 (Lemmens et
al. 1995). The performance of the tree can be restricted where there is rocky surface, heavy
drainage or soil pH values above 6.5 or below 4 (Krishnakumar and Potty 1992).
In Thailand, rubber trees can be grown in many areas that are unsuitable for other commonly
cultivated cash crops. Rubber requires a modest level of soil nutrients when compared to
coffee, tea, coconut and oil palm. Some fertilizer is however advantageous and can be needed
to replace nutrients lost (RFD 2000).
The Land Development Department of Thailand (LDD) has carried out research in eastern
Thailand in order to identify soil types suitable for rubber planting in the East. According to
the study, soil properties essential for rubber are soil depth of at least one meter and moderate
fertility. Shallow soil, heavy stone layer at or above 50 centimeters from soil surface and low
level of fertility were regarded as unsuitable conditions for rubber cultivation. Suitable soil
series were found to cover 9 200 hectares in eastern Thailand (LDD 2005a).
18
2.4 Rubber cultivation in Southeast Asia
2.4.1 General characteristics
Because rubber has traditionally been classified as an agricultural crop, rubber plantations are
considered as agricultural land and not as forest plantation. However, the rubber tree is the
most widely planted tree species in Southeast Asia (FAO 2005). The characteristics of rubber
farming systems vary within Southeast Asia. In the beginning of the 20
th
century, estate
planting was encouraged in Malaya, while in Thailand and the Netherlands Indies rubber
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
transfer and control of natural rubber production, trade, exports and imports (RRIT 2005).
ORRAF is also attached to the Ministry of Agriculture and Cooperatives and it is a non-profit
enterprise carrying out governmental policies. ORRAF's objective is to work with rubber
farmers on rubber production, processing and marketing through providing improved varieties
of rubber seedlings, aiding in the establishment of both new plantations and replantings and
providing technology and guidance (Chaninthornsongkhla 2005).
In Thailand, rubber seedlings are usually produced by bud grafting on rootstock in nurseries.
Rubber seeds from high-yielding parents are first grown from four to eight months, until
stems reach a desired diameter at about 10 cm above ground, after which a grafting from a
desired clone is attached. Budwood clones are grown in specific bud-root gardens. The RRIT
has developed a certifying system in order to take care of the quality of planting material
produced at nurseries.
2.4.2 Agroforestry practices
Diversification of income through introducing food crops, timber trees or livestock in rubber
farming systems is a common practice in Southeast Asia. In Thailand, simple agroforestry
practices such as intercropping and integration of fruit trees have been adopted at
smallholdings in order to diversify sources of income. These practices have however not yet
been formally recommended nor well documented (Joshi 2005). The RRIT has carried out
research on various intercropping systems, and according to these studies, intercrops that
could successfully be grown with rubber in Thailand are banana, papaya, pineapple and
upland rice (RRIT 2005). Cherdchom et al. (2002) reported four main integrated rubber
farming systems in the South of Thailand emerging during the financial crisis in the late
20
1990's. The major systems included 1) Rubber intercrop farming, 2) Rubber-rice farming, 3)
Rubber-fruit tree farming, and 4) Rubber-livestock farming.
According to Joshi (2005), diversification of income sources through rubber agroforestry
systems could become more crucial in the non-traditional cultivation area, where rainfall is
low and other conditions less favorable for rubber, than in the South of Thailand. The LDD
has already recommended planting of food crops with rubber in eastern Thailand. Fruit trees
such as durian, mangosteen and rambutan were also recommended in order to diversify
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
before harvesting (Arshad et al. 1997).
In Indonesia, over 70 % of the total rubber area is jungle rubber agroforestry. A jungle rubber
cultivation system is usually established after slash-and-burn of secondary forest or old rubber
area. Complex rubber agroforests have been observed to preserve many functions of a natural
forest and therefore they could provide many environmental services: maintaining
biodiversity, retaining soil water captivation capacity and sequestering carbon from the
atmosphere (Joshi et al. 2002). However, complex agroforests are competing for land with
more intensive land use options. When incentives for retaining the traditional agroforestry
systems are not available, farmers often choose land use forms that provide fewer
environmental services. Efficient compensation such as a reward practice could help preserve
and promote complex agroforestry systems and the environmental services they provide
(Joshi et al. 2002).
The production of latex in jungle rubber agfororestry is very low- only about a third of that in
intensive monocultures. Improved rubber agroforestry systems have been succesfully
developed, studied and promoted in Indonesia in order to improve the productivity of rubber
cultivation. According to Xavier (2004), promising results on integrating plantation tree
species grown for timber in rubber agroforests have been observed in Indonesia.
2.4.3 Environmental considerations
Most of the original forest cover in Southeast Asia has been cleared for agriculture, including
rubber cultivation. In recent times the expansion of rubber growing into primary forest has
been most common in Indonesia, as a result of population growth, insecurity of land rights,
22
land scarcity and rising rubber prices (Angelsen 1995). Obviously, intensive rubber
cultivation can not be comparable to natural forest in terms of biodiversity, and rubber
cultivation should therefore not extend to areas covered with natural forest. In the case of
jungle rubber, as pointed out before, the complex agroforest could, however, perform many
ecological functions, and when comparing rubber cultivation with other land use alternatives,
the change from traditional shifting rice cultivation to smallholder rubber has been reported to
have various positive ecological effects in Indonesia (Angelsen 1995).
According to Balsiger et al. (2000), the role of rubber tree as a carbon sink has often been
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
as well as industries, product and market development. Although the resource base is large,
the quality of raw material is restricted. According to Anonymous (2000), the main problems
concerning resource management and utilisation were inefficiency of rubber wood raw
material management due to insufficient promotion and development of high-yielding
combined latex and timber clones, unfavourable infrastructure, and difficulties in logging
especially during rainy season, and restricting regulations for logging.
3. MATERIAL AND METHODS FOR FIELD STUDY
3.1. Material
3.1.1 Field work and study areas
Field work was carried out in northeastern and eastern Thailand between August and
November of 2005. The field work was conducted together and in collaboration with project
partners from CFC- funded project, “Improving the Productivity of Rubber Smallholdings
through Rubber Agroforestry Systems”. Project partners involved in field work were students
and staff from Kasetsart University, Bangkok.
Thailand is situated in the tropical zone between latitudes 6-20° North (N) and longitudes 98-
105° East (E). The climate is characterized by moderate rainfall and a hot dry summer. The
24
country has a monsoon climate: Northeast monsoon from December to February (the dry
season), hot weather and variable winds of March, April and May, Southwest monsoon from
May to October (the rainy season), and retreating monsoon period of October and November
(Pendleton 1962). Maximum day temperatures in Thailand change relatively little during the
year. In upper Thailand, the maximum temperature sometimes exceeds 40°C (Koteswaram
1974).
The amount and timing of rain is much more important to nature and agriculture in Thailand
than is temperature. Rainfall can be unpredictable, and the amount of rain can vary much from
place to place and from year to year. Most of Thailand receives the majority of rain during the
Southwest monsoon. Generally, the quantity of rainfall decreases with increasing distance
from the sea, but the amount of rainfall and the length of rainy season vary much depending
on area and altitude. The greatest quantities of rain (4200 mm annually on average) are
received on the West coast of the peninsula. The peninsula in general is characterized by
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).

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