Thesis_final_Rantala.pdf

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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 HelsinkiFinland

2006


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PREFACE

This M.Sc thesis was done under the framework of a project Improving the productivity ofrubber smallholdings through rubber agroforestry systems in Indonesia and Thailand. The

project is being financed by the Common Fund for Commodities (CFC). It is coordinated bythe 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 toThailand and for participation in a bilateral exchange programme between the universities ofKasetsart and Helsinki.

My initial knowledge of rubber cultivation and the tropical environment was limited to saythe least. I am grateful to everyone involved in this work for the time they have generouslygiven for guiding me through the various stages of this work. Firstly I wish to express mygratitude to my supervisor, Professor, Dr. Olavi Luukkanen (UH), Director of the ViikkiTropical Resources Institute (VITRI), for making my participation in this project possible. Iam grateful for his supervision, valuable comments and interest in my work. During my fieldwork in Thailand, I received much academic as well as practical help from Associate

Professor, Dr. Suree Bhumibhamon and Dr. Damrong Pipatwattanakul (KU). Without theirsupport my work in Thailand would not have been possible. I am indebted to Dr. VesaKaarakka (UH) for his help during various stages of my work and especially for thoughtfulcomments on my manuscript.

In Thailand, I had the privilege to receive help from many people. I want to mention the staffmembers of the Office of the Rubber Replanting Aid Fund in Bangkok, Nong Khai andBuriram, 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 fieldwork. 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. andMrs. Arlapol in Pak Khat, Nong Khai and Mrs. Pa Noom Thurtong in Lad Krating forinformation, 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. PrinKalasee, 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 findingliterature from Thailand once I had already returned to Finland. Finally I want to thank allthose who helped me and were very friendly to me making my short stay in KU and inThailand an unforgettable one.

I want to thank Professor, Dr. Jouko Laasasenaho and Timo Melkas for helping me withcalculating 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 commentsas well as to other VITRI staff and students for their comments. Last but not least I want tothank 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.


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CONTENTS

1. INTRODUCTION ...................................................................................................................... 5

1.1 Background of the study....................................................................................................... 5

1.2 Scope and objective of the study......................................................................................... 102. LITERATURE REVIEW.......................................................................................................... 11

2.1 Botany and distribution ofHevea brasiliensis ..................................................................... 11

2.1.1 Distribution ofHevea 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................................................................................................. 182.4.2 Agroforestry practices ................................................................................................. 19

2.4.3 Environmental considerations...................................................................................... 212.5 Uses ofHevea brasiliensis .................................................................................................. 22

3. MATERIAL AND METHODS FOR FIELD STUDY............................................................... 233.1. 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 ...................................................................................................... 344.1.1 Height and crown structure.......................................................................................... 34

4.1.2 Wood volume and biomass ......................................................................................... 374.2 Farming systems ................................................................................................................. 44

4.2.1 General characteristics................................................................................................. 444.2.2 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............................................................................................................. 545.4.2 Limitations of the study............................................................................................... 55

6. CONCLUSIONS AND RECOMMENDATIONS ..................................................................... 57

REFERENCES ............................................................................................................................. 59


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LIST OF ABBREVIATIONS

BPM 2 4 Bank Pertanian Malaysia's rubber clone number 24

BB19 10-year old RRIM 600 stand in Buriram, 1438'50 N, 10312'72 EBR10 16-year old RRIM 600 stand in Buriram, 1438'56 N, 10312'79 E

BR16 16-year old RRIM 600 stand in Buriram, 1438'56 N, 10312'79 E

BR03 3-year old RRIM 600 stand in Buriram, 1438'65 N, 10313'47 E

CB16 16-year old BPM 24 stand in Chachoengsao, 135' N, 1015' E

CB08 8-year old BPM 24 stand in Chachoengsao, 135' N, 1015' E

CR16 16-year old RRIM 600 stand in Chachoengsao, 135' N, 1015' E

CR06 6-year old RRIM 600 stand in Chachoengsao, 135' N, 1015' E

CR03 3-year old RRIM 600 stand in Chachoengsao, 1359'41 N, 10143'81 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, 1837'11 N, 10335'59 E

NB07 7-year old BPM 24 stand in Nong Khai, 1836'09 N, 10335'68 E

NR16 16-year old RRIM 600 stand in Nong Khai, 1837'36 N, 10335'60 E

NR08 8-year old RRIM 600 stand in Nong Khai, 1836'09 N, 10335'68 E

NR03 3-year old BPM 24 stand in Nong Khai, 1837'07 N, 10335'15 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


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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 ofHevea, 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


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concentrated into Asia, where over 90 % of the worlds 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 20th

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 worlds 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 Thailandand names of provinces in these areas is in Appendix 1.


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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 Departmentof Agriculture (DOA) of Thailand has classified smallholdings, medium-sized holdings and estates as thosewhere rubber area is less than 8 hectares, 8-40 hectares and more than 40 hectares, respectively (Pratummintra2005). 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.


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Indonesia. In Thailands 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 kindof 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; Clment-Demange 2004).

The wood production potential of rubber at a given site depends mainly on clone, planting


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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 (Clment-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 allforests, 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

Thailands 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


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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 ofrubber 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.


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2. LITERATURE REVIEW

2.1 Botany and distr ibuti on of Hevea brasi li ensis

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.


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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 %IndonesiaThailand

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 1985Area Prod.

1990Area Prod.

1995Area Prod.

2000Area Prod.

2005Area 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 ofHevea brasil iensisin Thailand

In 1996, the fourth survey on Thailands 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).


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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-1ha-1a-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 320000 hectares in the Northeast and 160 000 hectares in the North of Thailand. The third class,

L3, where production is lower than 1500 kg -1ha-1a-1 and trees can not yet be exploited after

seven years from plantation establishment, was not regarded as a suitable area (Pratummintra

2005).


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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 genusHevea 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.


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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 15N and 10S (Lemmens et al. 1995).

Cultivation of the tree has however expanded away from the equator to latitudes as far North

as 29N in India, Myanmar and China, and down to 23S in Brazil. In Thailand, rubber has

traditionally been cultivated on the Malay Peninsula from 6-12N 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 18N) 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 iseconomically 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; Chandrashekaret al. 1998; Raj et al. 2005) have


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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 m3ha-1.

In Chachoengsao province, at a plantation aged 19, the survival was 79 % and wood volume

188 m3ha

-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. Survivalwas 78 % and 83 % and wood volume 256 and 300 m3ha-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 24N, 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).


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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 Soi l r equirements 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 lowlevel 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).


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2.4 Rubber cul tivation 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 20th

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 complex3

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).


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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 varietiesof 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 agroforestrypractices 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


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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 or8 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.


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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 rubberarea. 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,


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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 H evea brasil iensis

The most important product ofHevea 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 rubberwood 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


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and pine (Balsigeret 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 problemsconcerning 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. Mater ial

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


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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 40C (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 dependingon 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).


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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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The first aim of this study was to investigate the performance of rubber in relation to climatic

conditions in the non-traditional cultivation area. Therefore it was necessary to conduct the

study in areas with different amounts of rainfall. The Northeast of Thailand has been

promoted for rubber plantation establishment, and, on the other hand, considerable variation

in the amount of rainfall exists within the northeastern region enabling the identification of

suitable study sites for comparison.

Ban Kruen district in the province of Buriram in the lower part of the Khorat plain

(approximately 14N, 103E), Pak Khat district in Nong Khai province by the Mekong River

in upper Khorat (approx. 18N, 103E) and Lad Krating village in Chachoengsao province in

the central valley at the border of Khorat region (approx. 13N, 101E) were selected as studysites. The locations of study areas are marked on the map (Figure 3). Chachoengsao formally

belongs to the East of Thailand, but since it is situated at the border of the Khorat plateau, in

this study the Chachoengsao area also is referred to as Northeast, in order to make a

distinction between the new cultivation area and the area of the South and East.

The other aim of this study was to compare the performance of two or more clones. To

overview the situation of rubber cultivation in northeastern Thailand, the Office of Rubber

Replanting Fund (ORRAF) was contacted in Bangkok. Local offices were also contacted in

Buriram and Nong Khai. With the help of ORRAF staff and local farmers, suitable study

areas were searched. It soon became evident that finding several clones for this study was

more difficult than previously expected. The main clone planted at smallholdings in the

Northeast of Thailand appeared to be RRIM 600 (Rubber Research Institute Malaysia, clone

number 600), BPM 24 (Bank Pertanian Malaysia, clone number 24) occupying less land. For

this reason, the study was limited to clones RRIM 600 and BPM 24. Both of these clones

have been classified as high-yielding latex clones by the RRIT (RFD 2000). According to

Sirianayu (2005), high-yielding timber clones or combined timber-latex clones have not yet

been planted in northeastern Thailand.

All plantations in Buriram and Nong Khai were smallholdings, and the size of individual

plantations ranged from 0.6 to 3.2 ha. The plantations in Chachoengsao, with the exception of

the youngest plantation which was a smallholding, belonged to Chachoengsao Rubber

Research Centre (CRRC), of the Rubber Research Institute of Thailand.


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The aim was to find plantations of both clones and of corresponding ages from all three study

areas, in order to make a comparison between clones and areas. In Buriram, young BPM 24

plantations could not be found. Neither in Nong Khai nor in Chachoengsao could newly

established BPM 24 plantations be found. The location of and other information on each

study site are presented in Table 2.

Table 2. Plantations included in this study. *) Approximate coordinates

No Province Location Clone Age Area,

ha

No of

trees/ha

Planting density

BR16 Buriram 1438'56 N

10312'79 E

RRIM600 16 1,3 360 3 m x 7 m

BR10 Buriram 1438'50 N10312'72 E

RRIM600 10 0,8 730 3 m x 6 m

BR03 Buriram 1438'65 N

10313'47 E

RRIM600 3 2,1 480 3 m x 7 m

BB19 Buriram 1438'51 N

10312'89 E

BPM24 19 1 390 3 m x 7 m

NR16 Nong Khai 1837'36 N

10335'60 E

RRIM600 16 2 400 3 m x 7 m


10335'68 E

RRIM600 8 0,6 530 3 m x 7 m


10335'15 E

RRIM600 3 0,8 545 3 m x 7 m

NB16 Nong Khai 1837'11 N

10335'59 E

BPM24 16 0,6 430 3 m x 7 m

NB07 Nong Khai 1836'09 N

10335'68 E

BPM24 7 1,3 310 3 m x 7 m

CR16 Chachoengsao 135' N *)

1015' E *)

RRIM600 16 0,8 420 2.5 m x 7 m, in blocks of

eight

CR06 Chachoengsao 135' N *)

1015' E *)

RRIM600 6 0,6 440 2.5 m x 7 m, in blocks of

eight

CR03 Chachoengsao 1359'41 N

10143'81 E

RRIM600 3 3,2 340 3 m x 7 m

CB16 Chachoengsao 135' N *)

1015' E *)

BPM24 15-16 4,8 200 2.5 m x 7 m, in blocks of

eight

CB08 Chachoengsao 135' N *)

1015' E *)

BPM24 8 6,4 180 2.5 m x 8 m, in blocks of

eight

3.1.2 Plantation inventory

At plantations trees were growing in lines, the planting pattern being 3 meters x 7 meters in

most places (planting pattern was measured using tape measure). This even distribution of

trees throughout the area enabled the plantation inventory to be conducted so that every 20 th

tree from horizontal lines was chosen as a sample tree. This systematic sampling resulted in

5 % of the total number of trees being measured. As the number of trees grows larger, small


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sample size leads to more reliable results than the same sample size at a smaller plantation

(Kangas and Pivinen 2000). For this reason at plantations larger than 20 rai (3.2 ha) every

50th tree was chosen as a sample tree, resulting in 2 % of the total number of trees being

measured. Altogether 302 trees were measured.

The following was measured from sample trees: diameter at breast height (DBH), girth at

breast height, tree height, height of crown, length of branch-free stem (also referred to as clear

bole) and the width of crown at two opposite points. Diameter and girth were measured at the

precision of 0.1 cm using tallmeter. Height attributes were measured at the precision of 0.5 m

using Suunto hypsometer. The length of branch-free stem was defined as the length of stem

from the ground before any branches started. Crown was defined to start where the foliage

started. Width of crown was measured from the ground using tape measure, at the precision of10 cm. The borders of each smallholding plantation were marked as way points using Garmin

eTrex Legend GPS navigator. The area of each plantation was defined using GPS. The

accuracy of Garmin eTrex Legend is about 15 m.

3.1.3 Interviews and field observations

The owners of each plantation were interviewed in Thai with the help of a translator. The

basic information of planted clone, area of plantation and age of the trees was obtained in this

way. In addition, information on plantation history and agroforestry practises was collected.

The list of questions asked is available in Appendix 2. The health of the trees, in case there

was any visible damage or illness, and signs of previous forest cover in plantation area were

visually observed in the field.

3.1.4 Climatic conditions and soil types

Meteorological data were obtained from the Thai Meteorological Department (TMD).

Rainfall data from the last 20 years included the amount of rainfall per month, amount of

rainy days per month and daily maximum. Temperature data included monthly mean,

minimum and maximum temperatures. Weather stations where the data were collected were

Nan Rong weather station, number 436401 in Buriram province, Chachoengsao weather

station, number 423001 in Chachoengsao province and Nong Khai weather station, number


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352201 in Nong Khai province. For temperatures, data from Chachoengsao station were not

available. Data from Chon Buri weather station, number 459201 in Chon Buri province were

used instead. Statistical data on the climatic conditions in study areas are presented in Table 3,

Figures 4 and 5 and in Appendix 3.

Table 3. Climatic conditions in study areas, mean values in parentheses. Data from the last

20 years (TMD 2005).

Study area

(district, province)

Rainfall, mm/year;

min-max (mean)

Annual rainy days;

min-max (mean)

Temperature,*) mean,

max, min

Dry period **)

Lad Krating,Chachoengsao

790-1400 (1180) 51-118 (88) 28.6, 39.9, 13 6 months

Ban Kruen, Buriram 840-1500 (1150) 85-142 (113) 27, 41.8, 8.5 6 months

Pak Khat, Nong Khai 930-2250 (1570) 106-156 (128) 26.4, 42.8, 4.9 6 months

*) Lad Krating statistics from Chon Buri province, approximately 100 km to the South from

Lad Krating.

**) Number of months when rainfall is less than 100 mm, 20-year average.

Figure 4. Mean annual rainfall in mm in study areas between the years 1984-2004

(TMD 2005).

1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004

600800

1000

1200

1400

1600

1800

2000

2200

2400

Annual rainfall in study areas

Buriram

Nong Khai

Chachoengsao

Year

Rainfall,mm


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Figure 5. Number of annual rainy days in study areas (TMD 2005).

Information on soil types was collected using soil maps, literature and the soil information

CD-ROM of Land Development Department of Thailand (LDD). Some of these documents

were translated from Thai into English. In Buriram and Nong Khai, local soil doctor

volunteers trained by LDD were interviewed for information on soil types, soil condition and

problems related to soil. The LDD has trained soil doctors since 1995, and presently there are

55 000 soil doctors in villages in Thailand (LDD 2005b). They are in charge of coordinating

land development between the LDD and farmers in villages, transferring new technology to

their neighbours and participating in activities of the LDD (LDD 2005b).

Table 4. Soil conditions in study areas (Soilview 2.0, Soil map of Buriram province, Soil map

of Chachoengsao province, Characterization of established... 2003, all published by the LDD;Pintha 2005).

Study area Soil type Soil series PH values Draining Character Natural

vegetation

Land use

Problems

Lad Krating,Chachoengsao

Sandy loam Acid to stronglyacid, pH 4.5-5.5

Welldrained

Deep soil DryDipterocarp

forest

Sandy soil,water

deficiency, low

natural fertility,

erosion

Ban Kruen,

Buriram

Laterite

clay, laterite

Strongly acid to

neutral

pH 4.5-7

Well

drained

Shallow soil Dry open

Dipterocarp

forest

Shallow soil,

low natural

fertility, erosion

Pak Khat,

Nong Khai

Sandy

loam,

loamy sand,

loam

Mixture of

Khorat and

Phonpisai

soil series

Very strongly

acid to strongly

acid

pH


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3.2 Methods

3.2.1 Estimation of wood volume and biomass

Bole volume (also referred to as wood volume, excludes bark, branches and leaves) and total

dry biomass were calculated for each tree using volume and biomass models developed for

Hevea brasiliensis by Risnen (1997) in Mexico. These models were created based on

material consisting of 19 trees for bole volume model and 9 trees for biomass model.

Bole volume Vb, dm3

= 0.065789 * d2.179986

* h0.488780

, excluding bark, branches and leaves.

Residual error 13.5 % (Risnen 1997) (Equation 1)

Total biomass B, kilograms = 0.066218 * d2.131143

* hc0.612696

Residual error 6.5 % (Risnen 1997) (Equation 2)

In these models, d= DBH in centimetres, h = height in meters, and hc = height of crown in

meters.

Another model, developed in Thailand by the RFD, was also used to estimate wood volumes.

For creating RFD's volume model, 931 trees from the South and East of Thailand were

measured.

Volume V, m3 = 0.0000461697 * x 2.0816, including bark and branches.

(RFD cited in Urapeepatanapong 1989) (Equation 3)

In this model, x is girth at breast height (1.3 m) in centimeters.

This model gives the total volume of a tree, which can be further divided into sawn timber

(usable volume), fuelwood and wood residues, and pole (Urapeepatanapong 1989).

Mean square error for the inventory results (sample y) was calculated using the following

formula:

Mean Square Error, Se = var y (Kangas and Pivinen 2000) (Equation 4)


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Mean variance, var= ( 1- (n/N) * (Sy2/n) )

where n = number of samples, N= total number of trees, Sy = distribution

(Kangas and Pivinen 2000) (Equation 5)

Mean square errors for results on wood volume and biomass using these volume models

varied from 1.8 % to 17.8 %. Mean square errors are presented in Figure 6.

Figure 6. Mean square error percentage for wood volume and biomass estimates for eachplantation. Plantation abbreviations: BB19- Buriram, BPM 24, 19 years; BR16- Buriram, RRIM 600, 16 years; BR10-Buriram, RRIM 600, 10 years; NB16- Nong Khai, BPM24, 16 years; NR16- Nong Khai, RRIM 600, 16 years; NB07- NongKhai, BPM 24, 7 years, NR08- Nong Khai, RRIM 600, 8 years; CB16- Chachoengsao, BPM 24, 16 years; CR16-Chachoengsao, RRIM 600, 16 years; CB08- Chachoengsao, BPM 24, years; CR06- Chachoengsao, RRIM 600, 6 years

In plantations NB16 and CB08, the distribution values within population grew large, because

a few trees included as sample trees were larger than average.

In addition, the volume of clear bole was calculated. This is the volume of the economically

valuable lower part of trunk, before branching begins. For calculating this volume, trunk

diameter at the point where first branches start was needed. These diameters were not

measured in the field, and to attain values for these diameters, a taper curve was used. A taper

curve for rubber trees growing in Mexico was created by Risnen (1997) and it was found to

be relatively similar to that of silver birch (Betula pendula), created by Laasasenaho (1982).

BB19 1ha

BR161.3 ha

BR100.8 ha

NB160.6 ha

NR16 2ha

NR080.6 ha

NB071.3 ha

CR160.8 ha

CB164.8 ha

CR060.6 ha

CB086.4 ha

0

2

4

6

8

10

12

14

16

18

Mean square error for estimated woodvolume and biomass

Volume, m3/ha(Risnen)

Volume, m3/ha (RFD)

Biomass, kg/ha(Risnen)

Plantation

Meansquareerror%


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Therefore the taper curve of silver birch was used in this study to get estimates for clear bole

volume of rubber trunks. A polynomial form model for silver birch was developed by

Laasasenaho (1982). Using this model, a taper curve could be calculated when tree height and

DBH were known. From this taper curve it was possible to get estimates for diameter at

branching point and further calculate the volume of the clear bole. In order to get closer

estimates of volume, a correction equation was used.

The number of trees per hectare for each plantation and further the wood volume per hectare

was calculated using total number of trees and the area of plantation. However, some

problems were encountered. Firstly, the exact area of all plantations could not be verified due

to technical problems. Trees were not distributed evenly and planting densities varied: most

common planting pattern was 3 m x 7 m, leading to approximately 480 planted trees perhectare. However, higher densities such as 3 m x 6 m and 2.5 m x 7 m were used at some

plantations, and at one plantation the planting density was 3 m x 8 m. In CRRC, trees were

planted in blocks, and at one plantation the total number of trees per hectare was as low as

180. Highest number of trees per hectare was 730. To minimize the effects of estimated

number of trees per hectare and planting pattern to the results, the wood volume per hectare

was calculated as though standard planting density of 3 m x 7 m had been used at all

plantations and all trees had survived. This creates over-estimation of wood volume, but at the

same time it facilitates the comparison of two clones and different areas.

3.2.2 Mann-Whitney's U-test

In order to investigate variation between populations, i.e. 1) the variation in wood volume

between clones RRIM 600 and BPM 24 in each study site and 2) the variation in wood

volume within clones RRIM 600 and BPM 24 between study sites, a non-parametric Mann-Whitney's U-test was chosen, because the sample size in some plantations was small (less

than 20 trees) and therefore a test based on the application of normal distribution risks giving

inaccurate results (Ranta et al. 1989). Mann-Whitney's U-test was carried out in SPSS 14.0

for Windows software.


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4. RESULTS

4.1 Plantation perf ormance

4.1.1 Height and crown structure

On average, RRIM 600 clones aged 16 were 17.4 meters tall while BPM 24 clones aged 16-

19 were 15.3 meters tall. Yet BPM 24 always had taller clear boles than RRIM 600. On

average, BPM 24 had a clear bole measuring 4.9 meters while RRIM 600 had 3.8 meters of

clear bole. In plantations aged 16 or more, BPM 24 clones had a clear bole measuring 4.5

meters while the clear bole of RRIM 600 trees was approximately 3.6 meters tall.

Clone RRIM 600 grew taller than clone BPM 24 in all three areas. There were no differences

in average height of RRIM 600 trees between Buriram (144' N, 1032' E, average height 16.7

m) and Chachoengsao (135'N, 1015'E, average height 16.5 m). In Nong Khai (184'N,

1033'E) average height was taller, 19.1 meters. In all three areas the height of RRIM 600

trees varied to a similar extent but within different minimum and maximum figures. In

ascending order, height of 16 years old RRIM 600 trees varied between 10 and 19.5 meters in

Chachoengsao, 12.3-21.5 m in Buriram and 16-25 m in Nong Khai.

BPM 24 clones aged 16 or older grew much taller in Nong Khai (average height being 18 m)

compared to Buriram (13.9 m) and Chachoengsao (14.9 m). In Buriram, height of 19-year old

trees varied between 10-19 meters, in Chachoengsao (trees aged 16) between 10-19.5 m and

in Nong Khai (trees aged 16) between 12-22 m.


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Figure 7. Average height and proportion of clear bole (in brown) in meters in plantations,

excluding young (three-year old) plantations. Plantation abbreviations: BB19- Buriram, BPM 24, 19 years;BR16- Buriram, RRIM 600, 16 years; BR10- Buriram, RRIM 600, 10 years; NB16- Nong Khai, BPM24, 16 years; NR16-Nong Khai, RRIM 600, 16 years; NB07- Nong Khai, BPM 24, 7 years, NR08- Nong Khai, RRIM 600, 8 years; CB16-Chachoengsao, BPM 24, 16 years; CR16- Chachoengsao, RRIM 600, 16 years; CB08- Chachoengsao, BPM 24, years;CR06- Chachoengsao, RRIM 600, 6 years.

Average height of RRIM 600 trees as related to plantation age.

Plantation age, years

Figure 8. Development of mean height in meters as related to plantation age in three RRIM

600 plantations in Nong Khai and Chachoengsao and in two plantations in Buriram.

As seen in Figure 8, the growth development of clone RRIM 600 seemed to be faster in Nong

Khai than in Chachoengsao and Buriram. Trees also seemed to reach a taller maximum height

in Nong Khai than in the other two study areas. By the end of a rotation (approx. 30 years),

according to this estimate, an average height of rubber trees in Nong Khai could be about 25

BB19 BR16 BR10 // NR16 NB16 NB07 NR08 // CR16 CB16 CR06 CB08

0

5

10

15

20

25

Average height and proportion of clear bole

Plantation

Height,m


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meters while in Buriram and Chachoengsao the average height would be about 20 meters.

Early growth of clone RRIM 600 was compared between the three study areas. In Nong Khai

the average girth was 10.5 centimetres and average height 4 meters, in Buriram 10.9 cm and

5.7 m and in Chachoengsao 16.2 cm and 6.4 m, respectively. Mann-Whitney's U-test was

carried out in order to investigate the differences between these areas.

Table 5. Average girth and average height in three-year old plantations in Buriram, NongKhai and Chachoengsao. Means sharing the same letter are not significantly different at

P > 0.05 (Mann-Whitney's U-test). Standard error of the average (mean) is indicated by thenumber in parentheses.

Study site Girth, cm Height, m

Buriram 10.90a

(0.68)

5.71

(0.32)

Nongkhai 10.52a(0.44)

3.95(1.30)

Chachoengsao 16.20(0.02)

6.44(0.54)

The average widths of crowns are presented in Figure 9. There seem to be no marked

differences in crown structure between the two clones or the three areas. Only in Buriram,

clone RRIM 600 appeared to develop a narrow crown. This may be affected by the fact that

the plantation BR16 was suffering from bark disease.


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Figure 9. Average width of crowns (in centimeters) in study areas. Plantation abbreviations: BB19-Buriram, BPM 24, 19 years; BR16- Buriram, RRIM 600, 16 years; BR10- Buriram, RRIM 600, 10 years; NB16- Nong Khai,BPM24, 16 years; NR16- Nong Khai, RRIM 600, 16 years; NB07- Nong Khai, BPM 24, 7 years, NR08- Nong Khai, RRIM600, 8 years; CB16- Chachoengsao, BPM 24, 16 years; CR16- Chachoengsao, RRIM 600, 16 years; CB08- Chachoengsao,

BPM 24, years; CR06- Chachoengsao, RRIM 600, 6 years.

4.1.2 Wood volume and biomass

General character istics

Average wood volume estimates received using Risnen's (1997) volume equation and

RFD's equation (RFD 1988 cited in Urapeepatanapong 1989) are shown in Figure 10. Thestandard deviations for volume in different plantations are available in Appendix 4.

Risnen's volume equation gave an estimate of bole volume excluding bark and branches,

while RFD's equation gave a wood volume estimate which includes the volume of bark and

branches. Risnen's model, which used height as a function, produced 23-41 % smaller

results than RFD's model, depending on study area. RFD's model has been developed in the

South and East of Thailand, and does not include tree height as a factor. Inclusion of height

reduced the volume estimates for all plantations. The difference appeared especially

significant in Buriram. According to RFD's volume equation, which was based solely on the

girth of trees, plantation volume calculated for standard planting density was the highest, 128

m3ha-1, in one plantation (BR16) in Buriram. Using Risnen's equation, plantation NR16 in

Nong Khai had the highest volume, 99 m3ha-1.

BB19 BR16 BR10 // NR16 NB16 NB07 NR08 // CR16 CB16 CR06 CB08

0

100

200

300

400

500

600

700

Average width of crown

Plantation

Averagew

idth

ofcrown,

cm


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Figure 10. Individual volumes of trees in dm3

using Risnen's volume model, excluding bark

and branches, and RFD's volume model, including bark and branches.Plantation abbreviations:

BB19- Buriram, BPM 24, 19 years; BR16- Buriram, RRIM 600, 16 years; BR10- Buriram, RRIM 600, 10 years; NB16-Nong Khai, BPM24, 16 years; NR16- Nong Khai, RRIM 600, 16 years; NB07- Nong Khai, BPM 24, 7 years, NR08- NongKhai, RRIM 600, 8 years; CB16- Chachoengsao, BPM 24, 16 years; CR16- Chachoengsao, RRIM 600, 16 years; CB08-

Chachoengsao, BPM 24, years; CR06- Chachoengsao, RRIM 600, 6 years.

In further studies, the volume estimates received using Risnen's volume equation were used.

Generally volume equations based on height and DBH or more functions give more accurate

results than those based on only one function (DBH) and are less vulnerable to variation

caused by changes in environmental conditions. This can be seen in Figure 10, where RFD's

equation resulted to higher volume estimates than Risnen's equation especially in Buriram,

where apparently due to environmental conditions, trees were shorter than in Nong Khai.

The wood volume estimates for clone BPM 24 were smaller than those for clone RRIM 600

in all three regions. The difference between the two clones seemed to be most remarkable in

Nong Khai. The difference was apparent also in Buriram, where a plantation of BPM 24 aged

19 years had smaller wood volume per hectare than a plantation of RRIM 600 which was

three years younger. Wood volume in the BPM 24 plantation was 75 m3ha-1, while the

volume in RRIM 600 plantation was 88 m3ha

-1. In Nong Khai, plantations of the same age

(16) of BPM 24 and RRIM 600 had wood volumes of 65 and 98 m3ha-1 , respectively.

However, in younger plantations in Nong Khai, (NB07 and NR08), the differences were not

so marked, 45 and 50 m3ha-1, respectively. Taking into account the age of the plantations,

seven years for BPM 24 and eight years for RRIM 600, the difference appeared to be non-

BB19 BR16 BR10 // NB16 NR16 NB07 NR08 // CB16 CR16 CB08 CR06

0

50

100

150

200

250

300

Average wood volume of one tree

Volume, dm3/tree(Risnen)

Volume, dm3/tree (RFD)

Plantation

Woodvolume,dm

3


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existent. In Chachoengsao province, plantations CB16 and CR16 did not differ significantly

in terms of volume per hectare (69 and 77 m3ha

-1, respectively). Also, there seemed to be no

marked difference between the performance of these clones in younger plantations (CB08: 53

m3ha-1 and CR06: 33 m3ha-1). There seemed to be no marked differences in wood volumes of

clone BPM 24 between the three regions. RRIM 600 grew largest in Nong Khai, followed by

Buriram and Chachoengsao.

For Figure 11, wood volume per hectare was calculated using Risnen's volume equation and

a standard planting pattern (3 m x 7 m) for all plantations in order to eliminate the effect of

planting pattern and number of survived trees. In addition, volume per hectare was calculated

using the actual number of trees observed in plantations.

Figure 11. Wood volume estimates in m3ha-1 calculated for standard planting density of 3 m x

7 m and as related to actual number of trees per hectare. Plantation abbreviations: BB19- Buriram, BPM

24, 19 years; BR16- Buriram, RRIM 600, 16 years; BR10- Buriram, RRIM 600, 10 years; NB16- Nong Khai, BPM24, 16years; NR16- Nong Khai, RRIM 600, 16 years; NB07- Nong Khai, BPM 24, 7 years, NR08- Nong Khai, RRIM 600, 8 years;CB16- Chachoengsao, BPM 24, 16 years; CR16- Chachoengsao, RRIM 600, 16 years; CB08- Chachoengsao, BPM 24,years; CR06- Chachoengsao, RRIM 600, 6 years.

From Figure 11 it can be seen that the effect of planting pattern and number of trees per

hectare on the results for wood volume per hectare could be decisive. In plantation BR10, the

planting pattern was 3 m x 6 m. In Chachoengsao, in plantations CR16, CB16 and CR06, the

pattern was 2.5 m x 7 m, in CB08 2.5 m x 8 m, and in all plantations trees grew in blocks of


0

20

40

60

80

100

120

Average wood volume per hectare

Volume, m3/ha, instandard planting pattern

Volume, m3/ha asrelated to observednumber of trees/ha

Plantation

Woo

dvolu

me,

m3/ha


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eight in horizontal lines. In order to make wood volume estimates more comparable between

plantations and less dependent on planting pattern and survival percentage, wood volume

estimates calculated for standard planting density of 3 m x 7 m were used in further analysis.

Clear bole volume, i.e. the volume of the branch-free lower part of stem, is the proportion of

trunk that can be used as sawn timber. Branches and tops are usually used for fuelwood and in

charcoal-making. To compare the performance of rubber trees in a marginal area in terms of

wood production potential, it was essential to pay attention mainly to the productivity of

industrially utilisable wood. Estimates received for clear bole volume in m3ha-1 are shown in

Figure 12.

Figure 12. Average clear bole volume (volume of branch-free lower part of trunk) in m 3ha-1 at

plantations, calculated using taper curve of silver birch (Betula pendula). Plantation abbreviations:BB19- Buriram, BPM 24, 19 years; BR16- Buriram, RRIM 600, 16 years; BR10- Buriram, RRIM 600, 10 years; NB16-Nong Khai, BPM24, 16 years; NR16- Nong Khai, RRIM 600, 16 years; NB07- Nong Khai, BPM 24, 7 years, NR08- Nong

Khai, RRIM 600, 8 years; CB16- Chachoengsao, BPM 24, 16 years; CR16- Chachoengsao, RRIM 600, 16 years; CB08-Chachoengsao, BPM 24, years; CR06- Chachoengsao, RRIM 600, 6 years.

The volume of clear bole was the highest (63 m3ha-1) in plantation NR16 (RRIM 600) in

Nong Khai. The second largest volume was observed in plantations in Buriram, clone BPM

24 (53 m3ha-1) followed by clone RRIM 600 (50 m3ha-1). In Chachoengsao the wood volume

was smaller, but in the same order, clone BPM 24 (44 m3ha

-1) followed by clone RRIM 600

(42 m3ha-1). In Buriram and Chachoengsao, clone RRIM 600 produced a larger wood volume

per hectare, but BPM 24 produced a larger volume of clear bole. The same development was

visible in Chachoengsao and in Nong Khai in younger plantations. The average length of

clear bole was taller in clone BPM 24 than that in clone RRIM 600 in all areas.


10

20

30

40

50

60

70

Average volume of clear bole

Plantation

Volumeofclearbole,m3/ha


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Recovery rates

Recovery rates (the shares of usable wood volume of total bole volume) were calculated for

each plantation. In this study, recovery rate means only the usable wood's percentage of bole

volum

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