A Problem Analysis
F. H. LANDON and G. G. K. SETTEN
Forest Department, Federation of Malayan
AT the FAO International Seminar for Forest Research Workers held at Dehra Dun, India, in 1955,1 all participants were requested to produce an analysis of the forestry problems of their countries. Forest services which are in the process of developing their research programs may wish to consider this digest of the Malayan problem analysis for possible adaptation to their own needs.
1 See Unasylva, Volume 10, Number 1, page 34. It is regretted that Mr F. H. Landon has died on service in Malaya since this paper was written.
The analysis briefly describes the problems which confront the Forest Department of the Federation of Malaya. According to government policy, the Department is responsible, under statute law, for the control of practically all forests and forest produce. The solution of problems involved in carrying out this responsibility requires careful, systematic research which is here outlined.
Part one of the problem analysis prepared for Malaya comprises basic data on the country, making up almost half the report, and grouped as follows:
1. general information: situation and composition, political format, people and population, economy and land status, geology, climate and recent history;
2. the forest estate covers: area, ownership, reservation, protection and productive forest, accessibility, surveys, forest composition, silvicultural characteristics, silvicultural system, management, exploitation and yield, revenue and expenditure, and legal status;
3. forest industries, local consumption and markets;
4. the Forest Department organization;
5. forest research organization: publications including Malayan forest records, The Malayan Forester, Malayan research pamphlets; the forest school.
In a country like Malaya, which still has 70 percent of its area under forest, it is reasonable to assume that the Government will continue to accept the policy that sufficient land should be retained under permanent productive forest to enable the estimated future demand for forest produce to be satisfied with an intensity of management that gives the highest returns per unit cost.
In planning to implement such a policy, it is necessary to make certain basic assumptions which must, however, be constantly reviewed in the light of experience or the results of experiments. The main assumptions made here are: that the population will continue to increase until it reaches about 28.5 million, or 217 per square kilometer, in 80 years time; that the consumption of saw timber per head will rise during the same period from the 1954 figure of 0.16 cubic meters round true measure to 0.28 cubic meters (the present consumption in the United Kingdom); and that the most economic method of forest management in Malaya is the present silvicultural system. Under this System, it is estimated that the present yield of 35 cubic meters per hectare obtained from virgin forest will be increased to 175 cubic meters, per hectare from properly managed regenerated forest in 70 years' time. Thus an annual coupe of 46,136 hectares will be needed to produce the required future annual yield of 8,017,000 cubic meters (i.e., 0.28 cubic meter each for 28.5 million people). For sustained yield on a 70-year rotation basis, this requires nearly 3,327,600 hectares or about 32,375 square kilometers (25 percent of the country), of productive forest reserve as compared with the 1954 total of 20,7120 square - kilometers. Since about 68,635 square kilometers of unalienated and unreserved State land remain below the 300-meter contour, it should be possible to reserve the additional 11,655 square kilometers and still leave ample land to supply the needs of agricultural and other expansion.
In order that the full production of 8,071,000 cubic meters per annum may be available at the earliest possible date, it will be necessary to increase the present forest reserve annual coupe, to be exploited and regenerated, to 46,136 hectares as soon as possible, and -at the same time to reduce output from unreserved State land to avoid overproduction in the early years. (This State land production will be required later.) This cannot be done without considerable increase in expenditure, not only on silvicultural operations (estimated to cost $74 per hectare at present rates) but. also on administration, research, traveling and the increased staff necessary to supervise work on this scale. A provisional estimate of the amount required annually is $3.4 million for silvicultural work and $6 million for other items, making a total $9.4 million compared with $4.8 million in 1954. By the time this total is reached, however, it is likely that annual revenue will have risen to at least $13 million from $10.8 million in 1954, which, it is estimated, will still leave a substantial surplus.
It will be a matter of policy for the Government to decide whether the goal of ultimate self-sufficiency in forest produce justifies the allotment of the additional 11,655 square kilometers to permanent productive forest and the investment of a higher proportion of the revenue into its regeneration. Having advised the Government on policy, it will be the task of the Forest Department - once the Government's decision is made - to make the best possible use of the forest areas and financial resources allotted to it. However, even if the Government does allocate the forest and finance necessary to permit a forest reserve annual coupe of 46,136 hectares, it must be emphasized that there will still be a gap between the saw-timber demand and the forest reserve production before the first of the new high-yielding regenerated crops becomes ready for harvesting about the year AD. 2025. This is demonstrated in the following Table:
TABLE 1. - ESTIMATED SCALE OF PRODUCTION AND CONSUMPTION 1956-2025
Consumption per head
Forest Reserve production at 35W per ha.
.......in cubic meters.......
1 Includes 20,235 ha. at 175 m3 per ha.
This Table does not take into account the requirements of Singapore, which will intensify the shortage. It is likely, however, that the timber production from unreserved State land forest, together with the more intensive utilization of existing virgin forest in both State land and forest reserve, will be able - as is the case now - to make good the deficit until the end of the century. The prospects for the last 25 years of the rotation period are, however, distinctly doubtful and will continue serious unless the present annual coupe is quickly increased to the required 46,136 hectares. It may well be that, during this period, the country will have to import timber.
The basic problems may therefore be phrased as two questions. How may the greatest possible amount of economic timber be produced in the shortest possible time under a sustained yield system, having regard to the Government's policy on land and finance? How may the total timber produced be used to the best possible advantage?
To answer the first problem, the following factors, among others, must he assessed:
1. Whether the present yield from virgin forest can be improved by silvicultural treatment prior to felling, by better exploitation techniques or by more intensive utilization.
2. Whether the new crops grown under the present silvicultural system can be economically improved in terms of composition, quantity (i.e., the volume of saw timber produced at any given time), and rate of growth - by means of silvicultural treatment, intermediate fellings, etc.
3. Whether, with the finance available, the yield of the natural forests can he supplemented by that of fast growing exotic plantations; and whether these plantations can be established on land which is regarded as useless for other purposes, e.g., on degraded soils not suitable for permanent agriculture.
4. Whether the effective yield of the forest can be improved by preventing the losses which occur prior to felling through natural causes, such as insect and fungal attack.
The assessment of these factors lies within several fields of research: silviculture, botany, ecology, soil science, mensuration, forest engineering, forest entomology and forest pathology, for example.
The answer to the second question requires the assessment of further factors:
1. Whether uses can be found for the timber grown in the forest which, for various reasons, is not at present utilized.
2. Whether, in its constructional and manufactured uses, the timber yield is utilized in the best and most economical fashion.
3. Whether the waste of timber which occurs after felling can be avoided by better sawmill practices and by preventing the losses caused by insects, fungal decay and such agencies as technical misuse.
In these cases, the assessment of the factors lies in the research fields of chemistry, entomology and timber research.
The research required to assess all the above factors, and the many corollary problems which they bring in their trail, is described in more detail in the sections below.
It is now possible to outline a program of projects which are required to answer the questions posed by the basic problems; it is arranged under the main heads of research. Past and current practice and future needs are also discussed.
Outline of program. The recognition of species is an essential for all silvicultural work. The two main requirements of the Botanical Branch are:
a) To identify specimens submitted to it. For this purpose the study of systematic botany and the development of a reference herbarium are necessary.
b) To publish descriptions and card keys by means of which species can be recognized in the field at all stages of their development. This requires intensive study of the leaf and bark characters of trees of all ages, and the standardization of the terminology used in describing these characters.
Past and current progress. A herbarium, started in 1918, has been built up to nearly 50,000 mounted specimens, besides numerous bark specimens. About 3,000 Malayan woody species are now known and it is unlikely that any more timber-yielding species remain to be discovered. There is good liaison with the Singapore Botanic Gardens, with Flora Malesiana and with the Borneon territories. An arboretum contains what is probably the best collection of Dipterocarp species in the world. Publications include an illustrated general book on Malayan Commercial Timber Trees (M.F.R. No. 3);2 an authoritative Manual of Malayan Dipterocarps with keys based on field characters (M.F.R. No. 16); a check list of the 500 to 600 tree species reaching timber size, giving botanical, vernacular and timber names, habitat, distribution and position in the canopy; and descriptions of all known timber species in six other important families (M.R.P. Nos. 1 to 16). Descriptions of other families of commercial importance are being prepared with a view to the publication of a Forester's Manual of Non-Dipterocarp Families. Numerous articles have been published in the Malayan Forester during the last 25 years, including a recent one introducing a standardized system of nomenclature for bole And bark characters, while a form of field collecting label has been produced, with Malay vernacular equivalents, carefully planned to elicit the maximum of information from collectors regarding field characters. The forest botanist has also done a great deal of ecological work, but this is discussed in the next section.
2 M.F.R. denotes the series entitled Malayan Forest Records; M.R.P. that of Malayan Research Pamphlets.
The authorized staff is one forest botanist, one assistant forest botanist, two research assistants and three plant collectors.
Future needs. The needs are:
1. the completion of the descriptions of the non-dipterocarp commercial families;
2. the preparation of a punch card key to timber species based on field characters;
3. the description of the less important tree families.
The authorized staff is sufficient provided that the posts are kept filled.
Ecology and soil science
Outline of program. Ecology and soil science are considered together because soil science is most unlikely to become a separate branch of forest research in Malaya. It will be a most important tool for the ecologist and silviculturist, but fundamental research on soils will continue to be more in the province of the Department of Agriculture. The work of the ecologist should be designed to assist the silviculturist in the choice of forest strata and of species. To do this he must:
a) study the composition and structure of natural forest and define vegetation types;
b) study succession after the original vegetation has been removed or modified;
c) study and define sites in terms of soil and other environmental factors which affect forest growth potential, so that they may be recognized at various stages of vegetational succession;
d) study the adaptability of species to various site conditions;
e) study which species and methods may best be used to accelerate the restoration of degraded land to productive forest.
Past and current progress. The Malayan climate is so favorable to forest growth that almost any soil may, given time, support a luxuriant vegetation, and the general structure of virgin forest throughout the country is remarkably similar. Within this framework, however, species are so numerous and variations so kaleidoscopic that chance differences between one square chain and the next, or one acre and the next, tend to obscure the fundamental site differences. A provisional classification of Malayan soils has been made by the soils chemist of the Rubber Research Institute and this classification has been tabulated and annotated by the silviculturist as an aid to their recognition in the forest. Nevertheless, progress in the recognition of sites and detailed vegetation types has been disappointing. The main vegetation types, however, have been described in Malayan Forest Record No. 16 and in recent articles by the forest botanist in the Malayan Nature Journal, while a number of studies of succession in secondary growth have been published in the Malayan Forester. The structure and composition of virgin forest, and its growth, in-growth and mortality, are being studied in 2-hectare sample plots.
In the absence of a full time ecologist, forest ecological work has hitherto been done by the forest botanist; but recently an ecologist has been appointed under the Commonwealth Development and Welfare Scheme with the special task of evolving methods of reclamation of degraded soils.
Future needs. Intensive work is required on the objectives outlined above, especially on the recognition of vegetation types and their correlation with soils. The forest botanist in the past could never spare sufficient time for this and a recent change of staff has made the position worse. The newly appointed ecologist is working full time on the restoration of degraded land. The need, therefore, is for a new permanent appointment of a forest ecologist.
Outline of program. Silviculture is very closely related to ecology on the one hand and to forest mensuration on the other. Working together, these three branches must provide the answer to the basic problem stated above, by determining whether silviculture may:
1. improve the yield from virgin forest by pre treatment;
2. improve the quality and yield of regenerated forests;
3. supplement the yield of natural forest by the economic establishment of fast growing exotic plantations.
Before much progress can be made, the silviculturist must become familiar with his treatment techniques and the habits of living plants.
The more important projects may therefore be out. lined as follows, (a) to (f) being basic and (g) to (j) applied:
a) summarizing past experience and existing knowledge of Malayan silviculture;
b) study of recruitment and survival of natural seedlings;
c) study of silvicultural characteristics and requirements of trees at all stages of development;
d) discovery of the best means of getting rid of unwanted growth;
e) improvement of nursery technique;
f) testing the suitability of local and exotic species for planting and the best methods of establishing plantations under different conditions;
g) establishing trial plantations, with costings, using species and methods which have shown promise in preliminary trials;
h) devising and testing techniques for the pretreatment of virgin stands with a view to increasing their outturn when they become due for felling;
i) testing the effects of various treatments on the composition - and stocking of young stands during the period of establishment;
j) testing the effects of various treatments On the increment And intermediate yields of established regenerated stands.
Past and current progress. Malaya has led the world in many aspects of tropical rain forest silviculture, and particularly in the conversion of virgin jungle to more or less even-aged stands of far greater potential value. Before the war, a technique had been developed and was being applied on an increasing commercial scale, whereby the useless or less valuable trees were removed by poison-girdling, by sale as firewood, or latterly by sale as timber, while a new crop was raised under the shelter of the remaining valuable trees until the latter were harvested as a " final felling ". Numerous articles in' the Malayan Forester and the first chapter of the Manual of Silviculture trace the development of the system. Economic considerations, including such factors as the increasing use of mechanized methods in extraction techniques and the replacement of the hand-sawyer by sawmills, have since compelled the adoption of the simpler system referred to above and described in detail in a paper entitled The Silviculture of Lowland Dipterocarp Forest submitted to the 1952 Commonwealth Forestry Conference. Hence projects (h), (i) and (j) are new problems, and little progress on them has been made to date. Progress on the other projects may he summarized as follows:
a) The silviculturist has spent much time during the last few years on the compilation of all available information regarding the inland low land forests. The results have been published as Parts 1, 3 and 4 of the Manual of Malayan Silviculture in Research Pamphlet No. 14, which deals with the History of Malayan Silviculture, Natural Regeneration and Artificial Regeneration.
b) Studies of the development of seedlings in scattered quadrats have been published in various volumes of the Malayan Forester. Milliacre (400 hectare) surveys of seedling regeneration are done in many cases before exploitation and results are being collected for compilation. There is only one permanent plot in inland forest for the study of mortality and recruitment in transects of milliacre (400 hectare) quadrats.
c) Much information is available in silvicultural files and the pages of the Malayan Forester on the characteristics of the more important species, and this is being assembled with a view to publication. Many other species which are now accepted, as timber have not yet been sufficiently studied.
d) Malaya led the way in the early 1930's in the large-scale use of sodium arsenite solution applied to frill girdles for the elimination of unwanted trees, and many tons of this poison have been used without casualties. A safer arboricide would, however, avoid much anxiety and the necessarily very stringent precautions. Experiments with other arboricides have been disappointing, but trials of the more promising 245-T are now being made on trees, climbers and other weeds.
e) Information about nursery techniques is included in the Manual of Silviculture referred to above, but has not been published separately.
f) The experimental plantations at the Research Institute now cover over 200 hectares and some are nearly 30 years old. Small-scale trials of exotics have been actively pursued during recent years, most indigenous species of value having been found difficult and expensive to establish on poor soils or in exposed conditions. The latest summary of trials with exotics was published in Volume XVI of the Malayan Forester.
g) One of the fastest growing exotics, Albizzia falcata, which after a test was reported to be suitable for paper pulp, was chosen in 1954 for an 8-hectare fire-protected plantation in Imperata grass. Further experiments in planting open or degraded areas have been entrusted to the ecologist appointed under the Commonwealth Development Scheme.
The silviculturist is assisted by a plantations officer and field staff in charge of the experimental plantations; and by a mobile research team of four, who can assist with experimental work in any part of the country and who also help with records and mensuration work.
Future needs. Continued work is necessary in all the basic projects (a) to (f), but more particularly in the study of the silvicultural characteristics of the lesser known species and the finding of a safe and economic arboricide. Projects (h) to (j) need planning from the start. No details are given here because the technique of measuring and comparing the effect of different treatments on such mixed rain forest stands has not yet been worked out. The problems will be discussed under the heading " mensuration " in the next section.
The silviculturist holds a key position in research but, in recent years, working-single handed, he has tended to be bogged down by routine work and the necessity for consolidating and making available past experience. With so much new work to be done, a fully-qualified assistant silviculturist is now a necessity.
Outline of program. As stated above, the forest mensuration program is closely allied to the silvicultural programme. The main mensuration projects are therefore as follows:
1. compilation and analysis of all existing sample plot data on the girth, basal area and volume increment of each species so far studied, or of various combinations of species, and the effects of various treatments on them;
2. construction of commercial volume tables based on two independent variables (basal area recorded in units of girth and clear bole height) for the main commercial species or, wherever possible, main groups of species;
3. design of a sampling scheme to investigate the composition and structure of existing regenerated forest; this will he followed by the execution of the scheme and the analysis of the results;
4. design of a permanent sample plot layout (in which the data to be recorded and the methods of analysis to be used will be specified) to investigate the effect of various silvicultural treatments on the increment3 and potential commercial yield of.
3 No Malayan tree species has annual rings which can be correlated with annual growth.
a) virgin forest prior to felling,
b) the young regeneration from the year 'n', when the old crop was felled, to the year 'n plus 10' the - establishment period,
c) the established regenerated crop between the year 'n plus 10' and maturity,
d) exotic plantations.
The Mensuration Branch will also assist the Silvicultural Branch in the execution of these designs and will analyze the data collected.
In all the above studies, very close liaison with the Silvicultural Branch will be maintained.
Past and current progress. The first sample plots were laid out in 1901, but the present series was not started until 1916. Since 1916, 381 sample plots have been laid out. Of this number, 34 contain no increment data and all records of 59 were destroyed during the 1939-45 war. The remainder contain the annual measurements (and other observations) of approximately 25,000 trees of 230 different species, although the majority of measurements have been made on the relatively few chief commercial species under varying conditions and treatments. These measurements have been made over varying lengths of time up to 39 years.
The first compilation of all inland forest sample plot data was made in 1928 and published as M.F.R. No. 9 The Growth of Malayan Forest Trees as shown by Sample Plot Records, 1915-1928. A second compilation had just been completed in 1941 when the invasion of Malaya took place. The whole of the second compilation and all the detailed work of the first were destroyed during the Occupation period. A fresh start on the compilation of all data collected since 1916 was therefore made in 1952, but subsequent progress has been slow.
Various volume tables were constructed prewar and published in the Malayan Forester. They were nearly all based on one independent variable (g.b.h.) only. Unfortunately, all the felled tree volume data on which they were based were destroyed during the war. The collection of fresh data was started again in 1947 and, by the end of 1954, the detailed measurements of some 7,000 felled trees had been obtained. The construction of the first new volume tables (for the two most common Shorea spp.) is now in progress.
The preliminary draft scheme for the sampling of the regenerated forests has already been considered by the Advisory Research Committee. A final scheme is now in course of preparation.
The draft rules for the layout and collection of data from silvicultural treatment plots have been formulated and given provisional. approval but some addenda are required. A series of investigations have been made to discover the best methods of analysing the data collected from permanent sample plots in mixed, unevenaged forest without growth rings, but the results achieved to date have been inconclusive.
The present authorized staff consists of one forest mensuration officer and one research assistant, but both these posts are now vacant.
Future needs. With regard to project 1, it is probable that this alone would occupy the undivided attention of one research officer and one assistant for a period of not less than two years. Project 2 depends for its progress on the rate of collection of the field data, but the first new volume tables could be constructed now if an officer were available for the work. Projects 3 and 4 also require the undivided attention of a qualified officer with computing staff.
If work on all four projects is to progress concurrently, the best solution would be the appointment of officers qualified in the use of statistics for specified projects only, each for a period sufficient to complete the project concerned, e.g., one officer for project 1 and, perhaps, project 2, and another for projects 3 and 4. A common staff of computing assistants could perhaps be used by both officers. Once projects 1 and 3 had been completed, it would be possible for one officer with two assistants to continue the work required.
Other research branches
Other research branches, though equally important, will not be discussed in detail in this study, their activities being similar the world over. The following paragraphs are explanatory of some local applications.
Entomology and pathology. The entomologist is working on the life history of pests, protection of plantations from insect attack, and the protection of timber at all stages from stump to ultimate use. In the past, special attention has been paid to the attacks of Ambrosia beetles, and a number of papers have been published on this subject.
There is no pathologist, protection against fungi being dealt with by the Timber Research Branch. There is one important problem under this head, however, that of " spongy heart " or " brittle heart " which causes serious degrade to the living trees of the two commonest light hardwood species, Shorea parvifolia and S. leprosula, especially the former in which the loss may amount to 30 to 50 percent. It is not known whether the degrade is due to fungal attack, to stresses in the living tree or to some other cause. It is possible that some factor such as soil deficiency may be a predisposing influence. At present the wood technologist is working on the problem.
Timber research. The objectives of this Branch are:
1. to make supplies of timber last longer and go further by proper seasoning and preservation methods, correct design and economy in dimensions used;
2. to find means of using timbers that are at present unsaleable.
It carries out tests of mechanical properties according to the standard international procedure for 2-inch square specimens and the results, published in the manuals of dipterocarp and non-dipterocarp timbers and in timber trade leaflets, have made possible the use of smaller dimensions and substitute timbers. Nevertheless, a lot remains to be done because the air-dry stocks of many important timbers that had been tested only in a green condition were either lost or destroyed during the war. A new development is the Composite, Wood Section, which will test the veneering and glueing properties of Malayan timbers.
Chemistry. A new Branch has started the study of the pulping properties for hardboard and paper manufacture of such sources of supply as mixed hardwoods, plantation species, rubber wood, bamboos, Imperata grass and rice straw. From the departmental point of view, the aim is to find uses for the large quantities of crown and branch wood of commercial species which are at present left to rot in the forest; and for the uneconomic tree species which do not attain 1 to 2 meters g.b.h. and are at present poisoned.
Research under the Conservator of Forests, Utilization. The departmental Branches under the control of the Conservator of Forests, Utilization, are shown in the Table. Broadly the research studies undertaken by these Branches may be listed as follows:
a) improvement of extraction techniques;
b) improvement of sawmilling procedure;
c) constructional uses of timber;
d) marketing research.
Under a), in conjunction with manufacturers' agents, trials are held of modern extraction equipment and demonstrations made to the logging industry. A recent trial was made of the Swiss-made Wyssen self-moving winch, which has aroused such interest in Europe. However, the manufacturers believe, on the strength of these trials, that modifications are necessary before it would be suitable for Malayan conditions.
Research under heads b) and c) is carried out in conjunction with the Timber Research Branch but on an applied scale. The forest engineer, under the Conservator of Forests, Utilization, has to approve all Malayan sawmill designs and often constructs the plans himself In conjunction with the Timber Research Branch, the correct uses of Malayan timbers in constructional design have been published in M.F.R. No. 13 (now under revision), and in diagrammatic leaflets. Termite-proofing techniques have been tested and published. A recent development was the full-size construction of a cheap housing unit using preserved secondary timbers and designed to sell at a basic cost of $ (Malayan) 2,300.
Under head d), the Timber Purchase Branch, in conjunction with the forest officer at Singapore, has been responsible for the Malayan grading rules for sawn timber. FAO has recommended that these rules should be adopted as a basis for the formulation of all such rules in Far Eastern and Pacific countries. This branch also runs timber depots for the purchase, sorting, grading, seasoning, preservation and sale of local timbers. At present, the problem of marketing secondary, less well-known timbers is having its attention. The solution of this problem may well be bound up with the construction of the cheap housing units mentioned above.
The Research Programme, of the Malayan Forest Research Institute, containing details of all the projects of the various branches, was published as Malayan Research Pamphlet No. 15 in 1954 and the Research Progress Report for 1954 as M.R.P. No. 15 A in 1955.
1. FOXWORTHY, F. W. Commercial Woods of the Malay Peninsula, 1921.
2. FOXWORTHY, F. W. Minor Forest Products of the Malay Peninsula, 1922.
3. FOXWORTHY, F. W. Commercial Timber Trees of the Malay Peninsula, 1927.
4. BLAIR, R. W. AND BYRON, F. E. Notes on Damar Penak, 1927.
5. WATSON, J. G. Malayan Plant Names, 1928.
6. WATSON, J. G. Mangrove Forests of the Malay Peninsula, 1928.
7. BUCKLEY, T. A. Mangrove Bark as a Tanning Material 1929.
8. FOXWORTY, F. W., WOOLLEY, H. W. and PENDLEBURY, H. M. Durability of Malayan Timbers with a Note on Termites, 1930.
9. EDWARDS, J. P. Growth of Malayan Forest Trees, 1930.
1 0. FOXWORTY, F. W. Dipterocarpaceae of the Malay Peninsula, 1932.
11. BUCKLEY, T. A. Damars of the Malay Peninsula, 1932.
12. DESH, H. E. Commercial Trees of the Malay Peninsula. The Genus Shorea, 1936.
13. DESH, H. E.. and THOMAS, A. V. Timber Utilization in Malaya, 1940.
14. DESH, H. E. Dipterocarp Timbers of the Malay Peninsula, 1940.
15. DESH, H. E. A Manual of Malayan Timbers, Part. I, 1940; Part. II, 1954.
16. SYMINGTON, C. F. A Forester's Manual of Dipterocarps, 1943.
17. WYATT-SMITH, J. S. A Pocket Check List of Malayan Timber Trees, 1952.
18. MENON P. K. B. A Card Key to Malayan Timbers, 1954. M. R. P. BARNARD, R. C. A Manual of Malayan Silviculture. Parts 1, 3 and 4, 1954.
BURKHILL, I. H. A Dictionary of the Economic Products of the Malay Peninsula, Government Printer, Singapore, 1930.
Among other journals or papers of reference are:
The Malayan Forester; Malayan Forest Department Timber Trade Leaflets; The Malayan Nature Journal and the Gardens Bulletin of the Singapore Botanic Gardens.