Jean Collardet
JEAN COLLARDET is the former Director of the Centre technique du bois in Paris.
More research and better marketing are needed; but techniques and machinery are available
The range of tropical woods is extremely vast. It comprises thousands of species, the properties of which differ greatly: density varies from 0.1 or less for balsa to 1.35 for lignum vitae; mechanical strength varies in the same way; some species are to a high degree liable to deterioration, while others are practically rot-proof. To identify and describe accurately all these woods it is necessary to determine scientifically their anatomy, their chemical, physical and mechanical properties and any technological characteristics, giving priority to the most common species.
A number of forest research institutes or timber technology laboratories have, in their respective countries or territories, carried out such research and published information or accumulated valuable data. The methods of testing used in these various laboratories are unfortunately not the same, so that the results are not always comparable. It is therefore desirable in future to use only the standardized methods of the international Standards Organization (I.S.O.) or, at least, the methods of testing applied should be described in detail and factors of correlation established between the main methods of testing, so as to facilitate the interpretation of results.
The compilation of available data has already been undertaken by various research workers (9, 10); and the Centre technique forestier tropical (CTFT), which is responsible for centralizing and making use of the results obtained in about ten institutes or laboratories, has published a work reproducing the 1068 technical data sheets corresponding to 732 different species for which data have been collected (11).
Recently a substantial portion of the FAO Forestry Department's marketing work was directed towards assessing the role of commercial and lesser-used wood species for the three major tropical timber producing areas. The basis for these studies is information on the occurrence, denomination, production and trade of wood species, and also includes an evaluation of basic use properties, wood uses and values, and relative commercial importance.
Following the recommendation made by the FAO Committee on Forest Development in the Tropics, during its second session, that particular attention be given to the role that research could play regarding the use of tropical species and extending their markets, IUFRO has established "Study Group P5.01" on the properties and utilization of tropical woods.
This study group has initiated work to identify and gather together, by means of a questionnaire, all sources of information, determine the characteristics and properties of work of research institutes and laboratories while avoiding so far as possible duplication of effort.
In fact, at present, a wide range of information and of quite precise data on the tropical species currently exploited or most abundant is available. This relates particularly to their form and dimensions, their anatomical structure, and the characteristics for macro-or micro-identification of their woods, their density, their dimensional stability, their resistance to the main mechanical stresses (compression parallel to grain, static and impact bending strength, hardness and elasticity). Other information of some practical importance such as durability, ease or conditions of drying, sawing and machining, slicing and peeling or finishing are often lacking or of only subjective quality. Tests have often been empirical, gathered by too few users and not supported by measurements. By way of contrast, it has been established that botanical and anatomical identification has not always been exact for species that have so far hardly been marketed, if at all, and which are considered as secondary because of their poor economic impact. Appraisement of these species is often contradictory, whether seeking to explain their neglect or to promote them and their properties have often been only superficially studied.
It is necessary to break out of this vicious circle since it is precisely the neglected species that should have been studied in depth, in order to ascertain their characteristics and use potentialities accurately. Detailed information has been accumulated on the well-known species simply because of their frequency and qualities and from the knowledge about them acquired through long experience. Many tropical countries are today aware of this need, and now give priority to research and trials on species only slightly or incompletely known. This has happened in Ivory Coast, Ghana, Nigeria, Cameroon, Gabon, and Brazil. It is also true in several southeast Asian countries, such as Indonesia, the Philippines, Thailand, Burma and Malaysia, which because their forest flora is to some extent common, have concentrated their attention since the recent symposium held in the Philippines (12) on the coordination of their research and the dissemination of results among themselves.
In view of the large number of secondary species to be described, the laboratories would not be able to carry out a complete programme on each of them, since tests entail considerable work, funds and time. Rather it is necessary to proceed step by step dealing in the first instance only with species of sufficiently frequent occurrence - to be of some economic interest. Preliminary tests should be limited to the determination of essential characteristics in order to be able to select species which seem to offer interesting properties for certain uses. These species would then merit being put under some more scientific scrutiny based on a significant number of samples from different provenances. Above all they should undergo practical tests of seasoning machining, and application for various purposes.
It is fortunate, in this connection that in a general way the characteristics and properties of woods of tropical moist forest are generally homogeneous in structure and vary little within one botanical species, from one individual to another. This applies through various ecological conditions or provenances and thus limits the number of samples necessary for complete descriptions of each species, and does away with the need for repetition as with woods of seasonal zones where very many tests are needed to obtain statistically valid data. Samples tested should nevertheless be seriously identified, selected and described. This has not always been done in the past and has led at times to ill-considered conclusions.
The tropical species are evidently expected to satisfy all the needs of producing countries, and also requirements of developed countries for whom for decades they have supplemented the supplies of native woods or those imported from other temperate countries. This is, qualitatively and quantitatively, because of their appearance or other particular characteristics, their ample dimensions, and their high industrial yield.
Naturally, save possibly for fuel-wood, the properties and technological characteristics of each species will dictate the choice for any particular use. For well-known species which have been marketed for a long time, such attribution is the result of empirical experience or long tradition. Marketing today of species of which little or nothing is known would clearly be greatly eased by acquisition of precise knowledge of their characteristics or idiosyncrasies, as well as the essential requirements for each type of utilization (13).
The tests currently being carried out more or less systematically on these new species may give fairly complete information on their technical characteristics, particularly their physical and mechanical properties, their durability, their ease of working and conditions of putting into service. But it still appears that the technical criteria for each type of use have not always bean clearly defined. These vary much with markets and according to the requirements or equipment of the purchasers, and are often dominated by economic or commercial considerations, ease of supply and cost or yield, to say nothing of habits or questions of fashion.
It is, in other words, apparent, and fortunately so, that though for each use there may be optimal technical characteristics and technologies, their close concurrence is not necessary. In most cases, some tolerance or compensation is possible. A particular species considered as valid for a particular purpose in one country is not necessarily so in another.
Various attempts have been made to group species according to those criteria which are considered most important and which could serve as indicators or keys for the determination of use-potentialities. It must not be forgotten, however, that other species not included in such groups may nonetheless be used by industry despite some technical shortcomings. These might be compensated for by advantages of a different kind.
The interesting work of the Tokyo Experimental Forestry Station can be mentioned in this connection (14). Classification was according to 130 criteria on 67 species of wood from southeast Asia. A guide to the choice of species for solid-wood cabinet making, prepared by the Centre technique du bois in Paris (15), will help users in the choice of little-known species with a view to replacing traditionally used woods that have become rare or expensive.
Original graphic methods have likewise been proposed (16), as well as the use of computers to facilitate research or the compilation of data, provided always that they can be programmed with enough data.
There is no question of reviewing here the innumerable uses of wood and the technical properties they demand. A summary examination of the end-users of general purpose woods will suffice. These include cabinet making and decorative uses, plywood, buildings (framework, joinery, flooring), packing and public works, industrial wood, pulp wood, fibreboard, particle board.
It is commonplace to say that aesthetic criteria have brought about the evolution of cabinet-making and decoration, and that these are very subjective and depend upon fashion. This has been clearly shown by the considerable success of teak during the past 15 years or so. The Scandinavian designers and manufacturers of furniture have known how to exploit a success which probably cannot be repeated.
From time to time it happens that a new species is launched, additions to those select woods of assured value such as the rosewoods, mahoganies and woods with a similarity to walnut. Among species hitherto neglected which have made their mark in this way are Ovangkol or again Okwen, from Nigeria, which not long ago was being destroyed standing by poisoning! (3)
It is not out of place here to note that with the using-up of traditional species for cabinet-making, in particular the mahoganies and other red woods, some progress has been made in the colouring and finishing of wood. Thus certain species of pale or natural aspect easy to work and taking colour well, have a good future because they are more and more being used in replacement. This, for example, is being done with Aniegre and Abura among African woods and Ramin and Kauri (a conifer) from Asia and Australasia.
In any case, the requirements are more numerous and rigorous for species intended for cabinet-making from solid wood than for veneering or decoration. This is because very hard species or those with high content of mineral matter, like the rosewoods and Macassar ebony, can be sliced. Highly grained woods can be used as veneers, while cabinet-making from solid wood demands low shrinkage, fairly easy machining and sanding and no resin content which might sweat across the surface treatment.
MARKED FOR USE and for a particular purpose
It seems then that woods for solid wood cabinet-making will continue to represent the prime choice among those intended for sawing, and which are used mainly for visible woodwork. Some species still only slightly known, with or without aesthetic value, could be added to these. But one must not lose sight of the fact that, in de as developed countries at least, the production of furniture in series is based, as much for economic as for technical reasons, on face veneers on plywood or particle board. Solid wood furniture tends most often to become a luxury item.
In the same way, panelling in solid wood is being replaced by panels faced with decorative veneers.
The veneer industry, by way of contrast, has experienced a great expansion in tropical countries, notably in Brazil, in recent years. It has become the leading producer, because it economizes in primary raw material, and adds more value than sawing. This should be further developed.
Beyond doubt, this industry has been very exclusive regarding species, dimensions and quality of the logs that it uses. But today a certain relaxing of qualitative demands can be noticed. Many materials and coatings seeking to imitate wood have had too uniform an appearance. This has caused a greater appreciation o true wood veneers; so much so that wood is now presented with its natural defects, and wood material is accepted for decoration that would previously have been considered only as a second choice.
Two thirds of the volume of wood exported by tropical countries have hitherto been intended for the manufacture of plywood panels. This is a form of utilization which has developed at a high rate. The countries of southeast Asia have seen this growth increasing at 29 percent during the last four years. This was already the end use of nearly half the volume of logs exported from tropical Africa (mainly Gaboon, and Obeche or Wawa, to which were added smaller quantities of Ozigo, Ilomba, Afara, or Limba, and African Canarium) (4).
The tropical moist forests certainly provide light species of particular value for this use. Because of their homogeneous structure, their large diameters and their generally satisfactory conformation, these species lend themselves to peeling and give a yield of 45 to 52 percent. This is well above that obtained with woods from temperate countries, with the exception of the Douglas fir.
Even in tropical producer countries, the plywood industry has, however, concentrated upon a very limited number of species. These have proved their value, and their dimensions correspond to mill equipment. Also their appearance has become familiar in international commerce and to most of the end users. This is so, among others, for the various species grouped under the names of Philippine Mahogany, Meranti, Keruing and Virola.
Now that these main species are becoming scarce in accessible areas of the primary forest, others have to be found to supply the mills, and to take the place of the known species, and in the first instance, for the inside plies.
This applies particularly to Indonesia, and the Philippines where 60 other species could be used (19), and Nigeria where still only 14 species are used among about one hundred that would be suitable for peeling (3).
Construction absorbs in crude or roughly squared form, or as sawn-wood, the greater part of the timber used locally, and 35 to 40 percent of tropical woods imported into developed countries as logs, sawnwood or plywood. The size of this outlet should grow rapidly wherever tropical woods remain competitive with other construction materials. This is particularly so in tropical developing countries where there is a need for vastly increased new housing to cope with the population bulge, to say nothing about public or industrial buildings.
AMAZON VALLEY CEDAR durable, beautiful, valuable
Because of relatively high sale prices, higher than that of coniferous woods, the developed countries have not yet used appreciable quantities of tropical woods for structural purposes such as beams and rafters. Particular efforts to introduce tropical woods for structural use are being made in the United Kingdom notably by the Timber Research and Development Association. Because of their availability in large sizes and dimensions with few knots and defects, they are sought essentially for internal and external woodwork. It is the tropical woods such as Sipo and Meranti which have made it possible for wooden windows to maintain their competitive position against metal frames.
Regarding flooring, there has been rather a regression in developed countries, to the benefit of plastics and textiles.
The standards set up for these utilitarian purposes are generally not so stringent. There should be sufficient mechanical strength and good durability for trusses, moderate shrinkage and ease of machining and finishing for joinery or outside cladding. An acceptable natural durability is required; if this is lacking there should be the possibility of preserving the wood by impregnation. For flooring a moderate shrinkage is required, adequate durability and good resistance to wear and tear.
Packing remains, in spite of the competition of paper, cardboard and plastics, a very important usage, especially for marine shipment of merchandise. Developed countries have mainly made use of indigenous woods like poplar and pine, or imported coniferous woods, and in a supplementary way veneers or plywood of tropical woods (Obeche or Wawa, Gaboon, White Laurn). It is, however, very probable that as the trade between developed and developing countries grows, so too will the need for wooden cases, pallets and containers, usages which are often undemanding regarding quality. It should then be possible to use many tropical species among those now only slightly known, as well as inferior non-exportable sawnwood.
The expansion of means of communication and port installations in developing countries should rapidly increase the need for sleepers, electricity transmission poles, piles and large beams in hard woods. Besides the species so far used for such purposes, many other slightly known or unknown species could be suitable provided they were sufficiently durable or could be impregnated.
So far the use of tropical woods (or their felling or milling wastes) in a broken-down form, i.e. as fibres or chips, for the production of pulp, papers and cartons, or panels of fibreboard or particle board, has been at a low level for both technical and economic reasons. These industries, to be viable, must attain high levels of production. This raises problems of investment, of quality and quantity of supplies, and of market, all particularly difficult to resolve in tropical countries with heterogeneous forest and a low level of internal consumption.
Technical progress, however, makes it possible today to envisage in some regions the setting up of units of modest scale, particularly in southeast Asia and in Latin America (30). Trials have, moreover, shown that by grouping species according to density, a mixture can be used embracing quite a large number of those species not so far exploited. Thus a greater benefit from existing wood resources can be obtained while awaiting the possibility of more favourable artificial plantations.
The production of fibreboard has already been undertaken in a small number of tropical countries such as the Philippines, India, Thailand, Mexico and Colombia. It is less demanding on the quality of raw material to be ground than is paper pulp.
Small or medium sized units have thus been set up, preferably near sawmills, plywood mills or other wood conversion factories from which they use the wastes. This may include small quantities of sawdust and bark, occasionally supplemented with herbaceous plants, palm fronds, coconut fibre or straw.
India's three small mills (17) also make use of more than a dozen species from the rain forest, branchwood and other forest waste. The resulting panels are intended only for local consumption.
The setting up of fibreboard panel mills in tropical Africa has appeared much more risky because of the low level of local needs and the qualitative demands of the markets in developed countries (31).
It should be recalled that in Brazil and some other hot countries, fibreboard panels are largely products of artificial plantations (Eucalyptus or tropical pines) (27).
At first sight it would seem that the manufacture of particle board would be the simplest method of using a portion of the huge quantities of unexploited wood. Use could be made of little known species, badly shaped trees or those with dimensions too small for marketing as timber, as well as felling waste. Only some woods too dense or too abrasive for the cutting or chipping machines would have to be discarded.
Therefore almost all tropical forestry countries have included in their industrial development programmes, besides sawmills and plywood mills, factories for particle board based on waste, and supplemented by roundwood of various species (25, 26).
Particle board because of its accentuated comparatively low value/high volume ratio, was difficult to introduce into world-wide international trade. Therefore, particle board trade has been limited to exports within regions, notably within western Europe. For economic reasons we can expect that the establishment of export particle board mills will be restricted in the future.
The use of this new type of wood-based panel may run into difficulties under humid tropical climates, where solid wood and plywood are generally preferred. To give confidence to the users, it is necessary to control the quality of manufacture, especially regarding moisture content and resistance to insects and fungi. Protection can be assured by using phenolic glues and the incorporation of water repellents and preservatives.
With eight factories using 20 species of wood, India (17) seems to be the greatest consumer. Tropical Africa has scarcely started to become interested, yet the production of these panels in developed countries has in the last decade grown at a rate of nearly 20 percent a year.
There are many reasons why so many of the woody species found in the tropical moist forest remain neglected.
Some causes of this state of affairs are technical, others economic or commercial, and yet others purely psychological.
Scarcity or wide dispersion of species that are not well known, or lack of appeal because they are without decorative value or specific use, or because of difficulties of exploitation in their habitat (as in swamps or man-grove) are among reasons leading to neglect of certain species. But many other species, often fairly frequent in same types of forest stand, are quite accessible and are considered without value because of either too small or excessively large dimensions, bad conformation, particular or numerous faults, unfavourable properties of the wood, or difficulties arising in conversion or in being put into service (20).
SAWMILL TRAINEES IN CENTRAL AFRICA good machinery properly used can correct many defects
These disadvantages which explain the limited interest in these species, and which more or less justify their neglect, should be examined separately to determine if they are really inhibiting and how or to what extent they can be overcome.
Some species of the humid primeval forests often attain, mainly in tropical Africa, gigantic dimensions which makes felling hazardous; skidding, transport and conversion work with these trees are difficult operations with the usual equipment. As a result such giant trees have generally been left standing. Good examples are Cola gigantea, Pachyelasma tessmanni, and Klainedoxa gabonensis which can reach 7.5 metres in circumference. Many old and very large trees which are hollow or have rotten hearts remain standing in the forest.
Conversely, species normally with small diameters (e.g. less than 0.4 metres) have so been considered inexportable as logs. They are not exploited unless there is a local market for poles, sawnwood, pulpwood or fuelwood.
Some species have misshapen, high or strongly developed wing-shaped buttresses or deep grooves, fierce thorns, bark which causes irritation or gives off a fetid odour. All of this discourages exploitation.
Other specific defects of conformation include the stem no being cylindrical, curved unevenness, cannelures, and eccentricity in the core. Without making them quite useless, these faults depreciate the value of logs because they prevent peeling or seriously reduce the sawing yield. Species with a high proportion of such defects may often be left standing.
But these economic limitations vary from one region to another. They are modified according to the trends of external markets or the possibilities for local sales or conversion and the minimum diameter limits imposed for export or for local sawmills.
There are certain structural anomalies that occur in some species with irregular, spiral or veined grain. This may be apparent as peeling layers of bark, galls, spines or mottling which depreciate the value woods and make them difficult to plane and finish for modern usage.
Trees with such irregularities of grain, curled grain, crotches, gnarls and burrs, have indeed been and still are specially sought because they provide richly figured veneers. But figured wood is becoming more and more rare in areas that have already been felled over. They are also much less in demand than formerly because they do not lend themselves to industrial production of furniture in series. This calls for wood with a more uniform aspect which is easier to finish.
Spiral grain, which generally seems to be a fault of age, becomes distorted grain in sawmills. It causes warping and affects strength irregularities of growth or structure and sets up, in some species, tensions which causes logs to split or sawn timber to warp.
Light tropical species, or those of medium density, are among those most in demand on external markets. They are suitable for peeling, machine without difficulty, and their cost price per cubic metre is lower than far heavier woods. Unfortunately, for the most part these species are very liable to deterioration.
The sapwood, in the hours following felling, is subject to black-hole attacks by platypes and other Ambrosia beetles, and to various blemishes and decay. Later the sapwood in sawn and general purpose timber can become liable to powder-post beetle or Lyctus.
The export of logs of these species was long held back, as they often arrived in very poor condition. It has only been through the general adoption of preventative treatment with fungicides and insecticides applied at the proper time that they have attained their present important position. The number of these perishable species on the market was at first very small, but has grown appreciably in recent years.
There remain reservations regarding species of which the wood, even when dry, can still be attacked by Lyctus, or which in humid surroundings rot rapidly. They require onerous preservative treatment, provided they can be impregnated.
Heavy or very heavy woods have an economic handicap in that they cannot be floated and are more costly to transport. Also, their relative hardness discourages their use for general purposes so that these woods become restricted to very particular applications where their advantages lie in such qualities as high mechanical strength and durability.
It is the same with species with strong shrinkage, the logs of which cleave quickly at the ends or fissure deeply on the surface, so that they are often disdained. They are rarely exportable, and they have to be sawn locally and soon after felling.
The dimensional stability of sawn timber of tropical species is a criterion no less important if they are to be put to use in cold or temperate countries. There the pressure is considerably lower, especially in heated places, than in the countries of origin. Under these conditions highly grained species are unstable and they crack, split or warp. There is always difficulty in obtaining their acceptance, even at a reduced price in large works where these disadvantages would be less serious. Yet in a humid tropical climate where their moisture content remains close to saturation point they give excellent service.
In most forms of usage, not involving motion little importance is given to the mechanical qualities of wood, which generally exceed requirements. Among species which are little exploited there are plenty of hard tropical woods that have been shown by testing to have remarkable mechanical properties able to satisfy particular demands. In some regions, especially in southeast Asia, artisans know from experience or tradition the most suitable species for hardness, versatility, bending strength or even tendency to split. Except for some species whose wood lacks consistency or is too brittle or splits too readily, hardly any species is totally useless because of deficient mechanical properties. But there are woods for which the markets are too small to justify regular exploitation for use as an individual species.
The lowering of value and the neglect of a number of species of the tropical moist forest, which would otherwise be in demand, are caused above all by difficulties of sawing, seasoning or machining and to some extent by difficulties of finishing. These difficulties all have to be overcome before systematic exploitation can take place.
Some peel or slice badly because they are too hard or too fibrous. Others contain an appreciable quantity of silica or crystals which quickly blunt the saw teeth or the cutting edges of tools. Others have large quantities of resins making these woods pitchy which gives them a troublesome reputation, largely with artisans and small enterprises that are not equipped for such problems.
Seasoning of many tropical woods is often too slow, expensive or sensitive an operation particularly with hard woods and those subject to cracks, splits and seasoning checks, warping, internal shakes or collapse - so much so that some have given up using them.
Many soft woods which are hollow, fibrous or have contrary grain, will plane or mould badly and are difficult and take time to sand. Yet others with waxy wood, or containing antioxidant materials, or sweating with resin may take paint or standard varnishes badly. It must also be mentioned that some tropical woods are toxic, either because they contain alkaloids or other organic matter, and cause anaphylactic or anaclasic troubles for persons sensitive to this.
These difficulties, often exaggerated, have discredited some species. Yet, as will be seen below they can generally be overcome or reduced.
The unfavourable features which have so far prevented or held up the exploitation and regular use of some species of the tropical moist forest are known either from experience or from studies and tests. It is now important to find out by which means and to what extent these inconveniences can be overcome. Recently developed technology makes it possible to utilize certain of these species hitherto neglected.
There are, of course, many other considerations, often of a non-technical nature beyond the scope of this paper, which have a bearing on this subject. These can render inapplicable or unprofitable in the immediate or near future any solutions that could be proposed. But it must also not be forgotten that these conditions can change very quickly with the growing scarcity of species which up to now have been in greatest demand.
The developed countries have already seen the number of species imported expand noticeably in the last twenty years. But in volume, the newly marketed species do not yet represent more than modest quantities. They may occur infrequently in the forest or, being relatively unknown, they may still suffer from the distrust of many end users. Eventually a good number of these new species are adopted by well-informed industries who generally remain loyal once they know and have overcome the disadvantages.
Above all the developed countries have sought, and continue to expect from tropical forests, woods of fairly large diameters for slicing and peeling and able to provide ample sizes of sawnwood nearly free of knots and defects. It is among the little known species that we will find wood capable of meeting these needs and which could gain market acceptance.
The remainder may only find local outlets, or they would have to be put to the most advanced types of conversion locally or serve as raw material for panel production or paper pulp.
The situation varies considerably according to the country of production. Those which have only a low internal rate of consumption and little industry are at present heavily penalized by the heterogeneity of their forest, from which they can extract only selected woods for export. This is in direct contrast to conditions in heavily populated countries or those possessing or able to create integrated conversion industries. In the latter countries internal needs absorb large quantities of crude logs and sawnwood of all species and qualities, including small sizes of mixed species, so that even forest wastes can be used to manufacture panels or paper pulp and the major part of the production is disposed of locally.
Such is the case in some southeast Asian countries for example, in Africa (Nigeria) and in South America (Paraguay).
Depending upon the nature of the disadvantages of the tropical species that are hardly exploited, if at all, various technical solutions may be employed to resolve or adapt to the problems.
Woods that have until now been considered non-exportable as logs because of their low value or yield, would certainly acquire added value by local conversion to veneers, sawn timber, sleepers or semi-manufactured products. It would be necessary in many cases to adapt or augment the equipment of existing mills or factories whose capacity would have to be increased or new units installed.
The internal tensions occurring in some species could probably be released by ring barking before crosscutting the stem, or by immersion or steaming, and in sawing by successive cuts on opposite faces while making the machining allowances necessary to recut and straighten the warped pieces.
Provided they are correctly applied the very effective preservatives now available make it possible to exploit most delicate species. Such species were previously neglected because they are very quickly attacked by cryptogams and insects.
Repeated spraying of the logs, dipping of sawnwood as it comes from the saw and accelerated seasoning of sawnwood give temporary protection from these attacks and make possible export in good condition.
However, some tropical countries complain that the price of chemicals is too high and that they lack qualified staff to apply treatments. They hope for research that will result in simplified treatments. Also to be taken into account is the fact that these fragile woods remain of doubtful durability, even if they arrive at the end-user's yard in good condition owing to temporary preservative treatments. Before being put to use they may again have to be treated with a preservative insecticide if liable to attack by Lyctus beetle, and with fungicide if exposed to the weather or humidity.
These preservation treatments assume prime importance in the tropical countries themselves, for all uses where there is severe danger of decay or destruction by termites, such as piles, foundations and the framework of a dwelling house, not to mention sleepers and electricity transmission poles (18). These uses have traditionally been confined to a limited number of hard, and naturally durable, species. With over-exploitation these have come into short supply, as for example teak in Indonesia and Thailand, which had better been reserved for uses of higher value like furniture.
It is apparent that 80 to 85 percent of the species of the tropical forest are not durable in the local climate. Many producer countries should install vacuum pressure impregnation plants. The results obtained in Malaysia (21) can be quoted as an example. There today large quantities of beams and sawnwood of secondary species are treated and used for low-cost housing, vine stakes and railway sleepers from Kempas. Malaysia Keruing products are even exported.
However, all woods are not permeable, and vacuum pressure impregnation, which requires quite large installations and qualified personnel for their exploitation, is often considered too critical and difficult an operation. Simpler processes by osmosis or prolonged dipping in saline solution must also be developed. These might prove more economical even if not always so efficient.
High-density woods are clearly handicapped by the greater costs of handling and transport and because of this are no longer on external markets for utilitarian purposes not requiring great hardness or durability. Besides, working them is generally more difficult and requires more energy. This is why, except for limited volumes for some special uses, these species cannot be directed to other than the local market. There, used as partly squared flitches or roughly sawn, they are appreciated for special purposes such as public buildings, bridges, sleepers and for construction because of their durability and resistance to termites. On the other hand, they are: not very suitable for pulpwood and are only accepted in small quantity as part of a mixed species supply.
The objections made against a large number of secondary or slightly known species apply to logs and sawn timber affected by shakes, seasoning checks and warping, even in situ after having been put to work.
Opinions expressed about such species are often conflicting because the behaviour of these woods clearly depends upon the humidity conditions to which they are subjected. A particular wood seasoned naturally and used in a humid tropical climate can be accepted as stable, though it would withstand artificial drying poorly and would have greatly increased play in a centrally heated building in a cold or temperate climate.
To avoid too-rapid drying of logs awaiting conversion they should be kept submerged in water, or systematically sprinkled with water in log yards, and the ends of round billets should be coated with anti-cracking chemicals. Storage tanks help to prevent many losses resulting from cracks, cup-shakes and various forms of degeneration and would be valuable in sawmills and plywood mills.
Since shrinkage of sawnwood is greatest tangentially it is all important that grainy woods should be quarter or rift sawn. They should only be used in small sizes in assemblies following the essential rules of carpentry allowing play to operate freely without compromising the holding power of joints.
In manufactured products such as flooring blocks, panelling and mouldings, the woods should be used with predetermined moisture content corresponding as accurately as possible to the average humidity conditions in the place of use. This assumes that the place of use is known, that kilns with exact means of control are available and that watertight packing is used. This was certainly not the case with early supplies of planed woods arriving in Europe from Asia.
It is unlikely, therefore, that very grainy tropical woods could be exported without difficulty, in the form of finished products. This would have to be in the form of frieze lengths or dimensional elements made approximately to larger sizes than ultimately required.
In particular cases chemical treatment might be used to reduce the play of grainy wood. This is being studied in Indonesia (22) from where there are exports of large quantities of sculpture impregnated with polyethylene-glycol, or rendered water resistant to avoid subsequent cracking.
Seasoning techniques and kiln schedules have not been properly defined for tropical woods that are difficult to season artificially by standard methods. Some processing plants succeed in this better than others. It is necessary, then, for practical advice to be disseminated (18, 24). Much progress can no doubt be expected from less drastic methods than cold seasoning. Dutch ovens, solar seasoning or accelerated air or natural drying.
The machining of abrasive woods requires the use of specially adapted tools, stellite tipped saws, cutters in special steels, bars made up of carbide of tungsten on drills and cutter wheels.
Difficulties of finishing can generally be overcome by a preliminary scouring of waxy or resinous woods, the application of an impermeable sealer before painting or varnishing and the use of products incorporating a catalytic agent.
For external finishing on grainy woods it is useful to render them water-resistant. This reduces the risk of cracks and the cracking of films and non-filmy finishes are to be preferred to paints and varnishes.
Precautions are necessary when working and particularly when sanding species that are considered toxic. An exhaust fan for removal of sawdust and sanding dust is needed, as well as the wearing of filter masks.
Clearly it is possible to adapt to the defects of the slightly known tropical species or to reduce what may be objectionable qualities in them. The means for doing so often impose modifications or complications in the methods of exploitation, seasoning, working or application to actual usage. All of this can influence costs very much.
For logging companies to cut and deliver new species they have to be assured of adequate outlets. On the other hand, for users to remain interested in these woods, the preferred species should continue to be in short supply and at higher prices.
It was the shortage of Utile and resulting high prices for this species that led European importers and industries to substitute previously unknown species such as Danta and Abarco. This was done in spite of real difficulties encountered in using these two woods.
Bringing secondary or little known species into full use at the same time that other more acceptable species are still commercially available necessitates certain improvements or modifications of current practices in exploitation and industrial conversion.
The change-over from selective felling to systematic large-scale logging, if not clear felling, of stands of tropical moist forest, raises problems of infrastructure. The extraction of a much greater volume per hectare should bear less heavily on the cost per cubic metre than upon the equipment that has to be adapted or added to. Felling, primary conversion, haulage and transport of general purpose timber of low diameter or poor shape have to be covered as well as industrial wood of small sizes.
These problems seem relatively simple to resolve, given the experience gained in the intensive working of stands of all types. The existence of a large variety of equipment developed for this purpose means that there should be no reason for delay on this account.
However, it is necessary to put identification marks on every log; preservative treatment has to be applied since cutting of a much increased proportion of logs might result in their rotting easily, and they have to be quickly extracted from the forest. This requires more personnel and equipment in felling areas as well as the taking of precautions against the dangers of pollution by preservative chemicals.
It is difficult to find buyers in foreign markets for logs of secondary species and of less satisfactory shapes. Such species may also need preservative treatment. Serious efforts have had to be made by the tropical producers to ensure adequate care of logs through the various stages of handling and transport so that they will arrive in good condition. It is useful to have appropriate means of storage in the receiving ports. Ideally there should be sheds for fragile sawn timber and phytosanitary inspection by a service capable of renewing, when necessary, any deficient preservative treatment of logs and sawnwood.
LEARNING FOREST PRODUCTS UTILIZATION AT IBADAN development demands better management
In most of the tropical exporting countries the capacity of sawmills and plywood mills already installed is generally far below requirements. Their equipment is usually not adapted for the conversion of a growing volume of secondary or little known species of which dimensions and yield are mostly lower than those of woods normally handled.
It becomes necessary in most cases to augment equipment with new machines. Parallel production lines or subsidiary workshops may be required for sawing or peeling woods of smaller dimensions or that require different cutting methods or treatment.
Sawmills, for example, may need to be equipped with framesaws, "chip & saw" equipment and additional circular saws for quartering coarser grain species, or with doubling frames or additional resaws to recover offcuts and small sawnwood which will be produced in greater quantity.
The machines themselves will have to be modified or supplemented to deal with fibrous woods, or those which have confused grain, are harder, more abrasive or more resinous.
Efforts should be made to train good saw doctors and tool grinders capable of ensuring perfect maintenance of tools with stellite tips which are more expensive and more sensitive.
The sorting and classifying of sawn timber is necessarily more complicated. Distinctions may perhaps be required for the mode of cutting (slab, quarter, rift) depending upon the destination of grainy species. This may justify price differentials.
Mills producing sliced or peeled veneers for cabinet making, plywood or lightweight packing, might find it advantageous to install smaller machines. These should be suitable for the conversion of short logs of small diameter, while still giving satisfactory yield, e.g. automatic peelers of the Finnish type, peelers with telescopic spindles, backroll.
Steaming may become necessary for hard or cross-grained woods. The use of veneer sheets of smaller dimensions or lower quality, may mean complications in the manufacture of panels. These sheets would no doubt be used only for inside plies.
Whether working to satisfy internal needs or for export, secondary conversion workshops do exist in producer countries They usually only make use of a small number of species, machining them all in the same way with the same tools. But eventually they will have to use much more varied raw material. This will entail either sorting and grouping the species according to the work for which they are most suited, or so far as it is technically and commercially possible, trying to work the mixed species with multipurpose equipment capable of dealing with all the species without distinction.
It is probable that those seeking to produce for export will have to adopt the first solution. Many developed countries are unwilling to accept produce varying too much in appearance, hardness or colour. This is especially so if the wood is to remain visible as is generally the case when tropical woods are bought.
On local markets it can be otherwise. But it would probably be difficult to correctly plane or mould woods of very different texture and hardness using the same tools and the same working speeds.
Much progress has to be made before viable use can be made of species which have previously been neglected because of their low durability or their poor behaviour on exposure to weathering or variations in humidity. This applies also to the use without danger of sapwood, which is even rejected in many of the species already marketed.
What is needed here is research into the development of an artificial seasoning, and both surface and impregnation preservative treatments, and finishing treatments.
Much sawn timber of species liable to degeneration, or that are very grainy, cannot be exported unless given sufficient forced seasoning in order that they remain dry during marine transport. It is necessary to discard pieces that might be rejected on arrival or that might later turn out to be unserviceable because of a tendency to splitting, seasoning checking or warping. Such preliminary seasoning makes it possible to sell timber of hard woods for which air-drying would otherwise be prolonged, and it means that the wood becomes usable much more quickly.
It is necessary, then, to create or develop seasoning installations for accelerated drying (e.g. solar drying under plastic covers) or new artificial drying according to standard processes by the circulation of hot air. Or new methods might be developed (condensation, heat pumps, vacuum or chemical processes) or adapted to local economic conditions and to the more or less refractory character of the wood to be dried.
Preservative treatment is of particular importance in tropical countries where destructive agents are both numerous and very active. It is clear that to maintain and develop the use of wood, in construction and in public works in particular, it is necessary that it should have sufficient durability while still remaining economically competitive with iron or concrete.
The increase in plants for the preservative treatment of wood by injection or deep impregnation, still far from numerous, becomes necessary because woods of natural durability are insufficient. The latter represent but 15 percent or less of standing volume in most forest stands. Needs will necessarily grow with population growth and social and industrial progress in producer countries. These countries might also export poles, sleepers, beams and construction wood after treatment, to neighbouring countries short of forest resources.
Preservation centres could also possibly move on to fireproofing of construction wood. This will most likely become obligatory one day for public buildings.
The impregnation of wood by osmosis or by prolonged dipping in saline solution, which requires a lower level of investment, could in many cases replace vacuum pressure impregnation when the woods are sufficiently permeable.
For joinery and furniture wood, which is less exposed but remains liable to Lyctus, a simple impregnation in a solution of boron salts by the hot and cold process has proved efficient. It gives immunity and makes possible the use of healthy sapwood, with all the saving in material that this represents.
It should be possible in many developing countries of the tropics to set up wood-using industries capable of substituting imported products with ones made from local woods that have so far been little used. First a sufficiently large local outlet must be established, or complementary export possibilities found. Examples are the recent creation of plants for packaging materials, factories for fruits and other products e.g. chests for tea, spices, pineapple, etc., manufacture of matches or matchboxes, panels and binders, wood-wool cement mixtures such as wood-wool board and Callocrete.
But most in this line can be expected from products derived from mechanical or chemical disintegration of wood in order to use integrally, in mixture (25, 26) all or at least most of the species of the tropical moist forest not suitable for peeling or sawing. This would include particle board, fibre-board or paper pulp.
So far only a small number of fibreboard mills exist in the tropics, but this industry, too, can adapt itself to the use of a large number of wood species, provided the process uses an alkaline-predigestion system. It can incorporate waste wood and agricultural residues, including straw. New installations can in the first instance be expected in Southeast Asia (29, 30, 31).
In tropical regions of high population density the establishment of new units can be expected and encouraged to use "all comers," small wood sizes, forest waste currently being left in the forest, possibly mixed with other vegetable material and agricultural waste.
It is to be concluded, therefore, that more complete exploitation of the resource so far badly utilized, available in the humid tropical forest, is not only an essential and urgent need to meet the threat of a world-wide wood shortage and help the development of those countries possessing these forests, but should also lead to gradually improving forest management with a view to attaining a sustained and higher production of more valuable woods.
Some important organizations for tropical timber research
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AUSTRALIA Division of Forest Products, BELGIUM Laboratoire forestier BRAZIL Universidad do Brasilia COSTA RICA Laboratorio de Productos Forestales, FRANCE Centre technique forestier tropical, FEDERAL REPUBLIC OF GERMANY Bundesforschungsanstalt für Forst - und Holzwirtschaft, GHANA Forest Products Research Institute, INDIA Forest Research Institute and Colleges, JAPAN Government Forest Experiment Station, Meguro, MADAGASCAR Centre technique forestier tropical, MALAYSIA Forest Research Institute, THE NETHERLANDS Houtinstituut, NIGERIA Federal Department of Forest Research, PHILIPPINES Forest Products Research Institute, PORTUGAL Laboratorio de Histologia e Technologia SPAIN Instituto Forestal de Investigaciones y Experiencias, THAILAND Royal Forest Department, UNITED KINGDOM Building Research Establishment, UNITED STATES OF AMERICA Forest Products Laboratory, VENEZUELA Instituto Forestal Latino-Americano de |
