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The utilization of low-quality tropical timber

K.F.S. King

K.F.S. KING is FAO Assistant Director-General in charge of the Forestry Department. This article is from an address he delivered to the 1977 General Meeting of the Commonwealth Forestry Association in London.

In its most recent publications on the marketing of tropical wood "FAO" defines as "commercial" all those species of the tropics that are produced in quantities of more than a thousand cubic metres All other species are defined as "lesser-used", if they are either produced in quantities below one thousand cubic metres per year, or, if they are not used commercially, they have been identified as having potential for use in the form of sawnwood, veneer or plywood. It is assumed that the number of really unknown wood species is relatively small. FAO concludes that in west and central Africa there are 105 "commercial" wood species and 112 that are "lesser-used"; in southeast Asia there are 634 "commercial" species and 465 that are "lesser-used"; and in tropical South America there are 210 "commercial" species and 263 "lesser-used" species. In short, in the three major wood-producing regions in the developing world, 949 species have been classified as "commercial" and 840 as "lesser-used". About half the species are not utilized, or are flagrantly under-utilized (Erfurth, 1976).

The consequences of this inability to utilize the total resource of the tropical forest are well known. Production costs are, of course, high. Furthermore, the expense of regenerating either natural or artificial forests is exorbitant because there are too many trees left to be removed. Perhaps more important is the enormous waste. The world cannot continue to afford the clearing and burning and poisoning of tram practiced by foresters in almost every tropical country that is fortunate enough to possess natural high forests.

It is well known that what is considered to be low-grade wood, say, in a timber concession in Sarawak may be accepted as high-grade wood, say, in central India. In addition, a species may be low grade for one type of end use, but superior in quality for another. Every specific situation produces its own concept of quality, of desirability, of grade in its broadest sense.

We may therefore define low-grade wood as wood which, in a given situation, is not utilized, because:

· The physical and chemical qualities of the species are considered unsuitable for products for which there is effective demand.

· There is no adequate technology available for its harvesting and/or subsequent processing.

· The economics of utilization are, in general, unattractive and unrewarding to investors.

· The marketing infrastructure and marketing systems in the area or country are inefficient.

Certain implications of the above should be emphasized. First, any one of these negative factors will be sufficient to prevent the utilization of particular species and/or certain types of wood. Second, the acceptance or non-acceptance of a species or of certain qualities of wood can change with time. Third, this change may well be dependent upon circumstances which are not peculiar to the forestry or forest industries sector, e.g., the socioeconomic climate of the nation, the establishment of tariff barriers by importing countries against certain types of wood and wood products, the general level of technology available in a particular country, the ease of transferring technology from one country to another, and so on. Fourth, whether a particular species or type of wood is thought to be low grade or not is often dependent upon the interplay of socio-economic and physico-chemical factors.

It follows from all this that there can rarely be a simple answer to the problem of the utilization of low-grade wood. The attack has to be made on several fronts, and the approach to the problem must be systematic.

The method which has been advocated most often for utilizing and marketing the low-grade wood of tropical forests may be summarized as follows:

1. Conduct an inventory of all the species (including, in particular, those that are not well known) so that their location and frequency may be ascertained.

2. Investigate the physical properties of the lesser-used species.

3. Classify these species according to their utilization qualities, particularly with regard to their ultimate use possibilities.

4. Group those species which possess similar physical characteristics, but which singly do not occur in commercial quantity.

LOGGING IN A HIGH FOREST IN INDONESIA - how to use what is "useless"

There is much to commend this approach. However, the many attempts which have been made by developing countries to sell groups of species, or even single lesser-used species which are in abundant supply, to the industrialized world have, in the main, been most unsuccessful. They have failed for two basic reasons.

First, sales of these new species have often been attempted through distributors. By far the greatest amount of tropical timber imported by the developed industrialized countries is used in the construction and furniture industries. However, these two classes of industry are really quite heterogeneous aggregates of a variety of specific uses. This is especially true for the construction class, in which the wood properties required for such uses as window frames, sills, doors, flooring, framing, panelling, shelving, cup boards, and so on, differ greatly and would require a different range of suitable species in each case. With much the same thing occurring in all the broad use classes that are commonly recognized, the heterogeneity at the demand end could almost match the heterogeneity at the supply end.

Such a varied pattern of end uses, served as they are by highly fragmented industries, inevitably means that the final processing stage of tropical timber occur in a very large number served as they are by highly fragmented industries, inevitably means that the final processing stages of tropical timber occur in a very large number of individual units, with specialized needs, methods and outlets. Tropical timber supplies thus contact the consumer at a somewhat diffuse, amorphous and mobile boundary.

The multi-faceted characteristic of the marketing system lies at the very heart of the problem of the lesser-used species. No matter how much research is conducted into the availability and properties of these species, no matter how much developmental work is applied to their processing and use, these will be to little avail, unless they affect their end-use demand. At present, the opportunity for introducing new species to the market lies much closer to the parties operating toward the user end of the distribution chain than it does to the producer end. The producer normally has contact only with the distributors. He almost never meets the consumers. But this contact with the consumer is essential. AU future attempts to sell new species will fail if the developing countries do not establish marketing and market research units in the larger consuming countries. This may be done by the individual country or, more rationally, through producer associations which have been established on a regional or sub-regional basis.

The second reason for the general lack of success in marketing the lesser-used species of the tropics in the developed countries, through the methods traditionally advocated, lies in the tendency to sell logs or sawn timber. This predilection of the exporting developing countries for logs and sawn timber is in part a function of custom, and in part the consequence of the tariff barriers which have been established by the governments of many developed countries against the importation of manufactured goods. Be that as it may, it has been demonstrated that the general, ultimate consumer in the developed, industrialized countries is more likely to purchase an article of furniture, or a cupboard, or prefabricated window frames and sills that are constructed from lesser-used species, than are those who actually make these artifacts in the developed world, or those who distribute to them. The consumer is more likely to buy goods manufactured from the lesser known species. It follows, therefore, that apart from the benefits of having the value added through processing accruing in the country of origin, the opportunities for entering new markets with new species will be greatly improved if emphasis is shifted from logs and sawn timber to the finished or semi finished article.

The world cannot afford the clearing burning and poisoning of trees practiced by foresters in almost every tropical fortunate enough to possess natural high forests.

This will, of course, require investment and technical knowledge. Perhaps more important, it will require those developing countries, which wish to control the exploitation of their natural resources and the development of the industries based on these resources, to establish trans-national corporations. The reach of the owners of the wood raw material must stretch across the oceans to the developed countries. The industries should be vertically integrated, the up-stream activities being in the developing countries, the down-stream in the developed countries, in the closest contact with the consumer. Whatever the ownership pattern and the division of responsibilities, it is essential that there be continuous links starting with the extraction of the raw material, encompassing the primary, secondary and tertiary stages of processing, and ending with marketing, if there is going to be a real breakthrough in the marketing of lesser-known species in overseas countries.

So far we have assumed that the low-grade wood was destined for overseas markets. Often, however, the local market provides a much better environment for the utilization, of low-grade wood. The experience of one company in Nigeria might serve to illustrate some of the conditions under which the utilization of species, which were formerly rejected, might occur.

The demand for wood and wood products is increasing rapidly in Nigeria. Aware of this, this company, which in the past produced mainly for export, saw the opportunity for utilizing wood more efficiently for sale to the local inhabitants. They discovered that the species identity was subordinate, so far as the customer was concerned, to product performance. Consequently, they now produce, for example, timber panel components for the construction of houses and other buildings. These components are made of mixed species selected for their physical reliability. The wood is treated with preservative. Similarly, doors and window frames are produced by using a multiplicity of species, often of different colours. These find ready acceptance where it is intended to paint the product.

It must not be assumed that a country has to be experiencing an economic boom for its citizens to accept so-called low-grade wood. In Guyana, where for centuries green-heart, Ocotea rodiaei Schomb. was the preferred species, the local population now utilize a great range of wood species. This transference of taste has been achieved through a painstaking study of the physical characteristics of several dozens of wood species, by publicizing their properties to the ultimate consumer, and by ensuring, through proper seasoning, for example, that the performance of those species which were being promoted, met the standards which had been claimed for them.

Increasingly, similar success stories are being reported from all over the world. They all support the contention that, physical investigations of the wood properties having been conducted, the key to the utilization of low-grade timber lies with appreciating the needs of the consumer, catering to those needs, and convincing him that supplies and standards would be maintained.

I have given so much attention to promoting the use of the lesser-utilized species, because there are doubts about the procedures normally advocated. It is my conviction that if contact is made with the consumer, and if an analysis is made of his requirements, we will be well on the way to infiltrating the overseas and local markets.

However, the main advances in the utilization of low-grade wood will not be achieved through the adoption of more efficient marketing systems, but through the improvement and the application of existing technology.

Some examples from the relatively unsophisticated fields of seasoning, preservation and building techniques might be useful.


Before the reconditioning process for the removal of collapse (that is, excessive, catastrophic shrinkage) in eucalypts was discovered, half the standing volume of eucalypt timber in Australia was considered "low grade", and to have no value as sawn wood. Through reconditioning, whereby the collapsed wood is steamed after seasoning, all of this timber, as well as other "collapse-susceptible species", is now utilized.


Examples are so well known in the field of preservation that it may be tedious to quote any here. It should be stressed, however, that preservation is probably the most powerful technological process for bringing low-grade species of the tropical forests into use.

If developing countries export more finished and semi-finished products, they can keep the value added and utilize lesser-known species at the same time.

For example, in New Guinea the Government has decreed that all sawn timber produced for housing be treated with preservatives. Most of the production is treated by a simple dip diffusion salt mixture, which confers sufficient protection to enable any species, however perishable or however termite-susceptible it may be in its natural state, to be used permanently in house construction, provided the wood is not in contact with the soil. The result of this system is that, from the sawmilling point of view, the problem of secondary or unused species has virtually ceased to exist in that country.

Improved building methods

In zones where subterranean termites occur it was previously necessary to use for house construction timber which was naturally immune to attack. Now it is possible to eliminate subterranean termite attack for periods of far more than 30 years by poisoning the soil beneath the building, using organic chlorinated insecticides. Thus, the range of species for house building is extended by eliminating "resistance to subterranean termites" as a property required of house building timbers. However, in areas where dry wood termites (Cryptotermes) or Lyctus borers are a hazard, preservation by diffusion or impregnation of those species which have low resistance to these pests is still required.

Traditionally, timbers used for house framing have low shrinkage characteristics, and are utilized in the unseasoned state. In many countries, particularly in the tropics, large volumes of hardwood species are left unused, even though they possess the necessary strength and workability for house construction. This, because of their high shrinkage characteristics. It has now been found possible, through the adaption of certain building practices, to broaden the range of hardwood species which may be used for framing in the unseasoned state, even though they have high shrinkage factors.

The system is to change the method of frame construction, so that the effects of the shrinkage of the timber may be minimized.

For example, in utilizing beams over a wide window opening, it is necessary to select a beam of about 10 or 12 inches in thickness to carry the superimposed roof load. When such a beam is made of high shrinkage unseasoned hardwood, and is framed in the conventional manner, the subsequent shrinkage may lower the roof line by up to one inch. This is unsightly and causes structural and finishing problems. By changing the framing method, the problem is overcome. The technique consists in nailing a heavy batten at the bottom edge of the lintel beam and arranging the short jack-studs to be supported at this batten. The beam can then shrink freely away from the top edge, without causing any distortion in the frame.

Other details which may be mentioned are the use of flooring not more than 10 cm (4 inches) wide in the green state to reduce the shrinkage gap between boards on seasoning and the use of cladding, not more than 10 to 12.5 cm (4 or 5 inches) wide, fixed with a single nail at the bottom edge at each stud so that shrinkage does not cause splits to develop. Also, by using a wide overlap 1.5 cm (about half an inch) the cladding remains leak-proof after shrinkage. Other details consist in the use of mixed frames comprising seasoned wood for such items as corner studs, ceiling joists and lintel beams and useasoned wood for the remainder. In addition, a mixed frame of softwood and hardwood may be used. The lower shrinkage softwood is used in critical parts where excessive shrinkage can cause problems.

By these methods the range of species, which can be used in house construction, has widened in a typical situation from a few to almost the run of the forest.

Pulp and paper

There are many other examples. The point I wish to stress, and which I shall repeat often, is that in many cases the focal point for action in the greater utilization of low-grade wood is outside of the forestry profession proper.

It is my also that the full utilization of low-grade wood is inextricably linked to the development of forest industries. Let us examine the roles of the pulp and paper industry, and the wood-based panels industry in the future utilization of low-grade wood.

The pulp and paper industry is the most important single consumer of industrial wood. It has been forecast that by 1985 the world's consumption of industrial wood will be 1900 million cubic metres, of which the pulp and paper industry will consume 800 million cubic metres.

The developing countries possess 55 percent of the forest land of the world, but produce only 6 percent of the paper which the world consumes.

Despite the fact that research in the utilization of tropical hardwoods has been conducted for several decades, in only three countries are mixed tropical hardwoods used as the sole wood resource base for the production of paper.

As is known, because there existed ample supplies of long-fibred pulp in the developed temperate world, at least until the early 1950s, there was a reluctance on the part of the pulp and paper industry to utilize short-fibred hardwood pulp for the production of paper. However, when it appeared to some industrialists that the time would arise when there would be a shortage of long-fibred pulpwood, it was discovered that pulps gleaned from birch, beech, the eucalypts, and other species were eminently suitable for the production of certain grades of paper. Thereafter, the technology for utilizing short-fibred pulps from temperate hardwood species developed rapidly.

Attention was also being paid to the possibility of utilizing tropical hardwoods for the production of pulp and paper. Unfortunately, the pulping characteristics of the species were at first studied individually, which did not make very much sense because it was difficult to harvest individual species from the mixed forest economically. It was also difficult, in many cases, to obtain a sufficient number of trees of one species to supply a pulp mill of a reasonable size. It is only since pulping tests, which embraced many species in mixture, were undertaken and found successful, that the development of this aspect of forest industries advanced somewhat.

To market low grade timber successfully you have to appreciate the consumer's needs and give assurances that supplies and standards will be maintained.

However, it was necessary to destroy some deeply ingrained prejudices, and to demonstrate that some apparently logical assumptions were unfounded. For example, it was long believed that high density species were not desirable for pulping. It was also assumed that consumption of chemicals would be high and would be related to the requirements of the species most difficult to cook. It was also solemnly affirmed that, in cooking the mixture, some woods will be over-cooked and others under-cooked. Practice has shown, however, that the consumption of chemicals is the same for mixed tropical hardwoods as for the conventional hardwoods, that the quality of pulp from such mixed hardwoods is fully acceptable and that for some grades of paper mixed hardwoods are even more desirable than the traditional hardwoods. It seems that the wide range of values which interact in the pulping process of the mixed wood species contributes to this unexpectedly favourable result of the pulping process. Of course, there are still some problems that are connected with some species: for example, the high wear of knives occasioned by extra-hard species, or the problems caused by species rich in extractives and silica. But these are by no means insurmountable, and may merely entail the removal of such species if they occur in significant quantities. The point of importance is that when the processes of utilizing mixed tropical hardwoods for pulp and paper become generally acceptable, we will have gone a long way toward solving the problem of the utilization of low-grade wood.

A shortage in the supply of conventional raw materials, which has been caused by competition from other types of forest industries, and by the increasing demands of the whole panel products sub-sector, has forced the wood-based panel industry to utilize a wider range of raw material, and to utilize more efficiently whatever raw material is available.

The plywood industry has traditionally been the most demanding - in terms of quality - of the wood-based panel industries. However, even in this industry the so-called lesser-used species are being more utilized.

Wood-based panels

There are many reasons why some peelable species are not considered suitable for plywood manufacture. Some possess low strength properties and are prone to mechanical damage, which makes them unacceptable, for example, for furniture. Others have a high sugar content and are not therefore utilizable for concrete forms, for example. Some species have colours which are not found attractive for certain end uses or which tend to get discoloured when exposed to sunlight.

In all these cases veneers can be used as cores. The thicker the core the greater the volume of "lesser-used" species that may be used in the plywood industry. Moreover, in certain cases veneers with unattractive appearance can be coated or laminated, thus making it possible to use them as top veneers in plywood. Lamination may also permit the use of sugar-rich wood in surface layers on concrete forms by providing barriers that are impenetrable to organisms seeking sugar.

In utilizing some wood species for plywood manufacture, processing difficulties sometimes occur. These include the falling apart of veneers with special grain formation, drying failures, and gluing problems. Some of these difficulties may be overcome. For example, in certain cases drying problems caused by the uneven distribution of moisture (for example in Terminalia spp.) may be solved by passing the veneer more than once through the dryer. Again, certain wood species have a chemical reaction which inhibits a satisfactory bond. A quick chemical test has been developed by identifying woods which may create problems in gluing or in leeching out extractives. Once these species are identified, it is possible to adjust process variables such as type of adhesive, pressing cycle, and so on, to overcome the problems.

Wood species which are peelable but which occur in small quantities should be used either as plywood cores or as surface veneers, provided a final product such as flush doors is made in the same factory. These can be painted and a customer will not, therefore, observe the different appearances of the various species of surface veneer which have in-en used.

All attempts to sell new species will fail if developing countries do not establish marketing and market research units in the larger consuming countries. Main advances in this field will be through improvement and application of existing technology. Engineers, chemists and big-chemists should attack the problem.

It should also be noted that the old requirement for large diameters for plywood manufacture is now no longer valid, and it is possible to utilize logs which a decade ago were considered to be of low quality. Nowadays, logs with as small a diameter as 150 mm (6 inches) can be peeled down to a core diameter of only 60 to 65 mm (2.4 to 2.6 inches). This has become possible because of the development of special lathes and of improved drying and gluing techniques.

In recent years there have been considerable advances in the technology of particle board and fibreboard manufacture As a result, almost any size and shape of mill and forest residues and an extremely wide range of wood species can now be utilized in these processes.

The particle board industry throughout the world now uses low grades of industrial residues, including sawdust and sander dust, mixtures of softwoods and hardwoods and mixtures of tropical species. Indeed, one particle board mill in Peru utilizes up to 45 hardwood species. Since this is the most rapidly developing sub-sector of forest industries (the growth rate of the particle board industry has been 9 to 10 percent annually over the decade ending in 1974), increasing volumes of low-quality wood are finding an outlet. The manufacturing process is highly flexible and allows for various adjustments in response to different qualities of raw material. The use of the heterogeneous mixtures of residues in this industry is possible because of the diverse types of flaking machines that can be used for their conversion into suitable particles: drum flakers, ring flakers, screen ring refiners, pressure refiners, etc. Thinnings from plantations which, in the past, posed serious problems of disposal in many parts of the world can now be processed with advantage in particle board mills.

The fibreboard industry is even less sensitive to low-quality and mixed raw material input than the particle board industry. The trend throughout the world in this industry is to use more mill residues, a higher proportion of unbarked roundwood, more mixed hardwoods and more tropical hardwoods. Because, in the past, the fibreboard industry found it difficult to compete with the pulp industry, it was forced to explore the possibility of utilizing an ever-increasing proportion of lesser-known wood species and to develop technological adjustments accordingly. This it has done with success. In the United States nearly all new hardboard plants and many of the older ones are using more and more mixed hardwoods and fewer coniferous species.

New products

A range of products is being developed, or has been developed, which will gradually provide new outlets for low-quality wood.

One such product is composite plywood or particle-core plywood. This consists of a core made of particles, while the surface layers are made of veneer. The main reason for this development was the desire to obtain a substantially greater volume of panels for typical plywood applications from the same volume of logs, when compared with conventional plywood. In this process, comparatively large quantities of residues and low-quality wood could be used for the core layer.

Another new product is "press-lam" developed by the Forest Products Laboratory of the U.S. Forest Service in Madison, Wisconsin. The technique used here is largely that employed by the plywood industry: rotary cut veneers of up to 12 mm thickness are press-dried and laminated into continuous sheets while still hot. They are subsequently sawn into sizes corresponding to constructional lumber. The yield from raw material is higher when compared to sawing and a high-quality product is obtained from small-sized, low-quality logs. It is in the nature of this process that all wood defects, and all those parts of wood which contain undesirable characteristics can be cut out, and the "clean" veneer glued together into high-quality sheets of predetermined strength and other characteristics.

A product which has gained considerable importance in the last years and which seems destined to play an increasing role on the market is wafer-board. This board is made of large flakes glued together with powdered phenol-formaldehyde resin. It is used for both exterior and interior applications in housing (mainly in Canada) where it competes directly with softwood plywood. The initial success of this board was caused, among other things, by the fact that it utilized as raw material a wood species for which there was little other commercial demand: aspen. However, other low and medium density wood species are also suitable for the manufacture of wafer-board. The product is of great interest to countries which have a demand for structural building panels but which lack suitable high-quality raw materials for plywood production.

Structural flakeboards with oriented flakes or strands are a great step forward in the development of woodbased panels with predetermined engineering properties and a favourable strength to weight ratio. In such boards, wood chips or strands or flakes are aligned (by mechanical or electrostatic means) to form a one-layer board with its strength in one direction or a three-layer board, in which particles of the core layer are oriented at right angles to the particles in the surface layers. This type of panel is now in direct compensation with plywood althought it is made of much lower quality raw material.

A whole range of other panel products based on low-quality wood and on the orientation of particles or fibres has also been developed or is now in various stages of development. There are hardboards with oriented fibres, cement bonded particle boards with oriented particles, and so on. These products constitute a large and promising outlet for low-quality wood in the future.

Reservoir of cellulose

But it is not only the panel industries and their technologies that can offer - now and in the future - high-quality products from low-grade wood. Other segments of the mechanical wood processing industry possess technologies and machinery which provide similar opportunities. Production lines have been in existence for some time which can produce continuous flooring boards from small pieces of wood, not necessarily of the same species. Similarly, there are lines which produce joinery elements from short planks, from which defects were cut out. The possibilities for the utilization of low-grade wood, in this area of forest industries, seem infinite.

One final word with regard to possibilities for the utilization of low-grade wood. It seems evident that in the future wood will be used in continually greater proportions and in various forms, as a source of fuel. Perhaps the main types of fuel which the forests will provide will be in the form of fuelwood and charcoal, but it is not at all improbable that liquid fuels and gases will be obtained in increasing quantities from our forests, thus utilizing species and types of wood that are now considered low grade. Moreover, in many countries already, low-grade wood is being utilized to produce charcoal for industrial use. The economics of such an enterprise seem promising and there is much hope that the extension of this practice to mixed tropical forests may result in the fuller utilization of the wood found there.

We must look at our forests not merely as a source of sawnwood and plywood, but as a complex natural resource capable of yielding a wide variety of products. We must conceive of our forests as a reservoir of cellulose. We must understand that the categories of wood use are not closed, and that man's imagination and technical competence are such that more and more uses are being found for our wood. We must appreciate that technological advances, not only in the field of forest industries, but in all fields, have contributed immensely, and will continue to contribute, to the solution of the problem of the utilization of low-grade wood. Indeed, I suggest that there is really, technically speaking, no problem. However, it must be emphasized that if there is a problem it is not in the forest. We must seek new building methods and there is need for imaginative adaptation and expansion of existing technologies. Above all, the solution to problems of greater utilization of low-grade timbers lies in the maceration, the pulverization, the fragmentation of the wood; in the use of wood after it has been reconstituted from pulp, from fibre and from particles. The attack on the problem of low-grade wood should be made by the engineers, the chemists and the big-chemists.

If I were practicing silviculture I would not eliminate from my forests species that are now considered unsalable. For I am of the opinion that by the end of this century - in most cases less than a rotation - the species now considered weeds, and the malformed trees now considered undesirable, will all be utilized, in a world of shrinking resources.


ERFURTH, T. 1976. Product development and the choice and effective application of promotional measures to advance the wider use of products from the tropical moist forest. FAO, Rome.

ERFURTH, T. and RUSCHE H. 1976. The marketing of tropical wood. FAO. Rome.

TOWLER, R.W. 1975. The possibilities of increased consumption of the lesser known tropical hardwood species. Commonwealth Forestry Review. Vol. 54(3) and (4), Nos. 161 and 162.

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