Robert L. Youngs
ROBERT L. YOUNGS is Director of the U.S. Forest Products Laboratory maintained in Madison, Wis., by the Forest Service, U.S. Department of Agriculture, in cooperation with the University of Wisconsin.
In the New World, low-altitude wet evergreen tropical forests cover some 5 million square kilometres, and any one forest may support hundreds of tree species. Timber volumes may range from 150 to 300 cubic metres per hectare. Industrial feelings, however, are highly selective, and the harvest is often only 3 to 10 percent of this volume.
Most of the production of a large integrated manufacturing complex in the Guiana region of South America draws on only five species; 90 percent of roundwood exports were recently in two species; 95 percent of sawnwood exports in three species; and all plywood production and trade in one. Yet, technical data on the properties of some 50 species are well known, and half of these are classified as readily available in quantity.
High species selectivity is not unique to the Americas, for 90 percent of West African log trade out of Nigeria has been in only six species. Harvest by skimming is even more obvious in the rich forests of southeast Asia. For example, about 3 900 tree species have been described in the Philippines, but less than 100 reach local markets, and export trade is dominated by only seven.
Traditionally, our woodworking industries have been based on the "difference approach." Forests everywhere have been surveyed and screened to find species that could perform best for specific end uses. Just now, there is a movement, not only toward the development of "whole-tree" utilization systems, but also toward species-tolerant processes and products. The array of species feeding into pulp mills is a long step from the spruce-fir-poplar limitations of just a few years ago. Plywood sheets are overlaid, embossed, grained, stained, and marketed with no identification other than a decorator's "green cascade" or "sunshine gold." Certainly, particle board and fibreboard panels do not have botanical tags. Further development of machine stress grading can result in wood components of any species and grade being assigned to optimum cross-sectional and longitudinal positions in structural elements for an efficient and certifiable performance. For the heterogeneous lowland humid tropical forests, a more intensive pursuit of nontaxonomic or non-specific systems could permit a more flexible harvest of the timber resource.
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Use more, waste less |
EXAMINING A HUMID TROPICAL FOREST - nature, more varied than trade
Mixed though the lowland humid tropical forests are, similarities may appear in composition and form between widely dispersed timber stands. L.R. Holdridge at the Tropical Science Center, San Jose, Costa Rica, has quantified the forest shape or physiognomy based on life zones defined by rainfall, temperature, and evapo-transpiration. If it can be demonstrated that the total wood resource, as well as the forest form, reflects the environmental conditions of a life zone, then processes can be developed based on this particular wood mix, regardless of species composition. Results would be applicable to large forest tracts, wherever located, that have the same life zone classification.
Recent studies at the U.S. Forest Products Laboratory, Madison, Wisconsin, show that wood specific-gravity distribution patterns for tropical American species are indeed unique to certain Holdridge life zones. Specific gravity was chosen for this first probe because it correlates well with such important wood characteristics as mechanical strength, shrinkage, gluability, screw-and-nail-holding properties, cutting forces required in machining, and paper-sheet formation.
In the low rainfall (1000 to 2000 mm) tropical dry-premontane moist life zones species distribution is fairly uniform in all density classes from less than 0.30 to over 0.69. Within the tropical moist-premontane wet life zones (2 000 to 4 000-mm rainfall range), a high proportion of the species are generating very heavy timbers. The abundant rainfall (4 000 to 8 000 mm) of the tropical wet-premontane rain life zones favours species in the moderate density class of 0.40 to 0.49. This research work establishes a significant base for sampling in developing non-species related processes and can also suggest the most suitable locations for industrial complexes that depend on timber.
Present timber-harvesting systems for primary species could be encouraged if they perpetuated these favoured trees. Most often they do not. An "any-tree" harvest can avoid many forest management problems that are still not solvable. Certainly, the site would be well prepared for high-yield plantation cultures or manipulation of pioneer species; but insensitive processes could also be catastrophic if raw material harvests are not tightly controlled or restrained where environmental impacts would be intolerable.
The Forest Products Laboratory, under agreement with the U.S. Agency for International Development, started a three-year cooperative research project early in 1975. The project has two related research objectives aimed at full-scale production of forest products in the lesser developed areas of the tropics.
Objective No. 1: through research, development, and pilot plant testing, to develop a technical and economic processing system for making pulp, paper, and related products from naturally occurring mixtures of tropical hardwoods. Such systems would be subject to the test of full feasibility and appropriate technology. Residues not acceptable for any of the forest products will be used to meet the energy needs of the processing system.
Objective No. 2: to design and assemble the elements of a "pre-feasibility package" based on the results of objective No. 1 and applied to one or more of three lesser developed areas (Latin America, Africa, and southeast Asia); and to disseminate, publicize, and demonstrate the "package" to potential investors in conferences and seminars.
Benefits expected from successfully achieving an operating facility include (a) new jobs for both skilled and unskilled workers, (b) production of forest products useful in developing local markets and competitive in world markets, (c) stimulation of ancillary industries, and (d) sizable savings in foreign currency exchange.
The planned research involves run-of-the-woods mixtures that simulate those found in the different climatic and geographic areas of the tropical forests. This approach was selected so that the information developed could be applied to any forest area of the tropics where even limited data on wood characteristics are available or readily gathered.
The basic premise for the research is that wood density is the most critical factor in determining the quality of product obtainable from a raw material supply. The question then becomes one of coping with unfavourable wood densities. Other factors such as silica content, extractives, and colour have been associated with certain processing and product-quality problems.
A second premise is that the natural tropical hardwoods are similar and information gathered in southeast Asia can be applied with good judgement to Africa and Latin America.
Information from the literature, from travel and mill visits by our staff, and from visitors to the Forest Products Laboratory reinforces the underlying premises and shows a need for this project. Present users and plans in progress selectively continue to exclude goodly numbers of wood species growing in the natural tropical forests. Such wood species are deemed "undesirable" for either product-quality or processing-problem reasons. This practice limits the development of a good and wisely applied silvicultural plan, leaving behind a forest of unwanted trees.
To face this problem, specified areas in three countries, representing three geographical areas, were selected for sampling of the wood resource. These were, in the order sampled, the Philippines (representing southeast Asia), Ghana (Africa), and Colombia (Latin America). The method of sampling for each location was essentially the same. From the literature, species with specified values for density, silica content, and extractives were designated as potential samples; thus the chosen density distribution mixtures could be simulated, low and high contents of silica and extractives would be available, and a range of colour from light to dark would be present. Some freedom of substitution was allowed where local conditions made it difficult to harvest a preferred species.
In the Philippines, 50 species were sampled, in Ghana, 22 and in Colombia, 18. The greater sampling in the Philippines was due to the scheduled broader range of effort for the first sample and the plan to use subsequent samples for spot verification of the first results.
The wood was airfreighted to the Forest Products Laboratory, where each species was debarked, sampled for wood analysis, chipped, and stored in a cold room for subsequent use. Three chip mixtures were made with the wood from each country. In one, the density distribution was uniform, in the second the higher densities were favoured, and in the third the median densities were dominant.
These mixtures were then the basis for exploratory tests in pulping, papermaking, and board production to establish procedures for pilot-scale runs on a variety of products - market pulp, newsprint, school paper, tissue, linerboard, corrugating medium, fibreboard, and particle board. They were also subjected to further treatment, based on the premise that eliminating the ultra-high-density chip material would in significant quality improvements in the products under test. Thus, the mixtures were subjected to fractionation on typical equipment for separation by specific gravity and on vibratory screens. The use of vibratory screens was based on the observation that our chipper produced smaller chips from the higher density woods.
The exploratory work showed that market-quality kraft pulps (bleached and unbleached) could be obtained from each of the three basic mixtures. There were, however, significant but probably unimportant differences in quality. It also appears that the wood from Ghana provided better quality pulp for all three mixes than was obtained from the Philippine wood. Data on Colombian woods are not complete. In general, the quality of tropical-hardwood bleached krafts would be equal to, but more likely superior to, present hardwood pulps produced in the United States and Scandinavia.
The three Philippine mixes appeared to pulp well by the neutral-sulphite semi-chemical process, but here the presence of the higher density woods definitely reduced the quality factors important to the production of corrugating medium. Thus far, we have not established whether cooking to lower yield or using higher alkali concentrations will permit the use of mixtures containing significant quantities of wood at densities above 0.66. With this question unresolved, neither the wood from Ghana nor Colombia has been evaluated by this process for possible use in corrugating medium.
Some efforts were directed at colour sorting of tropical hardwood chips by recognized optical procedures. While the system was reasonably successful, the rate at which chips could be separated was much too low to consider this as a commercial means to obtain light-coloured wood for the mechanical pulp required in newsprint. Thus, when newsprint is to be a manufactured forest product, log selection will be necessary to assure the light-coloured woods for the mechanical pulping process and thus avoid high bleaching costs.
Taking the chips from the three lightest-coloured woods, mechanical pulp was produced by the thermo-mechanical pulping process.
The resulting pulps were used in a variety of furnishes with topical-hardwood bleached kraft and commercial sulphite or sulphate softwood pulps to make newsprint on our 12-inch-wide experimental paper machine. Test data would indicate that commercial quality, strength and printability can be produced with furnishes approaching 100 percent tropical hardwoods. In all likelihood, a furnish of all tropical hardwoods could be run with only occasional additions of softwood pulps to alleviate minor operating problems.
Cultural papers - school and writing - were feasible using a furnish of 80 percent tropical-hardwood bleached kraft and 20 percent of a long-fibred sulphite or kraft. The use of some thermo-mechanical tropical-hardwood pulp as a substitute for the tropical-hardwood kraft appears possible, should such a pulp type be available.
Tissue grades (facial and toilet) and towelling are also possible products where high percentages of tropical-hardwood krafts are usable. Characteristics similar to commercial grades were found for furnishes containing as much as 80 percent tropical-hardwood kraft.
The work on linerboard and corrugating medium is still in process because of problems in the corrugating medium area. When these are resolved, the boards will be combined-and made into boxes for testing. We expect to be able to report favourably on the use of tropical hardwoods for producing these boards.
It was mentioned above that the chip mixtures were fractionated by specific gravity and screening procedures to eliminate some of the higher density wood. There procedures have had varying degrees of success, depending on the quantity of high-density wood in the mixture. Apparently, improvements in kraft pulp quality of 10 to 25 percent are possible. Thus, these procedures may be useful when it is necessary to improve competitive quality or to make a supergrade of hardwood kraft which could demand a higher price on the market. The reject material could be used as fuel for the process energy needed to produce pulp.
Wet- or dry-formed fibreboards made from the three tropical hardwood mixtures easily met the Voluntary Product Standards for regular hard-board. In addition, furniture core-stock and exterior-siding applications are possible with the respective resin formulations for such uses. In all cases, the fibreboard had excellent surface properties.
Although it is not a subject of research, a critical analysis has been undertaken of the literature relating to the environment and silviculture under a system which calls for more intensive utilization of the tropical forests. All of this is directed at applying the best technology to maintain the tropical forest as a renewable resource. Areas for research will be recommended.
In summary, forest products of satisfactory quality can be produced while using at least substantial quantities of the mixed secondary species from the tropical forests. If super-quality products are to be manufactured, the higher density woods can be separated by chip fractionation on screens and specific gravity separators. Any wood not acceptable for those forest products can be used as process fuel or for such other uses as chemicals and food.
Upon the completion of this research, an international meeting will present and discuss the new information, as well as other recent developments toward solving the technical problems restricting the use of the tropical hardwood resource. This meeting, the International Conference on Improved Utilization of Tropical Woods, will be held in Madison, Wisconsin, 21-26 May 1978.
Technical sessions in the preliminary plans include discussion of the resource, environment and silviculture, infrastructures, production of pulp, making of various paper grades, production of fibreboard and particle board, and finally application of the new technology. The agenda of the meeting appeared in the "World of Forestry," Unasylva, No. 116.
