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Sometimes the word is "weed": A critical look at lesser-known species

James S. Bethel

James S. Bethel is Dean Emeritus of the College of Forest Resources, University of Washington, Seattle, USA, and a well-known international forestry consultant.

Although much recent attention has focused on the problem of finding markets for products made from "lesser-known" or "secondary" species in the tropics, the simple fact remains - according to James S. Bethel - that many of these species must be regarded as "weeds". Forestry, unlike agriculture, has been slow in switching from "exploitation" to "management". Only occasionally, Bethel argues, will research and investment in lesser-known species bear results. Attention would therefore be better devoted to the conversion of existing mixed stands of tropical forest to managed forests.

The literature on forestry in the developing countries is replete with references to the "lesser-known" or "secondary" species problem. However, this is not really a problem unique to developing countries at all. It is and has been a phenomenon wherever "forest exploitation" as a method of forest use occurs. It is generally not a problem associated with intensive forest management. "Forest exploitation" involves the search for merchantable species and specimens from among the trees that happen to occur in natural or secondary forests. Forest management, on the other hand, involves growing trees that are known to be merchantable.

TEAK PLANTATION IN HONDURAS - favouring a single species over many

Forest exploitation vs. forest management

The utilization of forests as sources of renewable industrial materials, including fuel, has generally followed a straightforward developmental progression from exploitation to management. The first effort typically involves exploiting a natural or secondary forest to extract usable components of the forest biomass; converting these components to products for which there is a demand; and then selling them in the market-place. For a particular exploitation forest this process may be repeated at various intervals of time, either to exploit components of the forest biomass not merchantable at the time of the first exploitation or perhaps to harvest new trees that have replenished the growing stock through natural regeneration following the first exploitation.

This is an extension of the practice of individual forest dwellers, who search in the natural forest for trees that are appropriate for fuel, tools or shelter. It has its counterpart in agriculture in forest dwellers' search in the forests and fields for edible components of the biota in the form of fruits, nuts, fungi, honey and wild game of all kinds. Some naturally occurring forests are rich in components that are preferred by humans for food to eat, for wood to provide shelter and for fuel to heat homes and cook meals. Other naturally occurring forests are poor in their yield of these preferred species. The richness of the biota in preferred components is a function not necessarily of the productivity of the forest but rather of the match between naturally occurring biota and human preferences for food and fibre.

SELECTIVE TREE-POISONING IN BRAZIL - to encourage growth of commercial species

A forest poor in its yield of preferred components can be a difficult place to live. The forest dwellers may have to travel great distances to find their preferred plants and animals; and, having found them, to transport them great distances back to their homes for consumption. One response of the forest dweller to this problem is to use less-preferable but still useful components of the forest for food, fuel and fibre. Such a response represents a trade-off between the work essential to obtain preferred materials and a willingness to accept less desirable materials. But even when less-preferred components of the biota are used, there are typically large numbers of plants and animals that make no contribution to the supply of food, fuel and fibre and that occupy space in the forest that might otherwise be filled by preferred components. This is not to say that these plants are not useful - it is simply that they are not used.

In every case the development of a new product from a previously unused or underused species has been as much a function of proximity to market and economic feasibility as a matter of wood properties.

In the agricultural sector, development has often taken the form of commitment of land specifically to food-crop production. In effect, those plants that are either useless or less preferred as food - weeds - are replaced on that land by plants that are high on society's preference scale for food. The food may, of course, represent primary or secondary production; the farmers growing the food typically provide food not only for their own needs but also for market. Hence, their farming must be economically feasible.

In the case of some exploitable forests, the proportion of the tree biomass in demand for industrial materials is large and the harvesting and manufacturing operations can be efficient and represent a cost-effective basis for competing with other uses for productive land. But in other exploitable forests, the proportion of the tree biomass that is in demand for industrial material and fuel is very small. In these cases, where the value of the forest-material output is small in comparison with the value of the output from other land uses, the forest land is likely to be converted to non-forest use as population density intensifies the competition among various land uses for productive land.

The natural forests of the humid tropics are among those that have traditionally been low in production of materials that are in demand in the market-place. This has contributed significantly to the tropical deforestation problem that has achieved so much prominence in the last five years. Clearly, however, the opportunities for renewable industrial-materials production are not limited to what can be gleaned from natural forests.

When exploitative use of the natural forests does not provide enough products to meet the demands of society, it may become both feasible and desirable to grow a crop of trees in a managed forest to serve as raw material for a forest-utilization system responsive to social preference. This is the forestry counterpart of agricultural development through farming. As in the case of agriculture, it may result in the growing of trees that produce materials that are in demand and the exclusion of trees that do not produce market-preferred materials - that is, weeds.

It should be re-emphasized that the roles of the exploitation forest and of the managed forest as an industrial-material supply base in a forest-utilization system are quite different. In an exploitation forest, the challenge is to find among the naturally occurring trees some that can be converted to merchantable products. In a managed forest, the task of management is to grow those trees that are needed to supply industry with its raw-material requirements, so that it can satisfy society's demands for renewable materials. One is a search-and-find operation while the other is a tree-crop-growing operation.

Exploitation forestry has proved to be a much more durable enterprise than has exploitation agriculture. Societies that long ago developed their agriculture to the point of producing preferred plant species to meet their needs for food have continued to depend upon exploitation forestry to meet their needs for wood. When the quantity of preferred trees in the natural or secondary forest represents a small part of the tree biomass, there is always a temptation to augment the timber production by attempting to market less-preferred species. This is often pursued using the rationale that if we just knew enough about these species, we could convert them to useful products and thus eliminate the problem. The result is that a great deal of time and effort has been devoted to research designed to find uses for the non-utilized species. Unfortunately, these efforts have not always been highly successful.

Secondary species: The problems

In the United States in the two decades following the Second World War, great efforts were made to find uses for what were termed "low-quality hardwoods". Almost every forestry experiment station had a project designed to seek uses for such species. Some of these efforts were combined in large cooperative ventures among federal and state governments and universities; examples were the "hickory task force" and the "beech task force". While these research efforts did indeed result in the development of products that could be manufactured - notably pallet stock - these less utilized species, for the most part, were not converted into highly marketable commodities at the levels of their availability.

It is important to recognize that merely because a tree species can be converted into a merchantable product at some level, it does not mean that an indefinite quantity of it can be sold. The dandelion plant, for example, is used by some people in green salads, by others as a green vegetable and by others in the production of a palatable wine. But the quantity of this plant that can be sold for these food products is so minute compared with the total number of dandelion plants in the area of its natural range that for all practical purposes it should be - and is - considered a weed and thus eliminated from farm fields. The same situation prevails for some tree species.

The major problem in this domain is that all too frequently there is confusion between species utility and species merchantability. There are very few trees that are literally not useful. All trees will burn if they are dry enough, and most trees can in fact be fashioned into several kinds of useful products. The problem is to convert them into useful products that are acceptable in the market and that can be profitably sold at prices competitive with alternative products in the same market.

As previously noted, not all natural forests are equally vulnerable to the lesser-known- or secondary-species problem. Some natural forests are essentially even-aged, single-species forests. If the species making up such a forest is one that is in great demand for conversion to forest products, there is likely to be no significant secondary-species problem. The Douglas fir forests of western North America are one example. At the other extreme of the utilization spectrum are the variable-aged, mixed-species hardwood forests common to most forested areas of the world, especially in the tropics. Here the number of useful trees, at any time, may be very small indeed. There are usually some very fine materials components in these forests, but there are many trees representing species that are not in demand and simply cannot be sold at a price that will recover the cost of extraction.

The forests of the humid tropics exhibit the "lesser-known-species problem" more than any other forests in the world. This is because they have more non-merchantable species. In his analysis of forests as a source of renewable materials, made for the US National Commission on Materials Policy, Cliff (1973) said:

Characteristically, tropical rain forests are a mixture of large numbers of species. As many as several hundred per hectare have been reported. Most of these species are not used in commerce. Their wood properties vary widely and have not been well defined in terms that can be used in developing markets for them.

Discussing tropical forest ecosystems, Catinot (1972) noted in an address to the World Forestry Congress:

As knowledge of these ecosystems advances, a certain disappointment is felt, so complicated is their study and so modest their wood production; 400 cubic meters per hectare of biological production and 6 to 50 cubic meters per hectare of economic production.

Examining the forests of the humid tropics from an ecological vantage point, Golley (1975) has noted:

A large biomass is generally characteristic of tropical forests. The quantities of wood especially are large in tropical forests and average about 300 tons per hectare compared with about 150 tons per hectare for temperate forests.

These statements indicate the origins of the lesser-known-species problem in the humid tropics. While they all point to the large biomass typical of the forests of the humid tropics, it must be said that from a standpoint of industrial-material supply this is relatively unimportant. The important question is how much of this biomass represents trees and parts of trees of preferred species that can be manufactured into products that can be profitably marketed. Johnson (1975) highlights this problem:

On the west coast of North America early loggers commonly found Douglas-fir with over 2000 cubic meters per hectare; yet in the East Kalimantan we log less than 60 cubic meters from the average hectare. Even clear-cutting and full utilization of all trees 15 centimeters diameter and above would only double this value.

It should be noted that the forests of Kalimantan that Johnson referred to are dipterocarp forests, which, of all of the forests of the humid tropics, are, in terms of industrial materials, among the most productive. The author (1982) has studied the utilization potential of some humid tropical forests in Southeast Asia and Latin America and found yields varying from 4 to 48 cubic metres per hectare under the most optimistic utilization assumptions. By today's utilization standards, most of the trees in these humid tropical forests are, from an industrial-materials standpoint, clearly weeds.

By today's utilization standards, most of the trees in the humid tropics are, from an industrial-materials standpoint, clearly weeds.

One reason that many of the so-called secondary species are under-utilized is that the fraction of the total stem biomass that can be sold in the market-place is very small. The work required in harvesting, transporting and manufacturing may be rewarded with a very small yield of merchantable product. When timber is harvested from exploitation forests, the final yield of product from a tree is often as low as 10 to 20 percent and typically averages no more than 30 percent. In managed forests grown for industrial-materials production, trees are typically selected for the potential of much higher yields.

LOGS READY FOR SAWMILLING - traditional species are easier to market

The managed forest

If the forests of the humid tropics are to contribute significantly to the production of industrial wood in the countries where they occupy large areas of land, then it will be necessary to foster the production of preferred species and to eliminate weeds. It is instructive, in this context, to examine some of the reasons for forestry's long delay, in comparison with agriculture, in moving from exploitation to management. Among the reasons are the following:

· In contrast with agriculture, the production of a merchantable crop of trees from bare land to harvest size often takes a long time. This long lead time, with its associated requirement for market forecasts, sometimes discourages investment in the development of managed forests.

· The forestry doctrine of multiple use, often incorporated into national laws, has too frequently been interpreted to mean all uses - with equal attention paid to all these various uses. This view of multiple use often results in the maintenance of natural-forest mixtures and the retention of species that from an industrial-materials standpoint would be regarded as weeds.

· Forest inventory practices often include utilization standards that are totally unrealistic in terms of commercial feasibility. Tree species are counted and measured as merchantable forest components just because one or two mills may be willing to process an occasional tree. This is the dandelion syndrome applied to forestry.

· Too often there is a failure to recognize that most tree species in a mixed-species tropical-hardwood forest occur so infrequently, intermittently and irregularly in a harvesting operation that it is virtually impossible to develop around them a viable product-manufacturing operation. This is particularly serious when log storage for any appreciable time is as hazardous as it is in the humid tropics.

· There is too much wishful thinking on the prospects for developing instant new markets for previously unknown and unmerchantable species. Local patterns of wood consumption typically change slowly, yet it is in domestic markets that new species and products can most easily be developed. It takes a long time and the expenditure of much effort and money to introduce new species to international markets. Such factors as product-quality control and the quantity and reliability of supply may be at least as important to market development as the properties of the wood.

· There are often too many unrealistic expectations about the impact of new manufacturing technology on the utilization of currently unmerchantable woods. New manufacturing technology is typically developed to improve the use and merchantability of woods that are currently well known and accepted in the market. Manufacturing processes that are indiscriminate with respect to species are usually also those that require very large capital investments - something that is sometimes not readily available in developing countries. Even when it is technically feasible for a manufacturing process to be indiscriminate with respect to species, it may be economically advantageous to supply it with a uniform raw material.

A search for new uses for non-utilized and under-utilized species is not an inappropriate objective of research. Some great successes have emerged from just such research. The development of new pulping processes, for instance, converted western hemlock from a weed that was left in the forest as a logging residue to a very valuable species. The development of waferboard and oriented fibre-board has opened up a bright future for the aspen, which has for so long been considered a weed in the forests of the US lake states. Research on coconut wood shows promise of making the stem of the coconut palm a valuable materials-supply source.

There are other, similar examples, but in every case the development of a new product from a previously unused or underused species has been as much a function of proximity to market and economic feasibility as a matter of wood properties. The danger in placing too much emphasis upon the development of new products from currently unused or underused secondary species is that it provides an excuse for allowing productive forest land to be occupied by weeds on the remote chance that tomorrow they will not be weeds.

Given the fact that some of the unused and underused species do, in fact, sometimes become useful raw materials, it is clearly unwise to eliminate them entirely. They should be represented in gene pools where they can be studied and propagated when they are found to be merchantable. But it is clearly not good use of productive forest land dedicated to materials supply to permit it to be occupied by weeds.

The discussion of the "lesser-known-species problem" has been focused upon the recovery of industrial materials from lands whose primary role is to provide such materials. In every forested country there are lands in the forest sector whose forestry role may be quite different. These may include forests that serve primarily as parks or wildlife refuges. They may include forests dedicated primarily to the protection of the watersheds of reservoirs. Sometimes forests in national-government, village or tribal custody are reserved for free or customary use by the forest dwellers for various goods and services, including industrial wood products. For such forest lands, efficiency in the production of forest products may be unimportant. Variety in the biota may be a real asset here, as the forests can provide for a broad spectrum of multiple use. Experimentation with secondary species on a cottage-industry basis may be highly appropriate, but where there is a need for serious production of forest-based industry materials to meet domestic need or to improve upon the national GNP through product export or import substitution, then betting heavily on the development of significant markets for currently unused or underused species may be a poor gamble. In such circumstances these so-called secondary species must simply be regarded as weeds.


BETHEL, J.S. 1982

Processes of optimising and diversifying the materials output from a forest. In Proceedings International Forestry Seminar, 1980. Kuala Lumpur, Universiti Pertanian Malaysia.

CATINOT, R. 1972

Biological and economic opportunities and limitations to the manipulation of the tropical forest ecosystem. Address to the 7th World Forestry Congress, Buenos Aires.

CLIFF, E.P. 1973

Timber, the renewable material. Report prepared for the National Commission on Materials Policy Washington, D.C.

GOLLEY, F.B. 1975

Productivity and mineral cycling in tropical forests. In Productivity of world ecosystems. Washington. D.C., National Academy of Sciences. p. 106-115.

JOHNSON, N.E. 1975

Biological opportunities and risks associated with fast-growing plantations in the tropics. Unpublished paper prepared for the Technical Conference on the Tropical Moist Forest, originally scheduled for Rome., Sept. 1975.

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