EXECUTIVE SUMMARY

The controlled exploitation of non-timber forest products holds great potential as a method for integrating the use and conservation of tropical forests. This report attempts to narrow the gap between the potential and the reality of this land-use practice. The main objective is to give a concise overview of the ecology, exploitation, and management of non-timber tropical forest plant resources in terms that can be easily understood by non-specialists.

The report is divided into three main sections. Section I summarizes the principal ecological characteristics of tropical plants that limit the nature and intensity of resource exploitation. Section II discusses the potential long-term ecological impacts resulting from the harvest of different plant parts. Section III presents a general strategy for managing non-timber plant resources on a sustained-yield basis. Within the context of the report, a sustainable system for exploiting non-timber resources is defined as one in which fruits, nuts, latexes, and other products can be harvested indefinitely from a limited area of forest with negligible impact on the species being exploited.

The report focuses exclusively on the ecological context of non-timber tropical forest products, with particular emphasis on the structure and dynamics of tree populations. It does not address the innumerable economic and social factors which are also important in determining the overall sustainability of forest resource exploitation.

THE ECOLOGY OF TROPICAL TREES AND FORESTS

1.   Tropical forests are characterized by a large number of tree species per unit area. Most of these species occur at densities of only one or two trees per hectare. Low density resources are difficult for collectors to locate, require long travel times, produce a low yield per unit area, and are extremely prone to over-harvesting.

2.   Tropical trees vary greatly in terms of the timing, duration and intensity of flowering and fruiting. Very few tropical forest species produce reliable fruit crops during a well-defined, predictable season each year.

3.   The great majority of tropical trees rely on animals to pollinate their flowers and disperse their seeds. Any serious program of commercial resource exploitation must include measures to conserve viable populations of these animals.

4.   There is a high probability that a seed will come in contact with an animal during the time between seed dispersal and seed germination. In most cases, this encounter proves fatal for the seed. In terms of total numbers, seed predation is one of the most severe sources of mortality during the life of a plant. Mortality is still extremely high following germination, and over 90% of the new seedlings may die before becoming established in the understoy. Only a very small fraction of these seedlings (less than 1 in 1,000,000 for some species) will ever make it to the canopy and produce fruit.

5.   The regeneration of many forest species is linked to the occurrence of canopy gaps. Based on the gap requirement and general shade tolerance of different species, three regeneration types of 'guilds" can be recognized: (1) early pioneer species, (2) late secondary species, and (3) primary species. The establishment, growth, reproduction, longevity, and management potential of the species in each group are markedly different.

6.   The population structure or size-class distribution of tropical trees can be described by three basic types. A Type I structure is displayed by populations that maintain a more or less constant rate of seedling establishment. A Type II structure is characteristic of populations that experience sporadic or irregular seedling establishment. The final type of population structure, Type III, reflects a species whose regeneration is severely limited for some reason. Although these three types correlate well with the regeneration guild of a species, a single species may exhibit any of these types depending on the environment and its current rate of seedling establishment.

IMPACT OF HARVESTING

7.   Almost any type of resource exploitation conducted in tropical forests will have an ecological impact. The exact magnitude of this impact depends on the floristic composition of the forest, the nature and intensity of harvesting, and the particular species or type of resource under exploitation.

8.   Given that the initial impact of resource extraction is determined largely by the specific type of resource or plant tissue harvested, the enormous variety of non-timber plant resources produced by tropical forests can be grouped into three major categories: (1) fruits and seeds, (2) plant exudates (e.g. latexes, gums and resins), and (3) vegetative structures (e.g. stems, leaves, roots, barks, and buds).

9.   Although unnecessary, many fruits and seeds are currently harvested by felling the tree. This practice has led to the serious depletion of several important fruit and oil seed-producing species. Even in the absence of destructive harvesting, the collection of commercial quantities of fruits and seeds can cause notable changes in the structure and dynamics of a tree population. These changes are typically precipitated by a reduction in seedling establishment due to over-harvesting. If uncontrolled, this process can result in the gradual extinction of the population under exploitation.

10.   When properly conducted, the extraction of plant exudates does not disturb the forest canopy, kill the exploited tree, or remove its seeds from the site. There are, however, several examples of exudate-producing trees that are harvested destructively, and even the non-destructive tapping of rubber can cause a reduction in the growth and reproduction of wild Hevea trees.

11.   The harvest of vegetative structures produces one of two different impacts. The plant species will either be killed in the process, or, in a limited number of cases, it will survive and later regenerate the vegetative structure removed. Rattan is a well-known example of the former scenario, and uncontrolled harvesting is rapidly depleting this non-timber resource in Southeast Asia. Leaves and buds are examples of vegetative structures that regenerate after harvesting.

STEPS TOWARD SUSTAINABILITY

12.   An overall strategy for managing non-timber tropical plant resources on a sustained-yield basis is presented. The procedures described are sufficiently general that they can be applied to any class of non-timber resource, or to a mixture of different resources, on a scale from 100 to 100,000 hectares. They can be applied in forests that have already been heavily exploited for non-timber resources, as well as in more pristine, undisturbed habitats. These guidelines, however, do not comprise a single management technology or "package" that can be blindly applied without modification. Instead, the basic concept is to provide a constant flow of information about the ecological response of a species to varying degrees of exploitation. Sustainability is achieved through a continual process of adjustment in which any change in seedling establishment or population structure results in a corresponding change in harvest level.

13.   The complete process of sustainable exploitation is composed of six basic operations or steps: (1) species selection, (2) forest inventory, (3) yield studies, (4) regeneration surveys, (5) harvest assessments and (6) harvest adjustments. The actual sequence of operations is not fixed and can be adapted to a variety of different situations.

14.   Species selection will be based largely on economic and social criteria. A third criterion that should also be considered is the overall potential of the resource to be managed on a sustained-yield basis. Although the fact is frequently overlooked, some forest species are inherently better able to withstand the continual perturbations caused by resource extraction than others. Important ecological factors to consider include the life cycle characteristics of the species (e.g. phenology of flowering and fruiting, pollination, and seed dispersal), the type of resource produced, its abundance in the forest, and the size-class distribution of natural populations.

15.   Density and size-class structure data are the most fundamental pieces of information required for management. The collection of these data requires a quantitative forest inventory. The inventory should provide an estimate of the total number of harvestable trees per hectare in different forest types and should document the existing size-class distribution of adult trees. These data will be used to construct a size- class histogram for the species being harvested. It is strongly recommended that a professional forester or inventory specialist be involved in the planning and execution of this fieldwork.

16.   Yield studies are conducted to estimate the total quantity of resource produced by trees of varying size. Just as foresters use growth data to avoid cutting timber faster than it is produced in the forest, the sustained- yield management of non-timber resources also requires information about the productive capacity of the species being exploited. Probably the easiest way to obtain production data is to train local collectors to weigh, count, or measure the quantity of resource produced by different sample trees during harvest season. These studies should be repeated every few years using the same group of sample plants to monitor the variation in yield over time.

17.   Periodic regeneration surveys are used to quantify the initial density of seedlings and saplings in the populations being exploited, and to monitor the way in which these densities fluctuate in response to differing harvest levels. The results from these surveys are divided into height classes and then added to the size-class histograms constructed from the inventory results to provide a complete picture of population structure from seedlings to large adult trees. Repeating these surveys every five years is probably sufficient for most species.

18.   Harvest assessments are visual appraisals of the behavior and condition of adult trees that are conducted concurrently with harvest activities. In many cases, these quick assessments can detect a problem with reproduction or growth before it becomes serious enough to actually reduce the rate of seedling establishment.

19.   The seedling and sapling densities recorded in the original regeneration survey are used as the threshold values by which sustainability is measured. As long as densities remain above these values, and no major problems are detected in the harvest assessments, there is a high probability that the current level of exploitation can be sustained. If seedling or sapling densities are found to drop below this value, however, immediate steps should be taken to reduce the intensity of harvest. Two different procedures are described to make these harvest adjustments. The first method regulates the number or size of the plants being exploited. The second method limits the total area from which the resource can be harvested. For populations that have never been exploited before, a good first approximation is to extract no more than 80% of the total harvestable yield during the first collection cycle.

20.   The six-step management strategy provides a simple and effective method for achieving a sustainable harvest of most non-timber forest products. In some cases, however, a more intensive form of management may be required. If, for example, seedling densities continue to drop in spite of drastic harvest reductions, or productivity declines, or trees start to die, some form of remedial treatment should be initiated as soon as possible.

Potential courses of action include enrichment planting, selective weeding, and the cutting and removal of woody vines.

CONCLUSIONS

21.   There are convincing ecological reasons to implement the management strategies outlined in this report. If practiced on a sustainable basis, the exploitation of non-timber forest products provides a unique way to use species-rich tropical forest for profit and still conserve most of the biological diversity and ecosystem functions of the forest. No other form of land-use practiced in the tropics has the potential to do this.

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