R.H. Kemp
Ronald H. Kemp is an independent consultant who specializes in forest management and forest genetic resources. He is based in Surrey, England. This article is based on a larger work, Conservation of the genetic resources of tropical trees in production forests, currently in preparation for the Forest Resources Division of FAO.
The biological diversity of tropical forests constitutes a unique national and international asset. As human populations continue to increase, setting aside large areas purely to preserve biodiversity becomes more and more difficult. At the same time, however, the conservation of genetic resources is fundamental to the sustainable management of the forest ecosystem in which they occur. In situ conservation of forest genetic resources, and particularly those of trees which are dominant in determining the unique genetic potential of the system, should be reinforced in the management of production forests.
Forest genetic resources are a national asset and their use and conservation depend on and policies
Genetic diversity is a product not only of the number of species present in a given area but of successional change, from the colonization of gaps by pioneer species to the mature climax forest. Depending on the exact systems of management, and the degree of understanding of the forest dynamics on which they are based, genetic diversity and specific genetic resources may be enhanced or reduced in specific areas of forest and over specific periods of time. A lack of active management - for example, through the complete exclusion of human intervention - may at times reduce genetic diversity, although in certain circumstances it may be needed to conserve specific genetic resources. The most species-rich areas are likely to be those including secondary forest in various stages of recovery.
To a large extent, each forest area is unique in terms of its genetic resources and, consequently, in terms of its potential contribution to the achievement of national forest production and genetic conservation objectives, as determined by prevailing ecological, social and economic needs. It is neither possible nor desirable to prescribe equal priority and intensity of in situ conservation in all production forests. However, all management plans should include provisions for the protection of site conditions, seed trees, seedling regeneration and advance growth of desirable species according to management and silvicultural prescriptions.
Notwithstanding the unique character of each forest area, genetic resources are a national asset and are therefore dependent on clear national policies for their use and conservation. Actual conservation must be carried out at the level of the individual forest, whether it be privately, communally or government controlled. Nevertheless, to have more than very limited chances of meaningful success, genetic conservation must be an integral part of overall national development policies, not only relating to forest and land use but embracing forest industry, trade and linkages with other sectors. It is national governments who hold the power to formulate the necessary policies in land and resource use for sustainable forest management and conservation of the nation's genetic resources.
The conservation of a wide diversity of species and variation in natural forests is dependent on maintaining essential functional components of the ecosystem. These often involve a range of complex interactions; for example, between tree species and their animal pollinators, seed dispersers and so forth. Therefore, although the objective may be to conserve particular target species and populations, in practice this is likely to involve conserving whole communities, at least until it is possible to have a more complete understanding of ecosystem dynamics (Gilbert, 1980; Terborgh, 1986; Whitmore, 1990).
The diversity found within species viewed as having current or perceived future socio-economic value must be the main target for in situ conservation, which should aim to maintain viable breeding populations and a broad genetic base. Depending on the pattern of distribution of such variation through the stand, as a result of the nature of the species' breeding and dispersal systems, highly valuable genetic resources at the intraspecific level may be lost even if the population as a whole survives.
At the level of the gene, differences - for example, in resistance to insect pests or severe environmental stress - could be the basis of valuable traits of great potential value for future use. It is therefore essential that all levels of genetic diversity be included in the objectives and the activities of a conservation programme (Namkoong, 1990), although it is not always necessary to attempt the conservation of all levels of genetic diversity in all areas. While some forest reserves will be devoted to ecosystem conservation, others may be dedicated to conserve intraspecies variation in a network of conservation areas containing selected "target" species or subspecific populations. For example, if done with a full understanding of the ecosystem's dynamics and the effect on its long-term functioning, the extreme refinement of a selected forest area to favour one or a few species may be an acceptable means of conserving the principal species' genetic resources, albeit at the expense of the broader genetic diversity of this area.
In the absence of information on the nature and distribution of genetic variation of almost all tree species in tropical forest areas, the safest practicable conservation strategy must be to conserve a wide selection of provenances from the natural geographical and ecological range. It is also desirable to protect their integrity against genetic pollution by another provenance of the species.
While a fully protected system of nature reserves may include a partial range of a species, the effective conservation of the gene pool requires a much wider range of populations representing possible genetic differences which, at present, can only be hypothesized according to their geographical or ecological situations (Franker, 1970). This is likely to require a number of conservation areas scattered over the entire natural range of a species, with most of these areas probably having to serve multiple objectives, including timber production.
Logging and genetic diversity
Selective logging in mixed tropical forests as part of an overall forest management plan might, in theory, be managed to maintain an optimal balance between the various stages of ecological succession, thus allowing for maximum genetic diversity and the conservation of genetic resources of both pioneer and climax species. This might be achieved by clear-cutting at very long intervals to allow each felled area in turn to revert to its mature condition; by the careful opening of small gaps by the removal of individual trees; or through various possible intermediate patterns and levels of harvesting. However, over-frequent selective harvesting, even of light intensity, may adversely affect the breeding populations of the slower-growing species if the number and distribution of mature reproductive individuals which are present before the subsequent felling cycle are severely altered.
The importance of leaving seed trees of good phenotypic quality at the time of logging, particularly if regeneration sampling has revealed low levels of established seedlings and advance growth of the desirable species, is a further example of common production and genetic conservation objectives. In practice, however, this vital aspect is commonly overlooked or overridden because of pressures for maximum harvest yield and profit. The retention of large seed-bearers after the main logging operation does present some disadvantages in subsequent management of the stand if they are so numerous as to cause depressive shade or competition, or if they are subsequently harvested, causing extraction damage to the regenerating forest. However, the effective production losses are slight in comparison to the dangers of the population's progressive genetic deterioration resulting from its reliance on the small, probably less vigorous and less desirable, residual individuals for regeneration.
The seedlings of climax species are particularly vulnerable to damage by heavy logging tractors, as their successful regeneration is a result of long periods under the forest canopy rather than their rapid colonization of gaps or their sprouting from dormant seed banks in the soil. This compounds the adverse impact that extensive and sudden canopy opening has on such species. Since it is the heavy seeded climax species which are most dependent on animal seed dispersal, the extent to which logging disrupts animal populations may also affect these timber species. Studies indicate that quite small areas of forest within or adjoining logging concessions may be critically important to the survival of keystone animal species (Johns, 1989) and, consequently, to the long-term sustainability of the whole area in question. Stock mapping, timber marking, regeneration surveys and operator training, linked to the careful planning of road construction and logging operations, could be designed to conserve target species and populations.
In complex forest formations fire can severely reduce species' richness and genetic resources
An often inadvertent but severe effect of human intervention that may follow logging is increased susceptibility to fire.
While some forest formations are adapted to survive periodic burning, the adverse impact of fire in other more complex formations can severely reduce species' richness and genetic resources. In extreme cases, whole populations of a given area, including those in the process of regeneration, may be lost through fire after the felling of adult trees.
Where market demand is very selective, extraction may concentrate exclusively on the best individual trees (phenotypes). In the absence of subsequent silvicultural treatments to favour regeneration and growth of desirable species and individuals, this may lead to a progressive deterioration in the stand's genetic quality. However, even the much narrower range of genetic diversity that will result from repeated extensive harvesting and refinements of the forest is likely to be greater than if the same area were converted into forest plantations, and will certainly be greater than it would be under most alternative forms of land use. Where a broader range of species is utilized, there may be the opportunity for increased reinvestment in sustainable management, including the incorporation of silvicultural and genetic considerations into integrated forest management plans.
Nevertheless, with adequate control based on a sufficient understanding of the ecological processes involved, logging and timber extraction as part of overall management plans can be used to assist the conservation of a wide spectrum of the principal tree species' genetic resources. It may be difficult or, in some cases, impossible to combine a range of different management objectives for a limited area of forest while maintaining the same intensity of timber harvest. On the other hand, canopy opening, population refinement and the creation of different working circles within the same forest may be used to maintain a mosaic of different ecological stages or conditions.
In some cases working circles may overlap, while in others they must be kept geographically separate. Such zonation is also compatible with the development of "buffer zones" around the forest and the designation of "core zones" for stricter protection and a more rigorous emphasis on conservation. Clear objectives and priorities must be set for each zone, from the "core", where the conservation of biodiversity may be paramount, to the outer zones, where the production of wood and non-wood forest products may be the highest priority. The close involvement of local communities and due consideration for the resource's sustainability are essential. Both the efficiency with which this is achieved and the security assured against accidental loss of substantial elements of the gene pool will be dependent on the management of a network of conservation sites in production forests and fully protected areas containing the natural range of the principal species.
Forest inventory
The scientific basis for the conservation of species and their genetic resources depends on the study and interpretation of taxonomic information, relating to genetically determined differences and affinities among species, their patterns of natural distribution and the ecological basis for their occurrence. These three interdependent sets of data are inadequate and in many cases non-existent. Very often, the only data available are the result of traditional forest inventories, concerned primarily or exclusively with stocks of harvestable timber. Little regard has been paid to the actual composition or condition of forests.
Inadequate information on the species composition of the forest is one of the main problems confronting natural forest management, both in terms of the forest's full economic value and its regeneration potential (Wyatt-Smith, 1987). Given the relatively high cost of inventory activities concerning actual access to and work in the forest, the additional cost of collecting a wider range of data in the course of the timber survey is low. The key to an efficient and cost-effective inventory is to ensure an appropriate range of botanical, ecological and sociological expertise at the planning stage.
Non-timber forest products (NTFPs) often represent the highest value of the forest in the eyes of local people and am therefore an important factor in forest conservation, including that of genetic diversity. Insofar as the conservation of a wide range of tropical moist forest genetic resources is dependent on management systems that mimic natural ecological conditions and processes rather than drastically altering forest conditions, revenue derived from managed non-consumptive harvesting of NTFPs may be: important in funding conservation activities. However, it will be essential consider NTFPs in inventory exercises and to specify precise objectives in the management of each area of forest.
National data centres
Forest management for in situ conservation of genetic resources requires much of the same basic data on ecology and autecology (the relationship between individual organisms and the environment as a whole) that underlies silviculture in the natural forest, but with a greater emphasis on breeding biology and genetic structure. A variety of information sources, ranging from herbarium sheets to expedition records and academic theses, could contribute data needed on forest composition, species distribution, the phenology of flowering and fruiting and so forth.
Modern computerized systems can be used to store and facilitate the interpretation of data and to guide the efficient collection of additional information to fill the most important gaps (Jenkins, 1988). The use of Geographic Information Systems (GIS) can be a powerful aid in the definition and interpretation of species' distribution patterns in relation to environmental variables and vegetation types. Similarly, computer systems for handling taxonomic data have improved the accessibility and usefulness of information on genetic diversity with respect to both taxonomic groups and geographical areas.
National strategies
Effective forest genetic conservation requires coordinated efforts by the entire forestry sector- including industry and trade as well as by groups outside the forestry sector. Existing laws and regulations may need to be revised and a coherent system of incentives for sustainable forest management at all levels as well as appropriate international market conditions and investment policies (fair trading practices, support for local processing, marketing assistance and an increase in the value of products for the country of origin, etc.) will be needed to ensure that greater attention is paid to genetic conservation objectives in production forests. These incentives must be formed at the national level but are likely to require international assistance.
An urgent task is the determination of priority (target) species, populations, areas and actions for the conservation of forest genetic resources in individual countries. This must take account of possible ex situ as well as in situ conservation, within a coherent programme and in accordance with the national policies and biological possibilities regarding each species. The formulation of a national strategy for the conservation of forest genetic resources is a critical element in ensuring the best use of land and other resources devoted to production and protection, and in ensuring that opportunities for regional cooperation and international assistance are taken.
Forest inventories need to concentrate on more than commercially valuable timber
The formulation of such a national strategy may be carried out best by the Forestry Department but the need to secure strong intersectoral cooperation and high-level policy reviews calls for close involvement with, if not actually within, central government structures. The definition of appropriate institutional structures to guide and coordinate subsequent action will be an essential element of the process.
Concern for the tropical forests is certain to continue and to deepen as the resource is further reduced. The scale of action required to maximize the sustainable productivity of remaining areas of natural forest and to conserve the diminishing genetic diversity demands the most efficient use of the limited resources and time available.
In all aspects of forest management and genetic conservation, the failure to comply with established prescriptions and conditions has been a frequent cause of damage to growing stock, and particularly its capacity for regeneration. Close monitoring of operations, both to judge their conformity with prescriptions and to assess their effect relative to the declared objectives, is in the common interest of both sustainable production and genetic resource conservation. As stated earlier, it is neither possible nor desirable to attempt to impose genetic conservation measures with equal priority and stringency in all production forests. To do so could weaken the support for the concept of conservation among forest managers and invite widespread disregard for the application of such measures.
In situ conservation of Baikiaea plurijuga in Zambia
Reproductive biology, embracing studies of pollination, seed dispersal and predation and the dynamics of regeneration banks of seed, seedlings and saplings - which are clearly important in genetic resource conservation has also been identified as a necessary field of knowledge for the forest manager (Palmer, 1989). The number of species requiring such study, even in a single forest, is very large, while the skilled human resources are very limited. An important task, therefore, will be the prioritization and coordination of research, without which the limited scientific expertise may be wasted or inefficiently used. This has been observed particularly in the fields of reproductive biology and genetics of tropical trees in relation to their conservation and management (Bawa and Krugman, 1991).
Studies of the effects of disturbance on the forest and the response of the principal economic species at various stages of their life cycle are also important for management and genetic conservation objectives. There is need and scope for a wide range of biological interests in this field and for varying degrees of expertise and technological sophistication in the methodologies used.
Too often, however, ecological and autecological studies have lacked direct relevance to forest management by failing to examine the comparative situations in both logged and unlogged forest. The same main lines of research needed and, at least at a regional level, the principal species requiring study are likely to be common to many countries.
Advances in information technology are already transforming the possibilities to handle and interpret complex arrays of data for the better understanding of functional relationships in forest management. In the future, a more appropriate response to the management of diversity will be greater choice of management. This may be achieved in venous ways, including multiple use of the same area of forest, either simultaneously or in successional stages; separate management by compartments or working circles; and integrated and diversified management of an entire national forest estate, embracing both production forests and protected area networks.
Finally, although the management of forest resources, and particularly their genetic diversity, must be undertaken at the local level within the context of national plans, there is ample scope for international cooperation. The international convention on biological diversity, currently being negotiated, is an important step in this direction.
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