In most agricultural crops, genetic variation can be sampled, collected and relatively easily stored and conserved in seed banks. Forest genetic resources are most commonly stored, in the long term, in living trees. Variations in forest cover, quality and composition thus have direct and decisive impacts on the extent and patterns of genetic variation in forest trees. Threats to the integrity of forest genetic resources include deforestation resulting from changes in land use, forest habitat destruction and alteration, inappropriate forest harvesting practices, and atmospheric pollution and climate fluctuations and change. In most regions of the world, these threats have increased in recent decades (FAO 1997a,b, 1999h; Ouédraogo 1997; Palmberg-Lerche and Hald 2000; Sigaud et al. 2000).
Genetically diversified local populations, which may possess valuable attributes, are further threatened by introduction of non-local forest germplasm for forest plantation establishment, which may lead to hybridization of local and introduced gene pools and to various degrees of loss of local adaptation in subsequent tree generations (Palmberg-Lerche 1999).
The aims of genetic management are to safeguard the evolutionary potential of ecosystems and species and to ensure the enhancement and sustainable utilization of the genetic variation available to meet present and future human needs. The specific objectives of genetic management will change over time, as environmental, economic and social conditions and requirements continually shift. Attention should therefore be given not only to those tree species, populations and genetic traits that are considered useful today, but also to those of potential future economic, social and environmental value (Eriksson et al. 1993; Namkoong 1986; Palmberg-Lerche 1999).
Since it is possible to conserve an ecosystem and still lose specific species, or to conserve a species and lose genetically distinct populations, genes or gene complexes that may be of future value, it is important to specify clearly, at the outset, the level or levels targeted. Decisions regarding strategies and methodologies will depend not only on the biological characteristics, genetic variation and variation patterns of a given species, but also on the degree of knowledge available regarding its silviculture and management; its present use, importance and uniqueness; perceived threats; and, quite decisively, the institutional capacities in the countries directly concerned, including infrastructure and availability of medium- and long-term funding (FAO 1993a; Kemp 1992; Kemp and Palmberg-Lerche 1994; Palmberg-Lerche 1994, 1999).
Conservation efforts must be accompanied by regular monitoring to ensure that progress is being achieved in reaching stated objectives, either through active management or through non-intervention. In regard to monitoring, it should be noted that there may be no single objective measure of biological diversity, only complementary measures appropriate for specified and, by necessity, restricted purposes (Williams et al. 1994). This further underlines the fundamental need to carefully specify objectives at the very outset of programmes.
The two main strategies for the conservation of genetic resources, in situ and ex situ conservation, complement one another. In situ conservation is the maintenance of a population in its natural or original habitat, within the community of which it forms a part. In practice, in situ conservation of forest genetic resources is carried out in forests experiencing varying degrees of human intervention, from strict protection to intensive management for specified goods and services.
Ex situ conservation includes conservation as seed, pollen or tissue, and conservation of genetic materials in live collections such as plantations, arboreta and clone banks, or in especially established ex situ conservation stands (FAO 1989, 1993).
