Conserving forest biodiversity

The complexity of forest ecosystems; the dominant role of tree species in them; the environmental and economic value of forests and trees, and the poor conservation status of most tree populations ex situ, have all led to forest trees being regarded as a paradigm of the need for [in situ] conservation. The provisions of the [Convention on Biological Diversity] entail a comprehensive approach to [in situ] conservation going beyond simply creating protected areas. Effective [in situ] conservation (Article 8) demands that both ecosystem functions and processes, and intra-specific population genetic processes, are maintained in a network of sites which are comprehensive and representative in terms of all levels of genetic organisation.

Conservation strategies have envisaged a reserve system of protected areas, the ultimate expression and focus of [in situ] conservation, buffered by land uses which operate in support of [in situ] conservation objectives. Reserve models based on population genetic principles, using various measures of population viability, imply that very large areas may be required for the conservation [in situ] of many forest tree and animal species. For example, some tree species occur at densities of less than one per hectare, or have reproductive systems which promote mating between geographically disparate individuals, implying minimum area estimates for viable populations in the hundreds of hectares; estimates on the same basis for predatory forest animal species can be in the millions of hectares. These ideal reserve models demonstrate two major characteristics of for in situ conservation of forest biological diversity. The first relates to the location of reserves, and the second to their size.

The provisions of the Convention however entail a more holistic, ecosystem approach to protected areas than has generally been the case. The history of establishment of protected areas, typically on sites less favoured for agriculture or production forestry, reveals (i) that choice of sites has been made on criteria other than the maintenance of biodiversity, and (ii) that national reserve systems almost invariably represent a biased and inadequate sample of ecosystems and populations, with an over-representation of uplands and slopes, sites of lower fertility, and stands of lesser economic value. Similarly, because few have been established or managed according to population genetic principles, they do not necessarily comprise viable populations of forest species.

While ideal reserve models emphasise the importance of large contiguous areas for in situ conservation, they also demonstrate that systems of fully protected areas are insufficient, by themselves, for the conservation of forest biological diversity. The mobility of many forest animal species, the extensive geographic distribution of most tree species, the reproductive biology of tree species and the high levels of gene flow between populations, and the large areas associated with minimum viable populations of many tree and animal species, emphasise the essential contribution of forests outside reserves to the conservation of populations within protected forest ecosystems. In reality, it is through the sustainable management of forests and trees outside reserves that most in situ conservation of forest biological diversity will be realised, though the likelihood of achieving this is greater when protected areas themselves are also well-managed.

This conclusion highlights the roles of indigenous and local communities, and those of the managers of forests and trees outside reserves, in the conservation and sustainable use of forest biological diversity (Articles 8(j)and 10(c)). It similarly emphasises the importance of the rehabilitation and restoration of degraded ecosystems and the recovery of threatened species (Article 8(f)) in the conservation of forest biological diversity, and suggests the use of metapopulation models of population structure and function to design and implement in situ conservation strategies.

A metapopulation perspective on the demographic and genetic dynamics of individual species recognises that populations of a species wax and wane over time, within and across forest ecosystems or reserve boundaries; individuals and populations, variously linked by gene flow to form the overall metapopulation, play a dynamic role in the conservation of genetic diversity. Whilst the fate of specific populations depends on their particular population biology, the decline or demise of individual populations does not threaten the stability of metapopulation or conservation of its genepool, so long as other populations arise. A metapopulation perspective also emphasises the challenges inherent in the identification and monitoring of those components of forest biological diversity important for its conservation and sustainable use.