Tuesday, November 14, 2006
K K Vinod
In situ conservation, is the continuation of this traditional method of informal breeding that distinguishes in situ from ex situ conservation on farms and in gardens. However, many developed countries now have legislation protecting plant breeders' rights, which effectively prevents the continuation of traditional agriculture and therefore in situ conservation of crop species. This section therefore applies to in situ conservation of wild species, and of crop species only in those countries where legislation permits.
Sites for inclusion in a network for in situ conservation must be chosen to maximize the diversity that can be maintained. This is similar in principle to choosing sites for collection to maximize diversity collected.
Sites should cover the entire ecological range of the species, with a bias towards its centre(s) of diversity and the ecological extremes of its distribution. There should be a stratified distribution of sites with several levels of clustering: each site should be large enough to encompass a cluster of several genetic populations; each site should be part of a cluster of several nearby sites, close enough for occasional gene flow between sites as a result of rare long-distance dispersal events; each cluster of sites should be part of a larger cluster; and so on to encompass the entire range of the species. Such stratification will serve a dual purpose of: (i) optimizing gene flow within and between populations; and (ii) encompassing the maximum possible range of types of diversity. Within the general stratification, sites and clusters should be chosen to maximize diversity of environments and therefore of selection pressures within and between sites and clusters. As always, of course, diversity of selection pressures is taken to include artificial as well as natural selection, with diversity associated with variation in local preferences and farmers' concepts of quality and agronomic value.
The shape of sites and clusters also needs consideration. For example, linear habitats may be useful to increase connectivity between clusters with minimal increase in areas of the region set aside for conservation. For rare species, there may be a need to create new populations at sites with sufficient connectivity to existing populations to prevent loss of diversity through inbreeding.
Additional measures can be taken to increase biodiversity within the selected network of conservation sites, essentially by increasing the diversity of environments and selection pressures within and between sites.
For crop species, farmers can be actively encouraged to value the distinctiveness of the traditional farming practices of the region; and the local customer community can be actively encouraged to value the distinctiveness of local traditions and their consequent demands on local farmers. Important traditional farming practices can include factors such as conscious selection by the farmer for genetic variation within and between varieties for tolerance to disease, drought, heat, etc. These traditions are based on utilizing high diversity to provide low-cost, sustainable, low-risk protection from environmental stresses and hazards. That is, they benefit not only conservation of biodiversity but also the farm economy.
For wild and some crop species, there can also be opportunities for increasing diversity by appropriately diverse management. Emphasis is on diverse management, as many management procedures, especially mechanized ones, tend to reduce diversity. For example, cutting, liming, fertilization and control of weeds, pathogens and pests are usually applied uniformly across entire sites; in so doing they reduce environmental diversity and therefore the diversity of selection pressures and biodiversity at the scale of the site. If such procedures are also applied consistently from year to year, there will also be less temporal variation in selection pressures, again reducing biodiversity at the scale of the field. In contrast, management by grazing imposes cutting, trampling and fertilization that is spatially and temporally variable - to an extent that depends on the grazing behaviour of the selected herbivore.
Similarly, diversity of management should be encouraged at larger scales, including landscape and regional. The principal problem here relates to how to construct and implement a conservation policy. For example, a management policy may be implemented that maximizes biodiversity within a field; but if that same policy is applied to all sites, the same range of biodiversity will be promoted at all sites, reducing biodiversity at the larger landscape and regional scales. If the policy is to be centrally established and imposed, it may be economically impossible to incorporate the larger-scale variation in management necessary to maximize biodiversity at landscape and regional levels. A decentralized system is likely to be preferable, especially to incorporate regional variations in traditions.
We have seen that biodiversity is a scale-dependent phenomenon and that for its efficient conservation we need to include all scales from a few square centimetres to thousands of square kilometres. We have also shown that the distribution of genetic diversity of any species depends on its life cycle and consequent evolutionary characteristics. Efficient conservation depends on having a good knowledge of population structure and the life cycle characteristics that determine this - dispersal profiles, breeding system and longevity. The same principles apply not only to wild species but also to crop species, the major difference being that crop species have dispersal profiles determined largely by the farmer and market, and are subject to artificial selection by the farmer as well as natural selection.
Forman, R.T.T. (1995) Land Mosaics: the Ecology of Landscapes and Regions.Cambridge University Press, Cambridge.