Chapter 2: Overview of plant genetic resources for food and agriculture
Biological diversity has in practice been defined at three levels – ecosystem, species and genetic diversity – in descending order.1 In addition, a further form of diversity, namely human cultural diversity, has been cited as being inextricably linked to the conservation and sustainable use of natural resources. The term ‘biological resources’ refers more specifically to the physical manifestations of biodiversity which have actual or potential value for humanity.2 Biological resources can be managed, i.e. they can be consumed or replenished and conserved. The way biological resources are managed enhances or reduces biodiversity.3 The world’s biodiversity is not evenly distributed, and generally species’ richness increases with decreasing latitude. Thus species diversity is greatest in the tropics, less in temperate regions and decreases further in polar regions.4 The largest concentration of biodiversity is in the tropical forests which comprise about 7 per cent of the land surface of the Earth and which are estimated to hold more than 50 per cent of all species.5 Many of the countries in which this diversity is concentrated are located in the southern hemisphere and are also those which are economically less developed.6 Agricultural diversity, being a component of biodiversity, is also considered within the three levels of ecosystem, species and genetic diversity.7 One of the primary categories of ecosystems is agricultural ecosystems or agroecosystems, managed by people to meet food, fibre and fuel needs. They have been described as follows:
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