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Habitat degradation and loss

The focus of conservation action has recently shifted from protecting individual species to conserving habitats and ecosystems. An illustration of how conservation plans are now conceived at broader scales is provided by WWF International which recently developed priorities for action at the scale of ecoregions (large areas of relatively uniform climate that harbour a characteristic set of species and ecological communities). Ecoregions of particular conservation importance include Lake Baikal in Russia, the Australian Great Barrier Reef and the Atlantic forests of Argentina, Brazil and Paraguay.

Loss and degradation of habitat is the most important factor causing loss of species. For example, conversion of forests or grasslands into croplands results in the local extinction of plant and animal species (Sala and others 2000). Worldwide about 1.2 million km2 of land have been converted to cropland in the past 30 years. In a recent global survey, habitat loss was found to be the principal factor affecting 83 per cent of threatened mammals and 85 per cent of threatened birds (Hilton-Taylor 2000, BirdLife International 2000). Habitat modification arises from many different types of land use change including agricultural development, logging, dam construction, mining and urban development.

Over the past three decades, major losses of virtually every kind of natural habitat have occurred. For example, FAO assessments show that between 1980 and 1995 forest cover in developing countries declined by an estimated 2 million km2 - an average annual loss of 130 000 km2 (FAO 1999a). The most important causes of forest loss included conversion toagriculture and development schemes involving resettlement. As a result, habitats such as the tropical dry forests of Central America have virtually disappeared (UNDP, UNEP, World Bank and WRI 2000). In terms of loss of species, freshwater habitats are the most degraded, with some 20 per cent of freshwater species having become extinct or threatened with extinction in recent decades (UNDP, UNEP, World Bank and WRI 2000). The main causes of extinctions among freshwater fishes are declines in habitat quality (Harrison and Stiassny 1999).

Dryland ecosystems, which cover more than onethird of the world's land area, are particularly vulnerable to degradation. Statistics indicate that more than 250 million people are directly affected by desertification (UNCCD 2001). In 1977, 57 million people failed to produce enough food to sustain themselves as a result of land degradation and by 1984 this number had risen to 135 million (UNEP 1992). Impacts of degradation on dryland biodiversity have not been comprehensively documented but substantial changes have resulted from grazing of livestock, deforestation, introduction of non-native species and conversion to croplands (UNEP 1995). In response, the 1977 United Nations Conference on Desertification adopted a Plan of Action to Combat Desertification. Despite this, assessments by UNEP (1992) indicated that land degradation in many dryland areas had continued to intensify. As a result the United Nations Convention to Combat Desertification was developed, entering into force in 1996. This convention aims to promote effective action through local programmes and international partnerships.

Global number and area of protected sites by year

Total area of protected areas has increased from some 2.78 million km2 in 1970 to more than 12 million km2 by 2000

Note: areas of more than 1 000 ha, IUCN categories I-VI

Source: compiled from Green and Paine 1997 and UNEP-WCMC 2001b

Wetlands are areas where the water table is at or near the surface of the land, or where the land is covered by shallow water, and include areas of marsh, fen and peatland. Wetlands play an important role in regulating water flow and are of exceptional importance as habitats for large numbers of species. Wetland habitats are also of high economic importance for provision of water and fisheries (more than twothirds of the world's fish harvest is linked to coastal and inland wetland areas). Concern about degradation and loss of wetland habitats led to the development of the Convention on Wetlands of International Importance Especially as Waterfowl Habitat (Ramsar) in 1971. The Ramsar Convention provides a framework for national action and international cooperation for the conservation and wise use of wetlands and their resources (see Chapter 1 for more information).

The designation of protected areas, such as national parks, is one of the most widely used approaches for conserving habitats. In addition to national parks, a total of 167 sites have now been designated as natural heritage sites under the World Heritage Convention. The total area of protected sites has increased continuously during the past three decades from less than 3 million km2 in 1970 to more than 12 million km2 by the late 1990s (Green and Paine 1997), indicating that there are continuing efforts by governments to establish protected areas. Although the effectiveness of protected areas for conserving biodiversity has been questioned, a recent analysis of 93 protected areas around the world indicated that most parks are successful at stopping land clearing and to a lesser extent at mitigating logging, hunting, fire and grazing (Bruner and others 2001).

The most significant response to the biodiversity crisis during the past 30 years has been the Convention on Biological Diversity (CBD) which entered into force in December 1993 and had been signed by 182 Parties by December 2001. The convention has three main goals: the conservation of biodiversity; sustainable use of the components of biodiversity; and sharing the benefits arising from the use of genetic resources in a fair and equitable way (see Chapter 1).

The CBD has resulted in major activity at both national and international levels, and in the increased coordination of cross-sectoral action within and between countries. However, major challenges remain in increasing capacity to assess biodiversity and its value to people, securing adequate financial resources for conservation actions, and building political support for the changes necessary to ensure biodiversity conservation and sustainable use.

It is clear from national reports that the implementation of the convention is making progress in most countries, as illustrated by preparation of national biodiversity strategies and action plans, increasing efforts to reform institutional and legislative arrangements, integration of biodiversity into sectoral activities and increased recognition by governments of the importance of the identification and monitoring of biological diversity.

It is not yet possible to assess accurately the impacts of the CBD on biodiversity, partly because the CBD has been in force for only a short time. In addition, the parties to the convention have yet to develop any globally applicable criteria and indicators by which overall changes in biodiversity can be measured. It is clear that the convention has had some impact at the policy level in many countries. What remains difficult to assess is the depth of commitment to implementation and how any such policy changes may result in changes in the state of biodiversity. This issue is addressed in the strategic plan for the convention, currently under discussion.