Inequitable access to land, human population dynamics, and poverty in developing countries are some of the most significant factors that increase overexploitation of deserts. The population of countries with large areas of deserts must often face additional challenges, both political and social, fundamentally derived from the strong competition between users of strategic water and soil resources. These situations of conflict generally result in the concentration wealth in certain sectors of society that, in time, generates territorial imbalances, lack of social equity, and, ultimately, land degradation.

Managing desert ecosystems to maintain their resilience requires an understanding of the interactions among the drivers of change, their dynamics and the thresholds beyond which undesirable changes become difficult to reverse. The key conflict lies in the struggle between human pressures and the inherent fragility of deserts, which defines the complexity of possible responses. Thus, analyses of the problems and the decisions on responses require a multi-pronged approach. It is, essentially, the art of reconciling the needs of local and global communities, and those of humans and other biota.

Responses at the global level

The first surveys of the arid regions of the world included GLASOD, conducted by the International Soil Reference Information Centre (ISRIC) under the auspices of UNEP. Much of the data generated was used in the World Atlas of Desertification published by UNEP in 1992 and 1997. One of the chapters of the recent Millennium Ecosystem Assessment (MA 2005) is devoted to drylands, and addresses, among other topics, dryland ecosystem services, conditions and trends, and drivers of change. The Land Degradation Assessment in Drylands (LADA), starting in 2006, will provide insights on the status and trends of the world's drylands. LADA is being implemented through a partnership consisting of different United Nations agencies, international agricultural research centres, farmers' associations, universities, and other civil society organizations; FAO and UNEP are jointly implementing this project. LADA will establish a standardized methodological framework to address the process of dryland degradation, increase countries' capacity to analyze and assess the causes of land degradation and areas at risk, and promote actions to control land degradation.

Many of the global conventions organized by the United Nations are responses to global degradation (Box 4.3). The Ramsar Convention, in particular, has played a strategic role on the protection of oases and other desert wetlands. However, there is no global or regional response strategy focused exclusively on true deserts. The two international conventions signed in 1992 - the Framework Convention on Climate Change and the Convention on Biological Diversity - during the United Nations Conference on Environment and Development (also known as UNCED or the Rio Earth Summit) make almost no reference to the environmental issues of deserts. In 1994, the United Nations Convention to Combat Desertification in those Countries Experiencing Serious Drought and/or Desertification, particularly in Africa (also known as UNCCD) was adopted by the international community. This convention put a strong emphasis on the sustainable development of the arid, semi-arid and sub-humid drylands of the world, which were defined as "areas in which the ratio of annual precipitation to potential evapotranspiration falls within the range from 0.05 to 0.65." Thus, the text of the convention includes arid deserts, but excludes the hyper-arid deserts of the world as a focus of its concern, while at the same time, it includes a very large area of nondesert ecoregions where land degradation is a serious problem.

Thus, although UNCCD is not directly focused on desert environments, it does address some of the most pressing issues of land degradation that take place mostly on the deserts' edges. Additionally, UNCCD is a very important response of the international community to the threat of land degradation in drylands, and its implementation has helped in the strategic coordination and cooperation of responses at all levels - national, sub-regional, regional and international, to prevent and control land degradation, and to promote the rehabilitation of degraded areas.

Responses at regional and national levels

Apart from the international efforts that are currently being implemented, many countries are also developing their own internal policies, and making independent efforts to protect their desert environments. Although an exhaustive list would be impossible within the scope of this report, some interesting cases can be analyzed that highlight the problems of land degradation in the deserts of different regions, and the responses on a regional basis.

In an effort to make better use of the investments in water-control structures in northern Africa, for example, a series of protection measures were implemented in watersheds in national programmes in Tunisia and Morocco. In many countries of North Africa, and also in Yemen, soil and water conservation are part of the traditional knowledge that desert societies have used for thousands of years. This knowledge has helped them adapt to aridity and drought, with sustainable land management practices that allow for soil regeneration, harvesting and conservation of water, and retention of suspended sediments in traditional terraces.

The risks of drought and water mismanagement are constant threats in deserts. To address them, there are a number of suggested technologies and practices, such as improved fallow, microbasins, windbreaks, and earth and soil bunds. Premised on concepts of sustainability, especially in those aspects emphasizing the importance of horizontal cooperation, many of these technologies have acquired new force with more participationoriented and integrated approaches developed since the mid-1980s. The system implemented by the local stakeholders in Gobabeb, within the Namibian desert, is a hopeful example of an organized regional response (see Box 6.4). Longterm results of research at Gobabeb focus on the variable, arid environment with a particularly high diversity of invertebrates, and contribute to understanding the basic principles underlying the functioning of arid systems (Figure 4.10).

Salinity and high sand content are major constraints in the Asian deserts. The planting of trees to help manage the spread of salt in the landscape requires large efforts. Irrigated portions of warm, arid areas in Pakistan, India, and China are major agricultural production areas but often face declining yields as a result of soil salinization.

In China, the deterioration of the plant cover in the headwaters of the Yangtze River has created major flooding problems. Massive efforts are now required to deal with the enormous problem of water erosion in the Loess Plateau, one of the most eroded regions of the world, on account of intensive agricultural practices on the steep mountain slopes. Because of the deterioration of water reserves, monitoring groundwater levels and confronting salinity problems have become essential management tools, especially in the North China plain.

In Central Asia, many of the countries of the Commonwealth of Independent States have problems of chemical soil contamination as in Kazakhstan, salinization in the irrigation areas of the Aral Sea Basin, and soil erosion in Kyrgyzstan and Tajikistan. All have prompted organized responses centered on the identification of the processes involved and sustainable management. Unfortunately, given the political and economical crises of the region, the implementation of urgently needed responses has been slow.

Since the introduction of its National Soil Conservation Program in 1983, Australia has substantially expanded and improved its soil and water conservation technologies on private and public lands. The national and state governments continue to develop and implement sustainable land management policies, including a program of substantial reform of soil conservation, vegetation, forestry, and environmental planning law and policy. The focus of current efforts is on diversification of the commercial use of agricultural land, encouragement of conservation and remediation, strengthening natural resource management institutions, monitoring effects of changes, development of new extension and education capabilities, and controlling urban settlements on highly productive agricultural land. The national government has made a substantial financial contribution for carrying out local "governmentcommunity" conservation projects. Australia's experience has become an emblematic case of organization for controlling degradation.

In the case of Latin America, land degradation in deserts - especially salinization caused by poorly-managed irrigation systems - has been one of the main factors promoting rural emigration into urban slums, or the massive exodus of rural workers into more developed regions, looking for new alternative livelihoods. The Mexican Meseta Central, the Brazilian arid Caatinga, and the Argentine High Monte, are major sources of immigration for their countries' industrialized cities, or, in the case of Mexico, for the United States.