Land degradation is usually defined as an irreversible change in a land resource. Losses are considered irreversible if recovery would take more than a decade. Three forms of land degradation can be identified:
1. Loss of economic potential to produce goods and services of direct human-use value;
2. Loss of ecological functions necessary to maintain ecosystem processes; and
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3. Loss of biodiversity at the ecosystem, species, or genetic level.
According to Nelson (1988):
1. There is a need for permanent national land monitoring systems to identify emerging and difficult-to-reverse forms of degradation.
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2. Research should focus on management technology and existing socioeconomic systems.
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3. Policy proposals must take into account complexity and local variability.
4. As there appear to be no global or regional solutions to most savanna and arid land degradation problems, progress will depend upon small pilot projects, community experimentation and within-country expertise.
5. The failure and high cost of conventional projects suggests that more progress is likely through attention to enabling incentives that promote spontaneous response across the entire community. The main policy areas are land tenure, taxation and marketing.
6. Many successful strategies will have a strong spatial dimension and involve movement across national and ecological boundaries.
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Monitoring and assessment are vital for the development of an action programme to halt the process of desertification. A unified mapping methodology is a prerequisite for this purpose.
There has been much concern that the misuse and mismanagement of natural resources and industrialization have threatened the precious and limited natural resources. Vast areas are affected by desertification worldwide (Fig. 6.13). In Iran, 80 per cent of the land is arid or semi-arid and desertification is gradually increasing.
Iran is engaged in producing a desertification map of arid lands in Asia, which assess the desertification status, rate, inherent risk, and the pressures exerted by animal and human populations. Under the proposed system, the main desertification types are described as degradation of vegetation cover, water erosion, wind erosion, salinization of agricultural lands and technogenic desertification.
Various information sources such as space photographs, thematic and topographic maps, and statistical information are being used, all of which would be computer processed on the basis of the Geographic Information Systems (GIS).
There occur different types of desertification in various continents and ecosystems. Two main objectives for mapping desertification have been identified: to assist decision-makers to understand the various dimensions of desertification, and to assist scientists to make the best choice in selecting strategies for desertification control to reduce the impact of land degradation. Mapping and landscape dynamics simulation in arid regions prone to desertification is also being undertaken.
Their low productivity, high variability and seasonal diversity mean that many savannas are managed under complex socio-economic arrangements which have evolved over centuries. They are well adapted to all but very recent changes in social, economic and political conditions.
Savannas generally have only limited potential to yield products of value to people. Even in high rainfall areas, savannas are usually less productive than equivalent, temperate agricultural systems. This lower productivity is due mainly to the seasonal distribution of rainfall that characterizes the tropical savanna climate and, also to the low physical and chemical soil conditions common to savanna ecosystems. According to Young and Solbrig (1993), failed savanna development proposals and policy changes are usually characterized by a lack of inventory and ecological assessment.
Savanna ecosystems are very often more episodic, more variable, less predictable and slower to respond than most agricultural systems. Consequently, policy rules are more discretionary, requiring greater financial flexibility.