Land Degradation

Definitions of Land Degradation
A common definition of desertification is as land degradation in the drylands (" 'Desertification' means land degradation in arid, semi-arid and dry sub-humid areas."), yet the two terms are often used as if they are distinct (e.g., "Land degradation and desertification in desert margins" by Reich et al. 2000). The CCD also defines "land" by its primary productivity service (" 'land' means the terrestrial bioproductive system.") and "land degradation" as an implicit loss of provision of this service (" 'land degradation' means reduction or loss of the biological or economic productivity .'). The definition of biological productivity and economic benefit depends on users' priorities - transforming woodland to cropland may decrease biological productivity, degrade the economic benefit of firewood production but increase the economic benefit of food production. With respect to the mechanisms of land degradation - changes in the properties of the land (soil, water, vegetation) do not correspond linearly to changes in productivity. Loss of productivity can also be attributed to non human-induced factors such as rainfall variability and human factors such as low labor input. Thus, a range of interacting variables that affect productivity should be addressed in order to assess objectively and unambiguously land degradation.Commonly considered degradation processes are vegetation degradation, water and wind erosion, salinization, soil compaction and crusting, and soil nutrient depletion. Pollution, acidification, alkalization, and water logging are often important locally (Oldeman, 1994; Lal, 2001; Dregne, 2002). Field experiments, field measurements, field observations, remote sensing, and computer modeling are carried out to study these processes. The higher the aggregation level in each of these study approaches, the more problematic each of the methods becomes, either because of upscaling issues or because of questionable extrapolations and generalizations.


Causes, Drivers and Types of Land Degradation
Desertification is caused by a combination of factors that change over time and vary by location. These include indirect factors such as population pressure, socioeconomic and policy factors, and international trade as well as direct factors such as land use patterns and practices and climate-related processes. Desertification is taking place due to indirect factors driving unsustainable use of scarce natural resources by local land users. This situation may be further exacerbated by global climate change. Desertification is considered to be the result of management approaches adopted by land users, who are unable to respond adequately to indirect factors like population pressure and globalization and who increase the pressure on the land in unsustainable ways. This leads to decreased land productivity and a downward spiral of worsening degradation and poverty. Where conditions permit, dryland populations can avoid degradation by improving their agricultural practices and enhancing pastoral mobility in a sustainable way. On the whole, the interaction between climatic factors and human responses can create a range of different outcomes. To counter the problems effectively, it is important-but difficult-to distinguish between those resulting from the natural conditions of dryland ecosystems and those caused by unsustainable management practices as well as broader economic and policy factors.

Impacts of Land Degradation
Desertification has environmental impacts at the global and regional scale. Affected areas may sometimes be located thousands of kilometers away from the desertified areas. Desertification-related processes such as reduction of vegetation cover, for instance, increase the formation of aerosols and dust. These, in turn, affect cloud formation and rainfall patterns, the global carbon cycle, and plant and animal biodiversity. For example, visibility in Beijing is often adversely affected by dust storms originating in the Gobi Desert in springtime. Large dust storms emanating from China affect the Korean peninsula and Japan and are observed to even have an impact on North American air quality. ...The societal and political impacts of desertification also extend to non-dryland areas. Droughts and loss of land productivity are predominant factors in movement of people from drylands to other areas, for example (medium certainty). An influx of migrants may reduce the ability of the population to use ecosystem services in a sustainable way. Such migration may exacerbate urban sprawl and by competing for scarce natural resources bring about internal and cross-boundary social, ethnic, and political strife. Desertification-induced movement of people also has the potential of adversely affecting local, regional, and even global political and economic stability, which may encourage foreign intervention.

Indicators of Land Degradation
Desertification is the consequence of a set of important degradation processes in the Mediterranean environments, especially in semi-arid and arid regions, where water is the main limiting factor of land use performance on ecosystems. Environmentally Sensitive Areas (ESAs) to desertification around the Mediterranean region exhibit different sensitivity to desertification for various reasons. For example there are areas presenting high sensitivity to low rainfall and extreme events due to low vegetation cover, low resistance of vegetation to drought, steep slopes, highly erodible parent materials, etc. High sensitivity can be also related to the type of land use for the cases that it promotes desertification in climatically and topographically marginal areas. For example cereals cultivated in hilly areas with soils formed on marl present a serious threat for desertification. Furthermore, there are areas which are sensitive to desertification for special reasons, such as fire risk, which is likely to generate runoff and erosion problems for some years; rambla and flood plain environments, where fluctuating phreatic levels may show salinization and toxicity problems; and exotic tree plantations, where poor ground cover and autotoxicity may lead to higher runoff and sediment yields. The various types of ESAs to desertification can be distinguished and mapped by using certain key indicators for assessing the land capability to withstand further degradation, or the land suitability for supporting specific types of land use. The key indicators for defining ESAs to desertification, which can be used at regional or national level, can be divided into four broad categories defining the qualities of soil, climate, vegetation, and management (stressor indicators). This approach includes parameters which can be easily found in existing soil, vegetation, and climate reports.