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Land degradation is a concept in which the value of the biophysial environment is affected by one or a combination of human-induced processes (eg floods, soil erosion, bush fires) acting upon the land. Natural hazardsare excluded as a cause.
Land degradation is a global problem, largely related to agricultural use. The major causes include:
- Land clearance, such as clearcutting and deforestation;
- Agricultural depletion of soil nutrients through poor farming practices (eg shifting cultivation without adequate fallow periods, no or poor soil conservation measures, cultivation of fragile or marginal lands, unbalanced fertilizer use);
- Livestock including overgrazing
- Faulty planning or management of irrigation, and overdrafting
- Urban sprawl and commercial development
- Land pollution including industrial waste
- Vehicle off-roading
The main consequence of land degradation is a substantial reduction in the productivity of the land. The major stresses on vulnerable land include:
- Accelerated soil erosion by wind and water
- Soil acidification or alkalinisation
- Salinination
- Destruction of soil structure including loss of organisc matter
- Soil damaged by industrial or other development activities, and rendered derliect (although it may be brought back to use only after soil remediation)
Overcutting of vegetation occurs when people cut forests, woodlands and shrublands - to obtain timber, fuelwood and other products - at a pace exceeding the rate of natural regrowth. This is frequent in semi-arid environments, where fuelwood shortages are often severe.
Overgrazing of natural pastures at stocking intensities above the livestock carrying capacity often results in a decrease in vegetation cover and is a leading cause of wind and water erosion.
Severe land degradation affects a significant portion of the earth's arable lands, decreasing the wealth and economic development of nations. According to the Guardian newspaper, it is estimated that up to 40% of the world's agricultural land is seriously degraded. Land degradation cancels out gains advanced by improved crop yields and reduced population growth. As the land resource base becomes less productive, food security is compromised and competition for dwindling resources increases, and the arise potential risks of famine and conflict.
Without effective land rehabiitation measures, a downward spiral of eco-social spiral problems can result as marginal lands become depleted of nutrients due to unsustainable land management practices resulting in lost soil resilience, leading to soil degradation and permanent damage.
Land degradation is frequently assumed (incorrectly) to effect only soil fertility. But its effects are often more significantly affect receiving water courses (rivers, wetlands and lakes) since soil, along with nutrients and contaminants associated with soil, are delivered in large quantities to environments that respond detrimentally to their input. As a result, l;and degradation has potentially disastrous effects on lakes and reservoirs that are designed to alleviate flooding, provide irrigation, and generate hydroelectricity.
Earthwtach – the UN’s system-wide mechanism to coordinate, harmonize and catalyze environmental observation activities for integrated assessment purposes, has drawn attention to the linkages between desertification and poverty. (Box 4.7).
Box 4.7: Earthwatch views on land degradation
Land degradation has affected some 1900 million hectares of land word-wide. In Africa an estimated 500 million hectares of land have been affected by soil degradation, including 65% of the region's agricultural land. The rate at which arable land is being lost is increasing and is currently 30-35 times the historical rate. The loss of potential productivity due to soil erosion world wide is estimated to be equivalent to some 20 million tons of grain per year. And this is happening worldwide, not just in Africa or Asia (UNEP 1999).
The understanding of the extent and causes of this phenomenon - "desertification", however incomplete, is now far too clear for the global community to ignore. In some cases the cause could be solely natural or purely human, but often both human and natural causes combine to accelerate desertification. However the graphic talk of marching sand dunes and expanding deserts distracts attention from the real problem - the continuing human impact of the degradation of the dry lands on the millions of desperate people facing hunger and despair.
There are close linkages between desertification and poverty. No long-term strategy of poverty eradication can succeed in the face of environmental forces that promote persistent erosion of the physical resources upon which poor people depend. No programme for protecting the environment can succeed without alleviating day-to-day pressures of poverty. These pressures leave people little choice but to discount the future so deeply that they fail to protect the resource base to ensure their own and their children's well being. The feminization of poverty in areas affected by desertification is an aspect that must not be ignored. Strategies to improve and safeguard the local environment should be built on the knowledge and resourcefulness of local women, and remove their special burdens and constraints (UNEP 2000).
The negotiation and signature of the Convention to Combat Desertification by June 1994 was a major post-Rio accomplishment, providing a mechanism to assess and respond to the problems of dryland degradation around the world.
Source: http://earthwatch.unep.net/emergingissues/desertification/landdegradation.php |
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