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مُساهمة  Admin في السبت مايو 08, 2010 3:53 am

Countering desertification

[وحدهم المشرفون لديهم صلاحيات معاينة هذه الصورة]

Desertification is recognized as a major threat to biodiversity. Some countries have developed Biodiversity Action
Plans to counter its effects, particularly in relation to the protection of endangered flora and fauna.[13][14]
A number of methods have been tried in order to reduce the rate of desertification; however, most measures treat symptoms of sand movement and do not address the root causes of land modification such as overgrazing, unsustainable farming and deforestation. In developing countries under threat of desertification, many local people use trees for firewood and cooking which has increased the problem of land degradation and often even increased their poverty. In order to gain further supplies of fuel the local population add more pressure to the depleted forests; adding to the desertification process.
Techniques focus on two aspects: provisioning of water (e.g. by wells and energy intensive systems involving water pipes or over long distances) and fixating and hyper-fertilising soil.
Fixating the soil is often done through the use of shelter belts, woodlots and windbreaks. Windbreaks are made from trees and bushes and are used to reduce soil erosion and evapotranspiration. They were widely encouraged by development agencies from the middle of the 1980s in the Sahel area of Africa. Another approach is the spraying of petroleum or nano clay[15] over semi-arid cropland. This is often done in areas where either petroleum or nano clay is easily and cheaply obtainable (eg Iran). In both cases, the application of the material coats seedlings to prevent moisture loss and stop them being blown away.
Some soils (e.g. clay), due to lack of water can become consolidated rather than porous (as in the case of sandy soils). Some techniques as zaï or tillage are then used to still allow the planting of crops.[16]
Enriching of the soil and restoration of its fertility is often done by plants. Of these, the Leguminous plants which extract nitrogen from the air and fixes it in the soil, and food crops/trees as grains, barley, beans and dates are the most important.
When housing is foreseen in or near a reforestation area, organic waste material (e.g. hazelnut shells, bamboo, chicken manure) can be made into biochar or Terra preta nova by a pyrolysis unit. This substance may be used to enrich planting spaces for high-demanding crops.[17]
Finally, some approaches as stacking stones around the base of trees and artificial groove-digging also help increase the local success of crop survival. Stacked stones help to collect morning dew and retain soil moisture. Artificial grooves are dug in the ground as to retain rainfall and trap wind-blown seeds. [18][19]
In order to solve the problem of cutting trees for personal energy requirements, solutions as Solar ovens and efficient wood burning cook stoves are advocated as a means to relieve pressure upon the environment; however, these techniques are generally prohibitively expensive in the very regions where they are needed.
While desertification has received some publicity by the news media, most people are unaware of the extent of environmental degradation of productive lands and the expansion of deserts. In 1988 Ridley Nelson pointed out that desertification is a subtle and complex process of deterioration.
At the local level, individuals and governments can temporarily forestall desertification. Sand fences are used throughout the Middle East and the US, in the same way snow fences are used in the north. Placement of straw grids, each up to a square meter in area, will also decrease the surface wind velocity. Shrubs and trees planted within the grids are protected by the straw until they take root. However, some studies suggest that planting of trees depletes water supplies in the area.[20] In areas where some water is available for irrigation, shrubs planted on the lower one-third of a dune's windward side will stabilize the dune. This vegetation decreases the wind velocity near the base of the dune and prevents much of the sand from moving. Higher velocity winds at the top of the dune level it off and trees can be planted atop these flattened surfaces.

Jojoba plantations, such as those shown, have played a role in combating edge effects of desertification in the Thar Desert, India.
Oases and farmlands in windy regions are often protected by the approach described above by planting tree fences or grass belts in order to reduce erosion and walking dunes. Also, small projects as oases often section their plot of land by placing a barrier of thorny bushes or other obstacles to keep grazing animals away from the food crops. Instead, they provide water provisioning (eg from a well, ...) outside this barrier. They provide this service mainly to accommodate the animals of travelers (eg camels, ...). Sand that manages to pass through the grass belts can be caught in strips of trees planted as wind breaks 50 to 100 meters apart adjacent to the belts. Small plots of trees may also be scattered inside oases to stabilize the area. On a much larger scale, a "Green Wall of China", which will eventually stretch more than 5,700 kilometers in length, nearly as long as the Great Wall of China, is being planted in north-eastern China to protect "sandy lands" – deserts created by human activity.
There is another technique, which is controversial, that involves using livestock to rehabilitate land. This is based on the fact that many areas in the world which are heavily desertified were once grasslands and similar environments (the Sahara, areas in the USA that were affected by the Dust Bowl years[21]) and where substantial populations of large herbivores were once supported. By using livestock (which is contained within a portable fence so that they cannot wander away from the site) along with hay and seeds contained within, the land can be restored effectively, even on mine dumps.[22] In addition, people that hold livestock and that have a semi-nomadic livestyle (moving between fixed homes) such as nomadic pastoralists have significant interest in combating desertification of these areas.[23] Having these people to plant shelterbelts, windbreaks, trees or nitrogen-fixating crops in the vicinity of their homes would also help a lot.
Africa, with coordination from Senegal, has launched its own "green wall" project[24]. Trees will be planted on a 15 km wide land strip from Senegal to Djibouti. Aside from countering desert progression, the project is also aimed at creating new economic activities, especially thanks to tree products such as gum arabic [25]
More efficient use of existing water resources and control of salinization are other tools for mitigating arid lands. New ways are also being sought to find groundwater resources and to develop more effective ways of irrigating arid and semiarid lands. Research on the reclamation of deserts is also focusing on discovering proper crop rotation to protect fragile soil, on understanding how sand-fixing plants can be adapted to local environments, and on how overgrazing can be addressed. A proposal combining desert stabilization and renewable energy is Aerially Delivered Re-forestation and Erosion Control System - [26]


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تاريخ التسجيل : 28/04/2010

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