The environmental degradation of arid and semi-arid areas through overcultivation, overgrazing, deforestation, and bad irrigation practices. Changing climatic patterns are also implicated. The land loses its fertility, and is no longer able to support its population. The problem is worsened in many regions by climatic instability (particularly drought), by rapidly-growing populations, and by cash cropping, which reduces the area available for the production of food crops for the local population. In the 1970s and 1980s, desertification occurred at one time or another in most of the Sahel.
Desertification is the degradation of land in arid, semi arid and dry sub-humid areas resulting from various factors including climatic variations, but primarily human activities. Modern desertification usually arises from the demands of increased populations that settle on the land in order to grow crops and graze animals.
A major impact of desertification is biodiversity loss, and loss of productive capacity, such as the transition from grassland dominated by perennial grasses to one dominated by perennial shrubs. In the southwestern deserts of the United States, semiarid ecosystems dominated by perennial bunchgrasses, including blue grama and black grama, have been replaced by shrublands dominated by creosotebush since the early 1900s. The change in vegetation is thought to have induced desertification in this region. In the Madagascar central highland plateau, virtually ten percent of the entire country has been lost to desertification due to slash and burn agriculture by indigenous peoples.
Causes
In some regions around the world, deserts are separated sharply from surrounding, less arid areas by mountains and other contrasting landforms that reflect basic structural differences in the terrain. In other areas, desert fringes form a gradual transition from a dry to a more humid environment, making it more difficult to define the desert border. Small hollows support vegetation that picks up heat from the hot winds and protects the land from the prevailing winds.
In these marginal areas human activity may stress the ecosystem beyond its tolerance limit, resulting in degradation of the land. By pounding the soil with their hooves, livestock compact the substrate, increase the proportion of fine material, and reduce the percolation rate of the soil, thus encouraging erosion by wind and water.
In large desert areas, sand dunes can encroach on human habitats. When these skipping particles land, they may knock into other particles and cause them to skip as well.
It is a common misconception that droughts cause desertification. Continued land abuse during droughts, however, increases land degradation. Increased population and livestock pressure on marginal lands has accelerated desertification. In some areas, nomads moving to less arid areas disrupt the local ecosystem and increase the rate of erosion of the land. Nomads are trying to escape the desert, but because of their land-use practices, they are bringing the desert with them.
Some arid and semi-arid lands can support crops, but additional pressure from greater populations or decreases in rainfall can lead to the few plants present disappearing.
This degradation of formerly productive land is a complex process. Desertification may intensify a general climatic trend toward greater aridity, or it may initiate a change in local climate. Desertification does not occur in linear, easily mappable patterns. Areas far from natural deserts can degrade quickly to barren soil, rock, or sand through poor land management. The presence of a nearby desert has no direct relationship to desertification. Unfortunately, an area undergoing desertification is brought to public attention only after the process is well underway.
Prehistoric patterns
Desertification is a historic phenomenon; Paleodeserts, large sand seas now inactive because they are stabilized by vegetation, extend well beyond the present margins of core deserts, such as the Sahara.
Through dated fossil pollen, it has been found that today's Sahara desert has been changing between desert and fertile savanna.
Historical and current desertification
See, Timeline of environmental eventsOvergrazing and to a lesser extent drought in the 1930s transformed parts of the Great Plains in the United States into the "Dust Bowl". Improved agricultural and water management have prevented a disaster of the earlier magnitude from recurring, but desertification presently affects tens of millions of people with primary occurrence in the lesser developed countries.
Desertification is widespread in many areas of the People's Republic of China. While there has been an increase in livestock, the land available for grazing has decreased.
Human overpopulation is leading to destruction of tropical wet forests and tropical dry forests, due to widening practices of slash-and-burn and other methods of subsistence farming necessitated by famines in lesser developed countries. A sequel to the deforestation is typically large scale erosion, loss of soil nutrients and sometimes total desertification. Examples of this extreme outcome can be seen on Madagascar's central highland plateau, where about seven percent of the country's total land mass has become barren, sterile land.
Overgrazing has made the Rio Puerco Basin of central New Mexico one of the most eroded river basins of the western United States and has increased the high sediment content of the river.
The Desert of Maine is a 40-acre dune of glacial silt near Freeport, Maine.
Countering desertification
Desertification has been recognized at an international level as a major threat to biodiversity.
A number of solutions have been tried in order to reduce the rate of desertification and regain lost land.
With many of the local people using trees for firewood and cooking the problem has become acute. thus adding to the desertification process.
While desertification has received tremendous publicity by the political and news media, there are still many things that we don't know about the degradation of productive lands and the expansion of deserts. In 1988 Ridley Nelson pointed out in an important scientific paper that the desertification problem and processes are not clearly defined. There is no consensus among researchers as to the specific causes, extent, or degree of desertification. Contrary to many popular reports, desertification is actually a subtle and complex process of deterioration that may often be reversible.
At the local level, individuals and governments can help to reclaim and protect their lands. In areas of sand dunes, covering the dunes with large boulders or petroleum will interrupt the wind regime near the face of the dunes and prevent the sand from moving. 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.
Oases and farmlands in windy regions can be protected by planting tree fences or grass belts.
More efficient use of existing water resources and control of salinization are other effective tools for improving arid lands. New ways also being sought to find and tap groundwater resources and to develop more effective ways of irrigating arid and semiarid lands. Research on the reclamation of deserts also is focusing on discovering proper crop rotation to protect the fragile soil, on understanding how sand-fixing plants can be adapted to local environments, and on how grazing lands and water resources can be developed effectively without being overused.
Off-road vehicles significantly increase soil loss in the delicate desert environment of the western United States, which can be controlled by restrictions on such vehicles.
User Comments Add a comment…