Desertification

by: Gen

Part I
Deserts

How would you describe a desert? A place which is always hot, and dry, with very little vegetation? Well, that perception is wrong in one area. A desert is not a place which is ALWAYS HOT... a desert can be cold as well... freezing even! In definition, a desert is a region so arid because of little rainfall that it supports only sparse and widely spaced vegetation or no vegetation at all.

Now for a few Did You Know's:

Did You Know - approximately 1/5 of the Earth's land surface is desert?
Did You Know - in the Eastern Saharan Desert, on average, clouds cover the sun for fewer than 100 hours of the year?
Did You Know - that some deserts have gone thousands of years without any measurable rain?

For some reason, deserts have a reputation for supporting very little life... when it is quite the contrary. Deserts usually high very high biodiversity, including animals that remain hidden during daylight hours to control body temperature or to limit moisture needs.

Desert landscapes are often composed of sand and rocky surfaces. Cold deserts have similar features but the main form of precipitation is snow rather than rain. The largest cold desert is Antarctica (made of about 98% thick continental ice sheet and 2% barren rock). The largest hot desert is the Sahara.

Deserts usually have extreme temperature range. Most deserts have a low temperature at night. This is because the air is very dry and therefore holds very little heat so as soon as the sun sets, the desert cools very quickly.

Part II
Desertification

Desertification is the degradation of land in arid, semi arid and dry sub-humid areas resulting from different things such as climate and human activities. Modern desertification often happens due to increased populations that settle on the land in order to grow crops and graze animals.

In some regions of the world, deserts are separted sharply from surrounding less arid areas by mountains and other contrasting landforms that reflect basic structural differences in regional geology. In other areas, desert fringes form a gradual transition from a dry place to a more humid enviroment, making it more difficult to define the desert border. These transition zones have very fragile, delicately balanced ecosystems.

In these marginal areas human activity may stress the ecosystem beyond its tolerance limit, resulting in degredation of the land. By pounding the soil with their hooves, livestock compact the substrate, increase the proportion of fine material therefore encouraging erosion by wind and water.

In large deserts, sand dunes can move to human habitats. Sand dunes can move in different ways, all help by wind. With enough wind, particles collide in mid-air, causing sheet flows. In a major dust storm, dunes may move tens of meters through such sheet flows. And like snow, sand avalanches, falling down the steep slopes of the dunes that face away from the winds, also moving the dunes foward.

Some arid and semi-arid lands can support crops, but additional pressure such as greater populations or decreases in rainfall can lead to the few plants present to dissapearing. The soil becomes eroded. With the removal of shade, rates of evaportation increase and salts become drawn up to the surface. This is salinisation, and inhibits plant growth. The loss of plants causes less moisture to be retained in the area, which may change the climate pattern leading to lower rainfall.

Part III
Countering Desertification

Deserification has been recognized as a major threat to biodiversity. Consequently, numerous countries have developed Biodiversity Action Plans to counter its effects, particularly in relation to the protection of endangered flora and fauna.

Many solutions have been tried in order to reduce the rate of desertification and regain lost land. Leguminous plants which extract nitrogen from the air and fix it in the soil, can be planted to restore fertility. Stones stacked around the base of trees collect morning dew and retain soil moisture. Artifical groves can be dug in the ground to retain rainfall and trap wind-blown seeds. In Iran, petroleum is being sprayed all over semi-arid land with crops. This coats seedlings to prevent moisture loss and stops them from being blown away. Windbreaks made from trees and bushes to reduce soil erosion and evapotranspiration was widely encouraged by development agencies from the middle of the 1980s in the Sahel area of Africa.

In a more local level, individuals and governments can help. In areas with sand dunes, covering the dunes with large boulders or petroleum will interupt the wind near the face of the dunes and prevent the sand from moving. Sand fences are used across the Middle East and the US, in the same way snow fences are used up north. Placement of straw grids, each up to a square meter in area, will also decrease the surface wind velocity.