Desertification - expansion of the desert - is a grave problem that affects not only those countries in the direct path of the encroaching arid lands, but also has implications for the rest of the world. To give some idea of the scale of the problem, the last 50 years have seen the Sahara desert spread southwards to cover an extra 65 million hectares, and on a global scale, the area of useful land lost each year exceeds 6 million hectares.
Desertification is brought about by our planet's progressively changing climate - the world is becoming warmer and drier, and this means there is less water to support plants and animals. However, the natural rate of desertification has been greatly increased as a result of exploitation by the desert's human inhabitants. The causes of this increase are similar in many ways to those that bring about deforestation, and once again, the chief culprit is agriculture.
People have been farming the land for thousands of years, cultivating the soil to grow crops and rearing animals for food and transport. Traditionally, the land is "rotated" to ensure that the soil can rest after use. However, to meet the demands from an ever-growing population, it has been necessary to reduce the amount of time during which land is left fallow. As a result, the soil has become degraded, and in some cases unable to support cultivation.
Continual growing of crops in soil depleted of nutrients is often combined with over-grazing by domesticated animals such as goats, cattle, sheep and camels, as well as cutting down trees and shrubs for fuel. This can have disastrous effects on the fragile desert ecosystem, removing all the natural vegetation cover, and exposing what little soil is left to the ravages of wind, rain and sun. Soil and plants have a two-way relationship in which neither can survive without the other. Most plants need soil in which to root. This anchors them to the ground and stops them being blown away, whilst also providing them with essential water and nutrients. Soil is dependent upon plants for two main reasons. First, plants provide most of the material from which new soil is made, and second, plant roots help to hold the soil together and prevent it from being eroded by the wind and rain.
The adverse effects of agriculture on the desert are not restricted to its edges. The cultivation of crops requires large amounts of water, a resource that is in short supply in arid lands. To tackle this problem, farmers have developed irrigation systems to bring water from springs, oases and underground sources elsewhere in the desert. In many cases this does not pose a threat to the environment, and centuries of experience have taught farmers how to extract water with minimum environmental impact. However, the increased pressure placed on food producers by population growth has led to the adoption of unsustainable irrigation practices, draining in a very short space of time the water sources which may have taken thousands of years to accumulate.
The climatic extremes of the deserts make them extremely fragile ecosystems. With such a small amount of water available to support wildlife, any disturbance is potentially disastrous. All ecosystems exist in a more or less delicate balance, and the desert is perhaps the most extreme case. With all forms of life linked to one another, a change in the availability of water can affect the smallest plants and the largest animals alike.
photo courtesy of WWF-UK
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