A balanced ecosystem is a healthy ecosystem. In a healthy dryland ecosystem, relatively few animals and humans attempt to survive on the limited resources of the land, which include water, fertile soil and trees. Since rainfall is infrequent in semiarid regions, the land is not built to support huge fields of crops or supply grazing land for hundreds of thousands of cattle.
The root cause of desertification is poor soil conservation leading to soil degradation. Healthy, productive soil is rich with organic matter called humus [source: Ball]. Humus is formed when decaying organic materials like dead plants and animals are transformed by micro-organisms and fungi into soil that's rich in essential nutrients like carbon, nitrogen, phosphorous and sulfur [source: International Institute for Sustainable Development].
Unsustainable farming methods also contribute to soil degradation. Crop rotation, heavy composting and responsible use of chemical fertilizer ensure that the soil has enough organic imput to support vibrant micro-organisms. On the other hand, overuse of chemical fertilizers, failure to employ crop rotation and irresponsible irrigation practices rob the soil of the last of its nutrients. When topsoil is depleted of humus, it's either too loose or too compacted, both of which can lead to destructive erosion.
All life depends on the quality and fertility of the soil. Plants can't grow when soil is allowed to degrade. This means no food crops for humans and no grazing crops for animals. All the rain in the world won't help infertile topsoil. It will only wash away.
Perhaps the greatest cause of soil degradation and desertification is an explosion in world population, particularly in developing countries. Throughout the 1990s, dryland regions experienced a population growth of 18.5 percent, mostly in desperately poor, developing nations [source: GreenFacts.org]. In their daily struggle to survive, these expanding populations have put a deadly strain on their environment.
Grazing animals are just as bad. Grasses are essential to anchoring arid topsoil in a dryland region. When animals are allowed to graze recklessly, they remove all of the native grasses, exposing the topsoil to destructive erosion forces like winds and sudden thunderstorms.
Firewood is the fuel of choice for many people living in developing countries. This has led to unchecked clear-cutting of forests in dryland ecosystems. Trees play a crucial role in anchoring down topsoil and slowing down the force of winds. When too many trees are removed, windstorms and dust storms ensue.
Human activities also exacerbate the biggest problem of living in a dryland region: lack of rainfall. When land is cleared of plant life, either from overgrazing or logging, the bare surface of the Earth reflects more of the sun's light back into the atmosphere, creating even hotter temperatures. In semiarid regions, higher temperatures cause a higher rate of evaporation, which means even less rainfall. Also, all of the dust kicked up by cattle and the smoke created by wildfires introduces heavy particles into the atmosphere that make it more difficult for rain drops to form [source: Socioeconomic Data and Applications Center].
Even political conflicts and war contribute to desertification. When war refugees flee from invading armies, they move en masse into some of the most marginal ecosystems in the world. They bring with them their native farming grazing practices, which can be highly unsuitable for their new home.
In the next section, we'll talk in depth about who is most affected by desertification.