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Wastelands
Finally, humans have long played a role in making deserts, but not the kind that are particularly good for wildlife or people. Many human activities can degrade marginal lands, i.e., those that are nearly deserts, and drive them over the edge.
"Good examples include land degradation as a result of vegetation loss due to grazing and/or drought," says Nicholas Lancaster, researcher and director of the Center for Arid Lands Environmental Management at the Desert Research Institute in Reno, Nev. His list of most desert-degrading human activities is topped by surface disturbance by off-road vehicles and animals, increasing salinity of agricultural lands due to poor irrigation practices, scarce water resources, and overuse of surface water and groundwater, and urbanization of growing populations.
Overgrazing of animals and poor agricultural practices, both of which cause massive soil loss and erosion, takes about 12 million hectares of marginal lands out of use every year, according to an online report by the American Association for the Advancement of Science (AAAS).
This is not only bad for desert wildlife, but it's a human tragedy. Some examples: Since 1965, degradation of already marginal lands on the edge of the Sahara Desert forced one-sixth of the people of Burkina Faso and Mali to flee to cities. Between 1965 and 1988, in Mauritania, the proportion of nomads who grazed animals on the land fell from 73 percent to 7 percent, while the population of the capital city Nouakchott shot up from 9 percent to 41 percent, according to AAAS.
Global warming is also making itself known in the American deserts. The mysterious die-off of vast stands of piñon trees — the source of pine nuts valued by humans and wildlife — may be from hotter summers in the higher elevation deserts of Arizona and New Mexico.
The warming climate is also tinkering with where, when and how much rain falls in deserts, although the specifics are still unclear. Some desert regions may get greener. Others may experience droughts that last for decades — potentially drying up entire cities.
Good News
But there is good news. Some marginal lands that were thought to be on the verge have been brought back from the brink. One example is the Machakos District in Kenya. In the 1930s, it was thought to be a lost cause. But over the decades, despite a population explosion, water and soil conservation measures have improved the land.
These measures include cutting hillside terraces to stop soil erosion and digging water-storage ponds, according to work by Mary Tiffin of Drylands Research in the United Kingdom. New farming methods have also helped in densely populated, semi-arid areas of northern Nigeria, according to Tiffin and her colleagues.
So, even though many deserts are becoming a lot less deserted, there's no reason they have to become wastelands as well.
