Desertification, whether from natural or human causes, is a process that is seemingly permanent and irrevocable. Desertification has been reversed in some places, but the best defense against desertification is the good offense of prevention.
This terrible consequence of bad land and riparian zone management has led to famine, ruined economies and dust storms the likes of which have never been seen before. The rising rate of devastating dust storms that threaten Beijing, China alone were caused by human activity and have triggered the most massive and desperate attempt to restore the soil in the history of mankind.
The general process of desertification:
Fertile topsoil is very delicate. It retains its structure when there are three elements: root structures, decomposing plant material, and a plant canopy.
Rain is quite powerful in its ability to break down topsoil. One drop can bear down on delicate topsoil with considerable force that multiplies with more drops of rain. When the plant canopy is lost, there is nothing to prevent rain from bashing into the soil and digging out channels. Once the channels become deep and large enough, even more powerful rivulets of water will form to wash even more soil away.
Once the delicate topsoil is washed away, the finer and less stable soils and sands underneath dry out and are more easily blown away by the wind. This process of taking a beating from raindrops, then drying out and being blown away by the wind goes on until there is nothing that would allow a plant canopy to grow. There are no nutrients or structure that will support plants.
The worst desertification has occurred on the African continent, in China, in the American Dust Bowl crisis and in Latin America. Semi arid areas are the most susceptible, as with the American west.
There are several ways in which desertification occurs: Nutrient depletion through bad crop management or natural means; erosion from cutting too much timber or otherwise denuding the land; diversion of waterways; and the power of natural events.
Soil nutrient depletion:
The most common way to deplete the soil is to run too many crops that pull nutrients out of the soil and into the plant. When the plant returns nothing to the soil, there will be no nutrients to support new plantings. Over planting, failure to rotate crops, and extended drought are the main triggers for soil nutrient depletion. When the soil cannot support a plant canopy, then the rains and winds can go to work on what used to be the fertile top layers.
Erosion from eliminating the plant canopy:
Over grazing constantly eliminates the plant canopy before a new canopy can properly form. There were great problems between sheep farmers and cattle growers when the American west was being settled because sheep will eat any plant and will eat plants to the ground.
The hooves of cattle and other large, compacted herds will also compress wet soil, which will then harden when dry. This makes it impossible for seeds to gestate and break through to the surface. This is just another way in which protective plant canopies are prevented from forming because of too much large animal grazing activity.
Deforestation, whether for the timber, to get the plants out of the way, or for structural development, will eliminate the plant canopy and expose the delicate fertile topsoil to the pounding rains, rushing rivulets, and moving winds.
Structural development will put something over the soil, but the soil will be permanently compacted by the weight of buildings, roadways, human traffic, or concreted areas. Compacted soil makes it difficult for useful plants to grow. Worse, the soil can be made toxic by chemical or oil leaks, poor toxic chemical disposal methods, and spills.
Diversion of waterways:
Waterway diversion is a tricky game to play with nature. When entire river drainage systems could not be clearly seen with the naked eye, then no one knew that nasty surprises would occur. When the water systems were diverted from their natural courses, the only source of moisture for some areas was eliminated, the plant canopies died, and the desertification processes began.
In other cases, water has been successfully diverted and directed to turn desert into lush areas of farmland and crop land. Southern and northern California use water diversion, where the plentiful water of the north state has been corralled by a series of dams and levees. These systems provide flood control in the north and water storage and delivery to the south. In the arid months of the year, the water is sent via a major canal to the mid and southern farming portions of the state.
This is not an perfect system, because water also must flow through the Sacramento Valley delta and then to the San Francisco Bay in order to sustain those watery ecosystems. The water battles can be quite fierce in California.
Riparian mismanagement is an issue wherever there is land that comes up against any type of waterway. The stream, creek, river, bay, lake or ocean interacts with the land to create underground water tables that feed the surrounding trees and shrubs. Any denuding of the soil that causes the soil to wash into the waterway can clog or divert the water, can make the water cloudy and low in oxygen, and cause any number of troubles.
In riparian mismanagement, anything that disrupts the water table and causes the nearby plant canopies to die will lead to soil erosion and potential “mini” desertification.
It is well known that the grand deserts of the Western United States were once lush jungles and rain forests. Theories of vast meteorite or asteroid impacts, glacial movement and evaporation, or just the whims of nature explain how the lush Edens to turned into the magnificent deserts that are still full of sturdy and resilient flora and fauna.
Landslides, fires, and earthquakes will change the nature of the Earth’s surface, washing vast areas clean, burning millions of acres of rich forest, or downloading millions of tons of rock. Forest fires that are actually the only way for some species of pine cones to explode, spread the seeds and cause new trees to grow. Forest fires are most often caused by lightning strikes and often occur in areas that are isolated and protected national forests.
But forest fires in developed areas can be a devastating and sudden way to kill a plant canopy, leaving delicate soil exposed to rains and winds. While erosion and landslides may occur, however, the forest soil is usually too rich to stay without a plant canopy for long. Plant seeds blow in the winds, are carried and dropped by birds, or are carried in the fur and paws of animals. The seeds take hold easily, and when the forests are left alone, rich plant canopies begin anew.
The Napa and Sonoma Valleys of California are famed for their wine because of the topsoil of that vast area contains ash that came from an ancient and massive volcanic eruption.
Even the Mount St. Helen volcanic disaster could not keep the plant canopy from carrying out its incredible will to return and to thrive.
In conclusion, perhaps there will be a way to reverse the desertification that has been done to large swaths of the planet. For now, there are lessons learned and policies established that could, with a lot of help, prevent any more human caused desertification from happening.