Barren Land

Desertification occurs when the productive potential of land falls by 10 percent or more. When this happens, nondesert areas become more like deserts, a biome in which water is not readily available to the biota and where evaporation rates exceed the precipitation rates. (Desertification does not cause true deserts, which are natural biomes.) Desertification ranges from moderate (10–20 percent drop in productivity) to extreme in which the land supports less than 50 percent of its former productivity and topsoil has been replaced largely by sandy soil.

Desertification caused by the drying conditions associated with climate change usually begins at the edge of land that is already fairly dry. Therefore, desertification expands into existing deserts and the outskirts of grasslands. Desertification caused by human activities occurs at a vulnerable spot and then creeps outward if the climate remains dry. For example, overgrazed ranchland can turn too dry to support grazing and the dry, barren land can spread into adjacent areas.

Forests do not turn into desert spontaneously, but climate change has contributed to a progression of some forest areas into dry barren land. Higher temperatures in the mountains and smaller snowpack melts have contributed to drought, drying of the land, and then severe wildfires. These fires are becoming more frequent as well as hotter and more dangerous as climate continues to change. Furthermore, some places in the United States have suppressed fires to protect homes built in the woods, but this only creates more burnable fuel should a fire strike. Fire, drought, or disease infestation—all events that increase with global warming—kill living things faster than they regrow. Craig Allen, a landscape ecologist in New Mexico, explained the matter for National Geographic in 2008: “This is a dilemma for the Park Service. The projections are that Joshua trees may not survive in Joshua Tree National Park. Sequoias may not survive in Sequoia National Park. What do you do? Do you irrigate these things? Or do you let a 2,000-year-old tree die?” Fire management decisions therefore have an impact on the rate of desertification in some places.

Desertification leads first to soil erosion, which then leads to poor crop production for food for animals and people. Poor crop cover causes more soil erosion, leading to a downward spiral of the land’s quality. In countries suffering severe water stress, the process leads to famine, economic losses, and poorer living conditions. The past few decades have seen a new type of nomad walk the Earth: environmental refugees. Environmental refugees are people forced to migrate from their homelands to find food and water in other places. At the same time, people living in drought may add to the dry conditions by drawing water from sources far away to irrigate the few crops they have left. Bodies of water eventually run dry and the drought worsens.

At its worst, desertification results in parched land with poor drainage that cannot retain moisture, so its water evaporates faster. The high evaporation rate leaves behind dried minerals. Salinization refers to the increased salt levels in evaporated soil; these salts are sometimes called white alkaline salts when they contain arsenic or zinc. Some dry lands in the western United States contain elevated levels of selenium, an element

» condensation—conversion of water vapor into droplets of liquid water

» precipitation—water that falls from the atmosphere to land or to surface waters as rain, snow, sleet, or hail

» infiltration—downward movement of liquid water through soil

» evaporation—conversion of liquid water into gas, or water vapor

» transpiration—movement of liquid water from plant roots, upward in vessels, and into the atmosphere from the leaves as water vapor

Forests serve in the water cycle in two critical ways: transpiration and water storage. Both animals and plants transpire water vapor into the air, but animals transpire as part of aerobic respiration when they exhale moisture from their lungs. Plants and trees possess special cells on the underside of their leaves, called guard cells, that release water vapor from the plant into the atmosphere. The transpiration process begins when warming problem seen today, but it is important to note that natural climate cycles also contribute to drying the land. Specific human influences, other than global warming, that contribute to desertification are the following:

» overgrazing and poor grazing management

» cultivation of sensitive dry lands already at risk of desertification

» deforestation

» intentional or accidental burning of vegetation from arid and semiarid areas

» incorrect irrigation leading to erosion, soil compaction, and salinization

Arid lands are true deserts where little precipitation ever occurs; semiarid lands are dry lands that receive small amounts of precipitation, approximately 10–20 inches (25–50 cm) per year.

Overgrazing has been a major cause of the increased rate of desertification in the past 40 years. For centuries semiarid rangelands supported cattle because herders moved their animals over large ranges to allow the grazed land and its grasses to recover. Early civilizations simply copied the natural grazing-migration behavior practiced by animal herds in North America, Africa, or Asia to this day. These animals followed the seasonal grasses and the pans that filled with water after a rainy season. (A pan is a shallow pool filled in the rainy season and dry in the dry season that supplies water to migrating wildlife.)

Modern grazing includes fencing animals into large but confined ranges. Windmills and irrigation systems supply water to rangelands so that herds do not need to migrate in search of water. Poorly planned wells and irrigation have added to the overall desertification process by pulling the last remaining amounts of water out of the ground. All of these activities have put regions of the world into water-stressed conditions.

Population density and poverty also force people to overwork their land. As mentioned, this process leads to poor crop cover, patchy dry areas, soil erosion, and then further drying. As an example, the Department of Conservation Biology at South Africa’s University of the Western Cape has reported that South Africa loses 330–440 tons (300–400 metric tons) of topsoil each year due to overgrazing and overcultivation. In 2007 a spokesperson for South Africa’s Department of Environmental Affairs explained to a United Nations conference on desertification, “Most of African communities live on agriculture-based economies, and survive by subsistence farming or productivity of marginal lands.” This spokesperson added that the entire problem cannot be placed at the feet of impoverished communities. “However, activities that take place in the developed economies can indirectly contribute to the livelihood of these distant communities due to the global impacts of climate change and desertification.” In short, poverty contributes to environment decay.

Source of Information : Green Technology Conservation Protecting Our Plant Resources