"Land degradation" is a catchall term covering such problems as wind and water erosion, soil pollution by urban wastes or pesticides and the buildup of mineral salts caused by improper irrigation. In other words, land degradation can take many forms, but always entails a serious disruption of a healthy balance between five key ecosystem functions. These are: food production; fibre provision; microclimate regulation; water retention; and carbon storage. Its impacts can be far-reaching, including loss of soil fertility, destruction of species habitat and biodiversity, soil erosion, and excessive nutrient runoff into lakes. Land degradation also has serious knock-on effects for humans, such as malnutrition, disease, forced migration, cultural damage and, even, war. At its worst, land degradation can result in the desertification or abandonment of land (or both).
One-quarter of Earth’s ice-free land area is subject to human-induced, anthropocentric degradation. The rate at which we are eroding soils (on which all our food is currently grown) is far higher than the rate at which soil is formed by natural processes. According to a 2018 report of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES), worsening land degradation caused by human activities is undermining the well-being of two fifths of humanity, driving species extinctions and intensifying climate change. It is also a major contributor to mass human migration and increased conflict, according to the world’s first comprehensive evidence-based assessment of land degradation and restoration. Land degradation costs the equivalent of about 10% of the world’s annual gross product in 2010 through the loss of biodiversity and ecosystem services.
There are eleven principal threats to land: agriculture, vegetation clearing, feral animals, fire, forestry, grazing, mining, salinization, tourism, urbanization and weeds. The two most significant direct causes of land degradation are the conversion of native vegetation into crop and grazing lands and unsustainable land-management practices: deforestation; poor management of arable and pasture land, including over-use of fertilizers and pesticides, the clearance of steep slopes and marginal land for cultivation, inadequate soil conservation and overgrazing; poor management of watersheds and water resources; uncontrolled dumping of wastes; deposition of pollutants from the air; and poor land-use planning. Other factors include the effects of climate change and loss of land to rapid urbanisation, infrastructure and mining.
However, the underlying driver of all these changes is rising per-capita demand from growing populations for protein, fibre and bioenergy. This in turn leads to more demand for land and further encroachment into areas with marginal soils. Market deregulation, which has been a global trend since the 1980s, can lead to the destruction of sustainable land management practices in favour of monocultures, and can encourage a race to the bottom as far as environmental protection is concerned. The vast geographical distance between demand for consumer goods and the land needed to produce them – between, in other words, the cause of land degradation and its effect – makes it much harder to address the problem politically.
The International Soil Reference and Information Centre (ISRIC), in the Netherlands, estimates that since 1945 Homo sapiens has degraded 17 percent of the world's land, not counting wastelands like Antarctica and the Gobi Desert. Two thirds of the devastated area will require major restoration.
According to the IPBES (2018) report, 43% of world populations live in regions affected by land degradation. The problem is growing most rapidly in sub-Saharan Africa, Asia and South and Central America. The report predicts that the combined effects of land degradation and climate change will have displaced between 50 million and 700 million people by 2050, potentially triggering conflict over disputed land. However, it would be wrong to infer that land degradation is purely a problem for developing countries. Overall, land is more degraded in richer nations in the developed world – as shown, for example, by greater declines in soil organic carbon content (a measure of soil health) and probably related to industrial farming. And while the rate of degradation has slowed, people in these regions are generally less vulnerable to its effects.
Land degradation has reduced fertility and agricultural potential. Replacing lost top soil takes centuries or even millennia. These losses have negated many of the advances made through expanding agricultural areas and increasing productivity.
The USA has the most carefully measured soil in the world. Every five years the U.S. Department of Agriculture evaluates the nation's land, county by county, in terms of something called "the universal soil loss equation," which assesses the soil movement in a given area. In the 1980s three independent studies used the data to estimate actual soil loss. All concluded that the peril to U.S. agriculture from erosion is negligible.
Even in Africa, the problem is bad luck, bad weather, and bad planning. Traditionally, African villagers held land in common, with access regulated by unwritten cultural rules. In those circumstances the people responsible for the management of the land take overuse into account, so they enforce rules of access that limit the use of the land. When modern crops and agricultural techniques appear, the system comes apart, because yields shoot high enough to give people a greater incentive to cheat. Population pressures exacerbate the problem by shrinking everyone's share of the common land. Add drought or ethnic conflict and the result is disaster. But African nations without drought or conflict have done increasingly well. The 1992 harvest in Nigeria was the biggest in twenty years. Given half a chance, people in Africa seem to make their own way.
As for other parts of sub-Saharan Africa, no one denies the famine there. Yet recent independent studies have found no long-term environmental consequences of the recent and devastating drought; the southern border of the desert, one study shows, is in about the same place it was eighty years ago, suggesting that the desert expands and contracts with little regard for its human inhabitants. The drought may have led to temporary overuse of common property, but the proper response would be to adjust land-use rules – change the zoning, so to speak – as societies did in other parts of Africa. That this has failed to occur in sub-Saharan Africa says more about the pervasive corruption, inefficiency, and civil turmoil there than about the inherent evils of breeding.