Land degradation is a process in which the value of the biophysical environment is affected by a combination of human-induced processes acting upon the land. It is viewed as any change or disturbance to the land perceived to be deleterious or undesirable. Natural hazards are excluded as a cause; however human activities can indirectly affect phenomena such as floods and bush fires.
Expert projections suggest that land degradation will be an important theme of the 21st century, impacting agricultural productivity, biodiversity loss, environmental change, and its effects on food security. It is estimated that up to 40% of the world's agricultural land is seriously degraded.
According to the Special Report on Climate Change and Land of the Intergovernmental Panel on Climate Change: "About a quarter of the Earth's ice-free land area is subject to human-induced degradation (medium confidence). Soil erosion from agricultural fields is estimated to be currently 11 to 20 times (no-tillage) to more than 100 times (conventional tillage) higher than the soil formation rate (medium confidence).".
The United Nations estimate that about 30% of land is degraded worldwide, and about 3.2 billion people reside in these degrading areas. About 12 million hectares of productive land – which roughly equals the size of Greece – is degraded every year. This happens because people exploit the land without protecting it. The United Nations Sustainable Development Goal 15 has a target to restore degraded land and soil and achieve a land degradation-neutral world by 2030.
Consequences
There are four main ways of looking at land degradation and its impact on the environment around it:
A temporary or permanent decline in the productive capacity of the land. This can be seen through a loss of biomass, a loss of actual productivity or in potential productivity, or a loss or change in vegetative cover and soil nutrients. Action in the land's capacity to provide resources for human livelihoods. This can be measured from a base line of past land use. Loss of biodiversity: A loss of range of species or ecosystem complexity as a decline in the environmental quality. Shifting ecological risk: increased vulnerability of the environment or people to destruction or crisis. This is measured through a base line in the form of pre-existing risk of crisis or destruction.
A problem with defining land degradation is that what one group of people might view as degradation, others might view as a benefit or opportunity. For example, planting crops at a location with heavy rainfall and steep slopes would create scientific and environmental concern regarding the risk of soil erosion by water, yet farmers could view the location as a favourable one for high crop yields.
Different types
In addition to the usual types of land degradation that have been known for centuries (water, wind and mechanical erosion, physical, chemical and biological degradation), four other types have emerged in the last 50 years: pollution, often chemical, due to agricultural, industrial, mining or commercial activities; loss of arable land due to urban construction, road building, land conversion, agricultural expansion, etc.; artificial radioactivity, sometimes accidental; land-use constraints associated with armed conflicts.
Overall, more than 36 types of land degradation can be assessed. All are induced or aggravated by human activities, e.g. soil erosion, soil contamination, soil acidification, sheet erosion, silting, aridification, salinization, urbanization, etc.
Causes
Land degradation is a global problem largely related to agricultural use, deforestation and climate change. Causes include:
Land clearance, such as clearcutting and deforestation
Agricultural depletion of soil nutrients through poor farming practices
Livestock including overgrazing and overdrafting
Inappropriate irrigation and overdrafting
Urban sprawl and commercial development
Vehicle off-roading
Quarrying of stone, sand, ore and minerals
Increase in field size due to economies of scale, reducing shelter for wildlife, as hedgerows and copses disappear Exposure of naked soil after harvesting by heavy equipment Monoculture, destabilizing the local ecosystem Dumping of non-biodegradable trash, such as plastics Invasive Species Climate change Loss of soil carbon
Overcutting of vegetation occurs when people cut forests, woodlands and shrublands—to obtain timber, fuelwood and other products—at a pace exceeding the rate of natural regrowth. This is frequent in semi-arid environments, where fuelwood shortages are often severe.