Land degradation
Serious land degradation in Nauru after the depletion of the phosphate cover through mining
Land degradation is a concept in which the value of the biophysical environment is affected by one or more combination of human-induced processes acting upon the land.[1] Natural hazards are excluded as a cause, however human activities can indirectly affect phenomena such as floods and bushfires.
It is estimated that up to 40% of the world's agricultural land is seriously degraded.
Causes
Overgrazing by livestock can lead to land degradation
Land degradation is a global problem, largely related to agricultural use. The major causes include:
- Land clearance, such as clearcutting and deforestation
- Agricultural depletion of soil nutrients through poor farming practices
- Livestock including overgrazing
- Irrigation and overdrafting
- Urban sprawl and commercial development
- Land pollution including industrial waste
- Vehicle off-roading
- Quarrying of stone, sand, ore and minerals
Effects
Soil erosion in a wheat field near Pullman, USA.
The main outcome of land degradation is a substantial reduction in the productivity of the land.[3] The major stresses on vulnerable land include:
- Accelerated soil erosion by wind and water
- Soil acidification or alkalinisation
- Salination
- Destruction of soil structure including loss of organic matter
- Derelict soil
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. The phenomenon is significant in three countries here; it is the leading factor in Iran.
Overgrazing is the grazing of natural pastures at stocking intensities above the livestock carrying capacity; the resulting decrease in the vegetation cover is a leading cause of wind and water erosion. It is a significant factor in six countries, and by far the most important in Afghanistan.
Agricultural activities that can cause land degradation include shifting cultivation without adequate fallow periods, absence of soil conservation measures, cultivation of fragile or marginal lands, unbalanced fertilizer use, and a host of possible problems arising from faulty planning or management of irrigation. They are a major factor in Sri Lanka and the dominant one in Bangladesh.
The role of population factors in land degradation processes obviously occurs in the context of the underlying causes. In the region, in fact, it is indeed one of the two major basic causes of degradation along with land shortage, and land shortage itself ultimately is a consequence of continued population growth in the face of the finiteness of land resources. In the context of land shortage the growing population pressure, during 1980-1990, has led to decreases in the already small areas of agricultural land per person in six out of eight countries (14% for India and 22% for Pakistan).
Population pressure also operates through other mechanisms. Improper agricultural practices, for instance, occur only under constraints such as the saturation of good lands under population pressure which leads settlers to cultivate too shallow or too steep soils, plough fallow land before it has recovered its fertility, or attempt to obtain multiple crops by irrigating unsuitable soils.
Severe land degradation affects a significant portion of the earth's arable lands, decreasing the wealth and economic development of nations. Land degradation cancels out gains advanced by improved crop yields and reduced population growth. As the land resource base becomes less productive, food security is compromised and competition for dwindling resources increases, the seeds of famine and potential conflict are sown.
Unless land rehabilitation measures are effective a downward eco-social spiral is created when marginal lands are nutrient depleted by unsustainable land management practices resulting in lost soil resilience leading to soil degradation and permanent damage.
See also: Soils retrogression and degradation
We often assume that land degradation only affects soil fertility. However, the effects of land degradation often more significantly affect receiving water courses (rivers, wetlands and lakes) since soil, along with nutrients and contaminants associated with soil, are delivered in large quantities to environments that respond detrimentally to their input.
Land degradation therefore has potentially disastrous effects on lakes and reservoirs that are designed to alleviate flooding, provide irrigation, and generate hydroelectricity.
Climate change
Significant land degradation from seawater inundation, particularly in river deltas and on low-lying islands, is a potential hazard that was identified in a 2007 IPCC report.[citation needed] As a result of sea-level rise from climate change, salinity levels can reach levels where agriculture becomes impossible
