Excessive Grazing and Browsing
One of the risks particularly associated with arid and semi-arid grazing systems is land degradation as a result of inappropriate grazing - often referred to as overgrazing. The process also occurs in sub-humid and humid grazing systems as well as in temperate and tropical highland grazing systems. Overgrazing is by no means limited to grazing systems and is also likely to become a problem under mixed farming systems.
appropriate grazing can be defined as the practice of grazing too many livestock for too long a period on land unable to recover its vegetation, or of grazing ruminants on land not suitable for grazing as a result of certain physical parameters such as its slope. Overgrazing implies that the number of animals exceeds the productive capacity of the grazing land or pasture. However there may be other factors involved or contributing to the degradation of land under grazing, such as climate change. The environmental problems caused may be soil erosion, the destruction of vegetation, deterioration of water quality and other problems related to these processes.
Usually, overgrazing is the initial process leading to land degradation. Grazing lands are often nutritionally marginal, close to or in arid regions. It is important in these regions that vegetation covers the ground to protect soils from exposure. Overgrazing removes this protective vegetation, while livestock hooves trample exposed soils. These soils are then vulnerable to wind and water erosion, which remove nutritionally rich upper layers of the soil. The process of land degradation can be further aggravated and accelerated by drought. Once exposed and impacted, the soils can no longer support vegetation growth, thus they become desert-like or barren.