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. | Environmental Assessment: Pressure State Response Indicators Overgrazing Policy Pressure and Policy Options( Communal System) Overgrazing Policy Pressure and Policy Options ( Ranching Systems) Technology Options

Inappropriate 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. | (Click on photo to view an enlarged picture)

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.

In humid and sub-humid zones, overgrazing may cause weed invasion and a decrease in forage availability.

A common trend is towards increased settlement by people practicing crop cultivation in former grazing areas. Under mixed farming systems, the processes of crop cultivation and fuelwood collection may become the main factors leading to land degradation, rather than livestock grazing. More commonly, land degradation in mixed farming systems will result from a combination of all these factors. Through a supply of manure, livestock can go some way towards assisting in mitigation of the negative impacts that crop cultivation can have on the environment.

Overgrazing may result in:

- Reduced ground cover.
- Increased or accelerated erosion: by wind, runoff, and dune mobilisation as a result of reduced ground cover.
- Loss of vegetation as a result of selective grazing or browsing. This may result in a loss of palatable forage species and an increase in less palatable and less nutritious forage species.
- Increasing species rarity as a result of excessive grazing or browsing.
- Bush encroachment
- Weed invasion, or an increase in undesirable (including exotic) plant species

A livestock planner may suspect that there is a problem of accelerated erosion resulting from overgrazing. If there is overgrazing he needs to find out why it is happening.

The root cause of overgrazing may be one or more of the following factors:

- Stock numbers may be increasing, perhaps as a result of increasing human population.
- The composition of livestock herds may be changing. These changes may themselves be driven by a complex set of factors.
- There may be a net loss of grazing area to arable farming.
- Seasonal mobility may be restricted by political unrest, by fencing or by other causes.
- Changes in access to water resources may be restricting movement and denying access to parts of formerly accessible rangelands.

Most indigenous management systems, especially those in arid and semi-arid lands, were developed in environments where the quality of the land was not determined only by human use and management. For example, most pastoralist societies in East Africa have the preservation of good grazing as the main objective of traditional land management. At present, there is a reduction in grazing resources not only because of overgrazing, but also as a result of bush encroachment, which in some instances may be the dominant indicator of land degradation. Bush encroachment results, to a great extent, from the disappearance of large browsers like elephants, rhinos, and giraffes. The control of fire may also lead to an increasing dominance of bush and other woody vegetation at the expense of grassland. As grazing ecosystems become impoverished, land management must cope with new problems, to which traditional approaches may no longer be applicable.

There is also the important related point: what actually is land degradation? There can be no doubt that land is degraded when there are signs like deep gullies with deforestation. Such land, in the eyes of the ecologist, is severely degraded because there are only a few remaining plant species and a productivity breakdown. Meanwhile, controlled deforestation when it leads to a well managed and sustainable pasture might not be considered as a degradation, refering to social, economical as well as ecological criteria.

In relation to sustainable development, the mode of land management and land degradation assessment should be closely linked to the issues of potential use.

Note: Pasture degradation is a concept different to that of land degradation.

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