Overgrazing is the initial process leading to land degradation. In arid areas it is important that vegetation covers the ground to protect soils. Overgrazing removes this protective vegetation, while livestock hooves trample the 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 more humid zones, overgrazing may result in weed invasion and an overall decrease in forage availability by preferential removal of the more palatable species, and by the consumption of the majority of the more desirable plant species before they have had a chance to set seed.
Expansion of agricultural area and intensification are two ways to increase agricultural output in order to meet the demands of an increasing human population. A common trend is towards increased settlement and crop cultivation in former grazing areas. Under mixed farming systems, the combination of crop cultivation, fuelwood collection, and grazing by livestock on the remaining reduced land area will tend to result in land degradation.
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Livestock Numbers
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Has there been a change in animal numbers or in the type of stock held? For example in some areas there may have been a change resulting in smaller numbers of cattle and greater numbers of smallstock (sheep and goats). Livestock census data, where necessary updated with a field survey, and combined with local consultation with herders and livestock keepers will in most cases provide answers to this question. A change from cattle to small-stock, or the other way round, will inevitably change the nature of the grazing and browsing pressure. |
Increased Grazing Pressure
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Poorly placed resources such as watering points can result in overgrazing of some areas and the underutilization of others.
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Changes in movement patterns
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A change in the freedom of movement of livestock is often an underlying cause of overgrazing. Historic records may be compared with present information on herd and herder mobility. Participatory consultation with livestock keepers and other stakeholders will most likely provide good information. |
Reduction in Communal Grazing Land
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This is often linked to the conversion of the better grazing areas to crop production as one of the responses to increasing human populations and/or to an increased need for cash crops. Information may be available through the same remote sensing data sets as used for vegetation cover, as well as from local records and participatory assessment. Additional information may be available on land registration from land authorities. Consultation will be an essential part of the process of establishing the extent of the problem. Related to this is the fencing of parts of former communal grazing areas - the remaining communal land may no longer be enough to support the numbers of livestock that are needed by households. |
Policy and Institutional changes
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Are there any political or institutional reasons for overgrazing to have taken place? For example, have the imposition or reduction in subsidies (perhaps elsewhere in the World) resulted in any market changes? Has a general deterioration (or increase) in the quality of transportation facilities resulted in a changed market for livestock products? |
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Changes in Vegetation Cover
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Over large areas this can be assessed from a time series of low resolution satellite images using a change in the vegetation index to indicate a change in biomass. The information is widely available and whilst it may be considered as relatively costly, these costs are coming down with the advent of new remote sensing platforms and pricing policies. However, the analysis will have to be carried out by an agency with experience of this technology. |
Change in Species Composition and Abundance
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Invasion of weed species and loss or reduction of key or important indigenous species. This may be recognized by local herders and/or botanists from a local institution. The analysis is likely to be highly subjective unless previous survey work on species composition and distribution (using the same analytical techniques) is available. This analysis is relatively low cost and can be combined with discussions with herders and other stakeholders on pressure / state indicators as long as an interdisciplinary team can be put together for the fieldwork. The use of fixed point photography can contribute to a monitoring programme over a number of years. Similarly, there may be a change in the abundance, distribution and species composition of wildlife. |
Change in Rangeland Quality
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Simple techniques of classification can rapidly build up into an overall assessment of rangeland condition without the need for extensive and time consuming collection of large amounts of specialist data. An example of assessment of range condition for horses in Iceland serves to illustrate the potential of these methods |
Change in Climate
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This will have an effect on rangeland productivity that is independent of direct human induced pressures (ignoring the ultimate causes of climate change). Changes in conditions during the growing season may be indicated by time series of climate data, which are generally available from national meteorological services. Examination of a time series data set should indicate whether a change in weather patterns is a potential contributing factor to land degradation. Time series of satellite data may also provide evidence for change, especially NOAA AVHRR imagery processed to provide a vegetation index (e.g. NDVI). However, the most important use of these data sources will be to emphasize and to quantify the normal annual and seasonal climatic variation, i.e. the variability from year to year, and to place any current evaluations within the context of a longer time-frame. |
Indications of Accelerated Erosion
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Field surveys can establish that accelerated erosion is taking place through the identification of key erosion features such as root pedestals. Again this is subjective unless it can be compared to previous survey work. Such techniques do however, have the advantage of allowing discussion with herders and other stakeholders. Additional data on sediment load in stream s and rivers may also be available from hydrological institutions, indicating changes in erosion. Participatory assessment may also provide qualitative information relating to sediment loads and general water quality in water courses. |
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| Response |
Responses will necessarily depend on the outcomes of any analysis of the above factors, together with any other social and economic considerations. In a majority of cases, the response will initially be limited to pilot schemes and/or limited areas.
On a wider scale, a review of national policies will indicate whether there has been a policy of encouraging arable expansion into range areas, or a privatization of some communal areas. Other policy changes may relate sedentarization of pastoralist groups for social development reasons or as a result of insecurity, famine, drought, or longer term cultural changes.
Uneven grazing distributions can, where practical, be reduced by changing paddock shape, or through fence line relocation (including complete removal and the addition of new fences), paddock sub-division or by the addition, relocation or closing of watering points. Models of animal distribution can assist in the application of these decisions once they are validated for the particular environment in which they are applied.
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| References and Further Reading |
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| Delgado, C., Rosegrant, M., Steinfeld, H., Ehui, S. and Courbois, C. (1999). Livestock to 2020: The next Food Revolution. Food, Agriculture and Environment Discussion Paper 28. Washington DC: International Food Policy Research Institute. Reproduced with permission from the International Food Policy Research Institute www.ifpri.org. The report can be found online at: http://www.ifpri.org/2020/dp/dp28.pdf. The report was jointly produced by IFPRI, FAO, and ILRI. |
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| IFAD (2004). Livestock Services and the Poor. International Fund for Agricultural Development. |
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| LID (1999). Livestock in Poverty-Focused Development, Crewkerne, Somerset: Livestock in Development |
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Livestock, Environment and Development (LEAD) Initiative. (1999). Livestock and Environment Toolbox. Food and Agriculture Organisation of the United Nations. |
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