Overgrazing is the practice of allowing more animals to feed on a given piece of land for a longer time than it is able to support. Overgrazing can subtly damage the environment by altering the kinds of plants able to grow in a certain area, or more conspicuously by destroying most plants and leaving bare ground. Many kinds of animals are responsible for overgrazing in different parts of the world. In the United States, cattle cause much of the damage by overgrazing. Goats, sheep, horses, and even yaks are responsible for the majority of damage in some other countries. Although overgrazing is often associated with domesticated animals, uncontrolled populations of wild animals, including deer, can cause similar problems.
Ranchers and herders can minimize or eliminate the problem of overgrazing by careful management of their herds. Moving animals to new pasture before the vegetation is cropped too short is one important strategy. Allowing sufficient recovery time before returning animals to an already grazed pasture is also vital. Even one animal, if kept in a single pasture for long periods of time, will overgraze the plants by eating the newest growth first and selecting only the plants that it likes best.
Historical Background and Scientific Foundations
Herding animals, particularly sheep, is a very ancient occupation in Europe, Asia minor, and Africa. Sheep provided meat, milk, and skins for early farmers; this versatility made them a valuable supplement to agricultural subsistence. The value placed on sheep in the ancient world can be seen in Homer’s Odyssey, in which the giant Cyclops tenderly cares for his flocks. With the advent of spinning, sheep became the major source of fiber fo clothing. Later, other animals such as cattle and goats were also domesticated. When relatively small numbers of animals were able to roam on large areas of land, over-grazing was not a problem. However, as more people and animals started to compete for finite grazing resources, additional stress was placed on the ecosystem, leading to environmental damage.
Overgrazing results when too many animals are kept on too little land for the plants to recover sufficiently before being grazed again. Because most grazing animals are selective about the plants they eat, the desirable, nutritious plants are usually consumed first, leaving less-appetizing plants to grow to maturity and disperse their seeds. If allowed to continue, this eventually results in the less-desirable plants displacing the desirable ones, leaving the land unsuitable for grazing. This problem is especially serious if the unwanted plants are thorny or poisonous.
Furthermore, if animals are allowed to graze on most grasses for too long before being moved, they can damage the root growth of the plants. Just as when a lawn is mowed too short, the plants cannot generate enough energy through photosynthesis to grow. If its roots are too small during periods of drought, the plant is likely to die because it cannot access enough water. In this way, overgrazing can lead to the death of all the plants in a particular area, leaving the ground too dry and sterile to support new growth.
Impacts and Issues
Overgrazing is a serious problem because it harms both the environment and the animals it is intended to benefit. Plants that have been overgrazed are less healthy because their carbohydrate reserves have been depleted. Animals who are fed on this less-nutritious fodder are not as healthy as their well-fed counterparts, are more
WORDS TO KNOW
FODDER: Food for grazing animals.
GRAZING CAPACITY: The number of animals that a given area of land can support.
PASTURE: Low-growing plants suitable for grazing livestock or land containing such plants. Some pastureland is fenced, while some is part of the open range.
vulnerable to severe winter weather, produce weaker offspring, and calve less often. All of these factors increase costs and decrease income for herders and ranchers, many of whom lack the financial reserves to weather hardship.
Among the environmental costs of overgrazing is the destructive way in which it alters the ecosystem of grasslands. By eating certain plants and not others, the balanced composition of the turf is altered. Some grazing animals will pull up plants by the roots if forced to feed in overgrazed pastures. Plant roots are important soil stabilizers and removing them can lead to erosion of the most fertile topsoil. Erosion can also occur after overgrazed plants die off during drought. In extreme cases, overgrazing can lead to desertification, the process by which an ecosystem is transformed into a desert. In China, geological studies have determined that overgrazing on the steppes directly led to the burial of fertile soils under desert sands about 300 years ago, turning formerly productive land into unusable desert. It is also possible to directly observe the difference in climate between well-managed and overgrazed pasture land. For example, the average ground temperature in the overgrazed Mexican Sonora desert is higher than the ground temperature in adjacent areas of the United States by about 7°F (4°C), leading to increased air temperatures
Access to pasture land and disagreement over land use have been the subject of heated litigation in the United States. In many western states, ranchers pay for access to federal land on which they graze their herds. Although some federal land is closed to grazing to protect the ecosystem, some ranchers assert that they have the right to use the land despite the government’s prohibitions. Furthermore, environmental groups have sued the federal government, alleging environmental damage from overgrazing. In some instances, they have succeeded in halting grazing on federal land, further antagonizing the relationship between ranchers, regulatory bodies, and environmentalists. Although all these groups agree that overgrazing is a dangerous problem, they differ on the definition of overgrazing. Ranchers become concerned that overly strict definitions of overgrazing will damage their livelihoods, while environmentalists worry that irreparable damage is being done by lax management of overgrazing
Often the problems associated with overgrazing are particularly difficult to solve because they are the product of poverty and economic necessity rather than of
IN CONTEXT: DEADLY CONSEQUENCES OF OVERGRAZING
A 7.6-magnitude earthquake in Kashmir, Pakistan, on October 8, 2005 killed at least 79,000 people. Another 65,000 people were reported to have been injured and more than 32,000 buildings collapsed. Although substantial, the Kashmir earthquake produced waves only 1/100 as large and released energy only 1/1,000 as great as the 1964 Alaskan earthquake (magnitude 9.2). Each increment of magnitude, for example from 7 to 8, corresponds to a ten-fold increase in seismic wave height and a thirty-two-fold increase in the amount of energy released. According to statistics compiled by the U.S. Geological Survey, there are on average fourteen earthquakes of magnitude 7.0 to 7.9 and one of magnitude 8.0 to 8.9 somewhere in the worl each year. Thus, the Kashmir earthquake was a large but not unprecedented event.
Most of the deaths and injuries associated with the 2005 Kashmir earthquake occurred when buildings collapsed and buried their inhabitants. There were many reports of people swept away or buried by landslides during the days immediately after the earthquake. In other cases, landslides closed roads and hindered rescue efforts in the remote and mountainous region.
Analysts assigned much of the blame for the post-earthquake landslides to deforestation and to overgrazing on steep hills and mountainsides. Both deforestation and overgrazing are chronic problems throughout the Himalayan region.
simple mismanagement. Worldwide, the demand for meat has increased dramatically in recent years and is forecast to double by 2050. Herders, many of whom are quite poor, are raising more animals to maximize their benefit in the booming market. In fact, by overgrazing the land, they are raising weaker animals; the loss from overgrazed lands amounts to billions of dollars annually. In many places, particularly in Asia and Africa, herders are exceeding the grazing capacity of the land by 50% or more. Mongolia and several western Chinese provinces have seen severe overgrazing in an attempt to feed China’s economic boom and subsequent demand for meat. The effects of overgrazing can already be seen in the more than 3,950 square mi (2,000 square km) of Chinese land that becomes desert every year.
In the United States, ranchers and agricultural academics have made significant progress toward minimizing overgrazing. Research into the best grazing practices for different types of animals and climates is continuing, and some simple guidelines for pasture rotation have been developed. Most overgrazing in the United States is typically confined to small areas, but overgrazing on Native American reservations is a particular problem.
Around the world, the extent of overgrazing is much greater, with more people relying on the scarce resources provided by their stressed land and herds. Good management practices—such as supplementing animal fodder with agricultural waste like corn stalks—and an understanding of appropriate grazing rotation will help minimize the damage of overgrazing. However, as long as animal numbers remain so high above the land’s capacity for support, the problems associated with overgrazing will continue.
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Kenneth T. LaPensee
Overgrazing is one of the most critical environmental problems facing the western United States. Rangelands have been mismanaged for over a hundred years, mainly due to cattle grazing. In addition to consuming vegetation, cattle alter the ecosystem of rangeland by tramping, urination, defecation, and trashing. Degradation due to heavy livestock grazing continues to occur in many diverse and fragile ecosystems, including savanna , desert , meadow, and alpine communities.
Riparian lands, highly vegetated, narrow strips of land bordering rivers or other natural watercourses, make up only two percent of rangelands, but have the most diverse populations of vegetation and wildlife . Overgrazing has had a devastating effect on these areas. Cattle eat the seedlings of young trees, which has led to the elimination of some species , and this has reduced the species of birds in these areas and disrupted migratory patterns. Lack of new tree growth in riparian areas has also resulted in the drying up of stream beds and the loss of habitat for fish and amphibians. It has contributed to the problem of soil erosion , desertification and the greenhouse effect . Other rangeland ecosystems are facing similar disruption.
The Bureau of Land Management (BLM) part of the U. S. Department of the Interior is the largest landholder in the United States. They are responsible for 334 million acres of land which fall under multiple-use mandates. The BLM leases much of this public land to individuals for grazing purposes, charging ranchers approximately $1.35 per month to graze one cow and a calf. It has been estimated that the fair market value for such forage is $6.65, and the agency has come under attack for leasing grazing rights at extremely low rates. It has also been criticized for allowing abusive land management practices. Critics claim that those who utilize these public lands try to maximize profits by putting excessive numbers of livestock on the range, and they argue that almost half of the range areas in the United States are in dire need of conservation .
Environmentalists argue that it is possible to eliminate overgrazing and manage rangelands in a way that both preserves ecosystems and meets the needs of ranchers. They advocate above all the reduction of herds. They also suggest that cattle should not be allowed to roam at will and should be rotated among various pastures, so that all rangeland areas can receive back-to-back spring and summer rest.
Perhaps the main obstacle in conservation of rangelands is the lack of knowledge regarding their diverse ecosystems. Rangelands are regions where natural revegetation tends to be slow. Artificial attempts to introduce and establish plant growth have been frustrated by the fact that development is a long-term process in these environments as well as by other factors. Knowledge of the dynamics of competition , reaction, and stabilization of species is minimal. For over a century, rangers have tried to eliminate sagebrush, planting wheatgrass in its place. The solution has been short-lived because sagebrush usually prevails over wheatgrass in the natural succession of plants. To further compound the problem, overgrazing has depleted the perennial grasses that compete with sagebrush, and the plant has become even more prolific. A better understanding of the dynamic relationship between plants, animals, microorganisms , soil, and the climate is necessary to reestablish rangeland areas.
[Debra Glidden ]
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