OVERGRAZING: CAUSES, EFFECTS AND SOLUTIONS - ENVIRONMENT - 2025

The overgrazing occurs when herbivores consume a pasture grasses intensively outpacing the ability replenishment of plant material. This is mainly due to an animal load greater than the capacity of the pasture to regenerate.

There are different categories according to the intensity of the overgrazing, referring to it as mild, severe, very severe and destructive. Also, the timescale of overgrazing can be months, years, decades, or even centuries.

Overgrazing by cattle. Source: The original uploader was Ellmist at English Wikipedia. Late versions were uploaded by Minesweeper at en.wikipedia.

Among the effects generated by overgrazing are the drop in productivity in cases of extensive animal production systems. In natural ecosystems, overgrazing causes food deficits, a decrease in herbivore populations and can cause soil degradation, loss of biodiversity and desertification.

It is estimated that there are about 31 million square kilometers affected by overgrazing around the world. The direct solution is to reduce the animal load in the pasture according to its carrying capacity.

Causes

Excess animal load

The dominant plant species in a pasture are grasses, which in these cases are propagated both by seeds and vegetatively. For the latter they use strategies such as the development of stolons, rhizomes or underground basal buds.

The underground structures allow to resist grazing because the herbivore consumes the aerial part of the foliage and the plant regenerates it from these. However, if the number of herbivores is so high that they consume the shoots too quickly, the plant ends up depleting its reserves and dies.

Load capacity and animal load

Carrying capacity refers to the number of herbivores that a pasture is capable of supporting without affecting its regeneration capacity. While the number of herbivorous animals present at a given time in the pasture is called the animal load.

This carrying capacity depends on the animal species, its level and consumption habits, as well as the species of pasture present. Soil fertility and environmental conditions also play a role.

Each animal species has a different impact on the pasture, influencing the way cattle eat. Likewise, the impact of the hooves on the ground and the weight of the animals.

A pasture in a high fertility soil, with highly productive pasture species and in optimal climatic conditions, will support a higher animal load. In contrast, grasslands in arid zones generally support a low animal load.

Decreased animal mobility

The modification of the productive systems and the reduction of the extensions of productive lands concentrate the animal load. For example, ancient transhumant grazing systems involved a rotation of the stock over a large area of ​​land.

Today that animal load must be concentrated in a production unit, increasing animal density.

Overpopulation in natural environments

In the case of natural ecosystems, overgrazing can be caused by a population imbalance. For example, the decrease in the population of predatory carnivores leads to an increase in the population of herbivores that has a greater demand for pastures.

Migrations

Overgrazing by wildlife. Source: Bjørn Christian Tørrissen

By occupying territories, human beings impose restrictions on the natural migrations of herbivores or the extension of land they can cover. This forces these populations to have to be restricted to smaller areas, which causes overgrazing.

Decrease in pasture productivity

Any factor that decreases the primary productivity of the pasture, that is, causes the plants to produce less, contributes to overgrazing. Therefore, if the amount of available grass decreases and the same stock is maintained, overgrazing occurs.

Factors that affect grass growth

There are various factors that can cause a decrease in pasture productivity. Among them is the deficit or excess of water or an increase in the acidity of the soil. They also affect pollutants such as salts, heavy metals and others that are toxic to plants.

Climate change is also a relevant factor, due to global warming, which generates both droughts and floods.

Effects edit

Depending on the intensity of the overgrazing, the final effect is the degradation of the soil with all the consequences that this entails.

Changes in specific composition and loss of biodiversity

Grazing causes changes in the composition of species in the grazed area, due to the selective effect of the process. This occurs because the animal does not always consume everything it finds, being generally selective.

The herbivore consumes those species that are more palatable and therefore those less palatable develop more.

Alien plants and weeds

Overgrazing disrupts the balance of the grassland ecosystem and causes changes in its physical and biological conditions. In this case, species may appear that did not adapt to the original conditions, but in the new conditions they may become invasive.

In the pastures of animal production this can generate the invasion of herbaceous and shrubby weeds.

Biodiversity losses

Overgrazing can cause the extinction of plant species in natural grasslands. On the other hand, it can also lead to a decrease in animal diversity.

For example, some research in grasslands in Oklahoma (United States) shows a decrease in the diversity of rodents and lagomorphs (hares) in overgrazed grasslands.

Decreased productivity

Pasture

Depending on the species, especially its form of growth and vigor, the grass will resist grazing to a greater or lesser extent. If the cutoff frequency is too high, the plant does not have the ability to regenerate and dies.

Pasture deteriorated by overgrazing. Source: Thayne Tuason

On the other hand, other factors derived from overgrazing act that impoverish the soil and therefore restrict the nutrients to the plant. As the soil becomes bare, solar radiation and erosive dragging of water decrease organic matter and fertility.

Animal

The more intense the overgrazing, the more the amount of feed is restricted in relation to the animal load on the ground. This implies a lower caloric intake and therefore a decrease in body weight gain.

Soil compaction

The excess of animal load represents a constant trampling on the ground that ends up compacting it. Compaction causes a decrease in permeability and infiltration, thereby increasing surface runoff and contributing to erosion.

Erosion

The decrease in vegetation cover as a result of overgrazing exposes the soil to inclement weather. The impact of rain, runoff and the effect of the wind will be greater and the erosive effect increases.

Desertification

The loss of vegetation and the subsequent erosion generates a negative spiral of soil degradation that ends in desertification. Globally, 50% of agricultural soils suffer desertification processes that have led to a decrease in the capacity to produce food.

Reduction of carbon sequestration in the soil

The amount of organic matter in the soil and carbon (C) are a function of the balance between primary production and decomposition. Carbon in the soil decreases if the contribution is reduced due to the decrease in primary production due to overgrazing.

Economic losses

The decrease in the productivity of production units caused by overgrazing implies great economic losses. Valuable productive land can be rendered useless and expensive farm animals are lost or underweight.

Social decline

The economic and environmental deterioration that derives from overgrazing brings serious social problems as a consequence. The quality of life in overgrazed areas decreases and even the migration of their populations is pushed.

Solutions

The solution to the problem of overgrazing implies a comprehensive approach that aims to achieve a balance between animal demand and pasture growth.

Adequate animal load

In production units, it is essential to establish the carrying capacity of the pasture to define the appropriate number of animals. This in turn depends on the type of grass present and the management of the production unit.

Energy substitution

Contributions from outside the production unit help to avoid overgrazing. These contributions include the supply of food supplements to the animals, either with concentrated feed or silage.

Establish rest or fallow periods

Pasture rotation is an adequate strategy to reduce pressure on the pasture and thus allow its recovery. This consists of dividing the pasture into lots (paddocks) and defining periods of permanence of the cattle in each one.

These periods are established according to the rate of consumption of the animals and the recovery capacity of the pasture.

The temporary overgrazing designed

Technologies related to rotational, delayed rotational and fallow rotational grazing systems include periods of temporary overgrazing. Overgrazing with sheep and goats can also be used for weed control.

Introduce more productive pastures

Like any living organism, each species of grass is better adapted to certain environmental conditions. That is why special attention must be paid to the selection of the species to be cultivated when creating animal production systems.

The selection must be made according to both the soil conditions, climate and water availability, as well as the type of livestock to be produced.

Improve pasture conditions

In traditional systems of extensive animal production in natural grasslands, human intervention is scarce, beyond the introduced animal load. Under these conditions the risks of overgrazing are greater than in systems with higher technology.

One way to reduce the risks of overgrazing is to improve pasture conditions. For this, it is necessary to influence the different factors that affect pasture productivity, mainly soil fertility and water requirements.

Fertilization

Through a program of incorporation of fertilizers into the soil, it helps to increase the regeneration capacity of the pasture. Organic fertilizers or artificial formulas, especially those rich in nitrogen, can be applied and combined with paddock rotation.

Irrigation

The supply of water, especially in areas with a semi-arid or arid climate, is decisive for maintaining pasture productivity.

Pest control

The grazing pressure on the pasture does not come only from the production animals, there are other herbivores that participate. In this case, they are wild animals that feed on grass and are considered pests in the production system.

The control of herbivores pests (rodents, insects) is an important element to reduce the pressure on the grassland and allow its adequate regeneration.

Production system

A drastic way to eliminate the risk of overgrazing is to discard grazing as a form of production. This consists of establishing an intensive production system with stabled animals (confined in stables) and supplying concentrated feed.

Monitoring and control of ecological balance

In natural grasslands, cases of overgrazing occur due to ecological imbalances of both natural and anthropic origin. In this case, the decisive factor is to control this balance and reduce risk factors.

Population management

In some nature reserves, controlled hunting or the transfer of animals is established to reduce the animal load in a given area.

Overgrazing in Mexico

Overgrazing is a serious problem in Mexico, where 60% of the territory has arid or semi-arid climates. On the other hand, in this country 80% of agricultural lands are threatened by degradation and desertification.

The grazing herd (cows, goats, sheep and pigs) went from 22 million head in 1950 to almost 70 million in 2015. Thus, the grazing pressure is 2-6 times higher than recommended and it is estimated that 24% of the livestock area in the country is affected by overgrazing.

The Mexican Northeast

One of the areas most affected by overgrazing is the northeast of Mexico, mainly due to goat farming. In this case, it is the extensive breeding of goats in the thorny thicket of Tamaulipas.

Overgrazing in Argentina

Argentina is a country with a strong cattle tradition, both in the production of cattle and sheep, being the fundamental base of its economy. One of the largest producing areas is the pampas in Patagonia with around 80,000,000 hectares.

Overgrazing by sheep. Source: I, Ruud Zwart

In this region of Argentina there are serious overgrazing problems, especially caused by sheep that have caused desertification. This is because extensive livestock systems established more than a century ago did not contemplate the sustainable use of natural grasslands.

Overgrazing in Chubut

Chubut is a province of Patagonia in Argentina whose main economic source has been sheep production for more than 100 years. Here sheep overgrazing has caused a reduction of about 90% of the vegetation cover in the semi-arid ecosystems of the west.

The changes generated by overgrazing include the disappearance of species preferred by sheep. Due to this, areas exposed to environmental stress were generated that were invaded by species not palatable to sheep (hard-leaved shrubs).

Overgrazing in Peru

A typical livestock system in Peru is the breeding of the alpaca (Vicugna pacos) for the production of meat and animal fiber. An alpaca population of about 400 thousand animals is estimated that live in semi-arid high mountain climates.

Overgrazing by alpaca (Peru). Source: Philippe Lavoie

According to studies by the Rural Agricultural Productive Development Program (Agro Rural) there is only availability of pastures to feed 20% of this animal population. The animal load is approximately 3 alpacas per hectare of pasture, with the carrying capacity of one alpaca per hectare.

This leads to overgrazing, affecting the quality of the meat and fiber of the animal, with serious economic losses.

Degradation of Andean mountain ecosystems

Andean high mountain ecosystems are one of the areas most threatened by degradation due to overgrazing. This is due to the fact that the factors common to any area, here are the high slope relief and high rainfall.

Overgrazing in protected areas

Eighteen national protected areas have problems of overgrazing, both by cattle and sheep, as well as by alpacas. An example of this is overgrazing in the upper parts of the Huascarán National Park, where cattle and sheep cause serious damage.

References

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