Overgrazing

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Overgrazed area, by native fauna in western New South Wales (Australia), in the upper right corner. Overgrazing.JPG
Overgrazed area, by native fauna in western New South Wales (Australia), in the upper right corner.
Satellite image of the border between Israel and Egypt. The Egyptian side, to the left, is overgrazed Israel Egypt Border.JPG
Satellite image of the border between Israel and Egypt. The Egyptian side, to the left, is overgrazed

Overgrazing occurs when plants are exposed to intensive grazing for extended periods of time, or without sufficient recovery periods. [1] It can be caused by either livestock in poorly managed agricultural applications, game reserves, or nature reserves. It can also be caused by immobile, travel restricted populations of native or non-native wild animals. However, "overgrazing" is a controversial concept, based on equilibrium system theory. A strong indicator of overgrazing is where additional feed needs to be brought in from outside the farm, often to support livestock through the winter. Traditionally this feed was sourced on the farm, with fewer animals being kept and some fields being used for hay and silage production. Modern farm businesses often choose to keep more animals than their land can support alone; buying in external feed to offset this.

Contents

It reduces the usefulness, productivity, and biodiversity of the land and is one cause of desertification and erosion. Overgrazing is also seen as a cause of the spread of invasive species of non-native plants and of weeds. It is reversed or prevented by moving grazers in large herds, such as the American bison of the Great Plains, [2] [3] or migratory Wildebeests of the African savannas, [4] or by holistic planned grazing. [5]

Preventing overgrazing

Preventing Man-made Overgrazing
Cabrasnortechico.JPG
Immobilized goat herd inside of a pen in an overgrazed habitation of Norte Chico, Chile
Wildebeest-during-Great-Migration.JPG
Huge herd of migratory Wildebeest in Masai Mara during the Great Migration

Sustainable grassland production is based on grass and grassland management, land management, animal management and livestock marketing. Grazing management, with sustainable agriculture and agroecology practices, is the foundation of grassland-based livestock production, since it affects both animal and plant health and productivity. There are several new grazing models and management systems that attempt to reduce or eliminate overgrazing like Holistic management [6] [7] and Permaculture [8] [5]

Indicators

One indicator of overgrazing is that the animals run short of pasture. In some regions of the United States under continuous grazing, overgrazed pastures are predominated by short-grass species such as bluegrass and will be less than 2-3 inches tall in the grazed areas. In other parts of the world, overgrazed pasture is typically taller than sustainably grazed pasture, with grass heights typically over 1 meter and dominated by unpalatable species such as Aristida or Imperata . In all cases, palatable tall grasses such as orchard grass are sparse or non-existent. In such cases of overgrazing, soil may be visible between plants in the stand, allowing erosion to occur, though in many circumstances overgrazed pastures have a greater sward cover than sustainably grazed pastures.

Rotational grazing

Under rotational grazing, overgrazed plants do not have enough time to recover to the proper height between grazing events. The animals resume grazing before the plants have restored carbohydrate reserves and grown back roots lost after the last defoliation. The result is the same as under continuous grazing: in some parts of the United States tall-growing species die and short-growing species that are more subject to drought injury predominate the pasture, while in most other parts of the world tall, drought tolerant, unpalatable species such as Imperata or Aristida come to dominate. As the sod thins, weeds encroach into the pasture in some parts of the United States, whereas in most other parts of the world overgrazing can promote thick swards of native unpalatable grasses that hamper the spread of weeds.

Another indicator of overgrazing in some parts of North America is that livestock run out of pasture, and hay needs to be fed early in the fall. In contrast, most areas of the world do not experience the same climatic regime as the continental United States and hay feeding is rarely conducted.

Overgrazing is also indicated in livestock performance and condition. Cows having inadequate pasture immediately following their calf's weaning may have poor body condition the following season. This may reduce the health and vigor of cows and calves at calving. Also, cows in poor body condition do not cycle as soon after calving, which can result in delayed breeding and a long calving season. With good cow genetics, nutrition, ideal seasons and controlled breeding 55% to 75% of the calves should come in the first 21 days of the calving season. Poor weaning weights of calves can be caused by insufficient pasture, when cows give less milk and the calves need pasture to maintain weight gain.

Ecological impacts

Overgrazing typically increases soil erosion. [9] Reduction in soil depth, soil organic matter and soil fertility impair the land's future natural and agricultural productivity. Soil fertility can sometimes be mitigated by applying the appropriate lime and organic fertilizers. However, the loss of soil depth and organic matter takes centuries to correct. Their loss is critical in determining the soil's water-holding capacity and how well pasture plants do during dry weather.

Overgrazing results in increased trampling of soil by livestock, which increases soil compaction (Fuls, 1992) and thus, decreases the permeability of the soil. Furthermore, with more exposure of soil due to the decrease in plant biomass, the soil is exposed to increased levels of direct rainfall, creating a crust layer that is compacted and impermeable. This impermeability is what increases runoff and soil erosion [10] .

With continued overutilization of land for grazing, there is an increase in degradation. This leads to poor soil conditions that only xeric and early successional species can tolerate [11] .

Native plant grass species, both individual bunch grasses and in grasslands, are especially vulnerable. For example, excessive browsing of white-tailed deer can lead to the growth of less preferred species of grasses and ferns or non-native plant species [12] that can potentially displace native, woody plants, decreasing the biodiversity [13] .

North America

In the continental United States, to prevent overgrazing, match the forage supplement to the herd's requirement. This means that a buffer needs to be in the system to adjust for the fastest growth of forages.

Another potential buffer is to plant warm-season perennial grasses such as switchgrass, which do not grow early in the season. This reduces the area that the livestock can use early in the season, making it easier for them to keep up with the cool-season grasses. The animals then use the warm-season grasses during the heat of the summer, and the cool-season grasses recover for fall grazing.

The grazing guidelines in the table are for rotationally grazed, cool-season forages. When using continuous grazing, manage pasture height at one-half the recommended turn-in height for rotational grazing to optimize plant health. The growth habit of some forage species, such as alfalfa, does not permit their survival under continuous grazing. When managing for legumes in the stand, it is beneficial to use rotational grazing and graze the stand close and then give adequate rest to stimulate the legumes' growth.

Economic theory

Overgrazing is used as an example in the economic concept now known as the Tragedy of the Commons devised in a 1968 paper by Garrett Hardin. [14] This cited the work of a Victorian economist who used the over-grazing of common land as an example of behaviour. Hardin's example could only apply to unregulated use of land regarded as a common resource.

Normally, rights of use of Common land in England and Wales were, and still are, closely regulated, and available only to "commoners". If excessive use was made of common land, for example in overgrazing, a common would be "stinted", that is, a limit would be put on the number of animals each commoner was allowed to graze. These regulations were responsive to demographic and economic pressure; thus rather than let a common become degraded, access was restricted even further. This important part of actual historic practice was absent from the economic model of Hardin. [15] In reality the use of common land in England and Wales was a triumph of conserving a scarce resource using agreed custom and practice.

Africa-Sahel region

The violent herder–farmer conflicts in Nigeria, Mali, Sudan and other countries in the Sahel region have been exacerbated by land degradation and overgrazing. [16] [17]

Sub-Sahara Africa

Various countries in Sub-Sahara Africa are affected by overgrazing and resulting ecological effects. In Namibia, overgrazing is considered the main cause of the thickening of shrubs and bushes at the expenses of grassees on a land area of up to 45 million hectares (see bush encroachment).

Australia

Overgrazing does not necessarily mean total denudation of the land. Overgrazing can also occur with native species. In the Australian Capital Territory, Australia the local government, in 2013, authorised the culling of 1455 kangaroos due to overgrazing.

Further reading

See also

Related Research Articles

<i>Onobrychis</i> Genus of flowering plants in the bean family Fabaceae

Onobrychis, the sainfoins, are Eurasian perennial herbs of the legume family (Fabaceae). Including doubtfully distinct species and provisionally accepted taxa, about 150 species are presently known. The Flora Europaea lists 23 species of Onobrychis; the main centre of diversity extends from Central Asia to Iran, with 56 species – 27 of which are endemic – in the latter country alone. O. viciifolia is naturalized throughout many countries in Europe and North America grasslands on calcareous soils.

Savanna Mixed woodland-grassland ecosystem

A savanna or savannah is a mixed woodland-grassland ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach the ground to support an unbroken herbaceous layer consisting primarily of grasses.

Pasture land used for grazing

Pasture land is used for grazing. Pasture lands in the narrow sense are enclosed tracts of farmland, grazed by domesticated livestock, such as horses, cattle, sheep, or swine. The vegetation of tended pasture, forage, consists mainly of grasses, with an interspersion of legumes and other forbs. Pasture is typically grazed throughout the summer, in contrast to meadow which is ungrazed or used for grazing only after being mown to make hay for animal fodder. Pasture in a wider sense additionally includes rangelands, other unenclosed pastoral systems, and land types used by wild animals for grazing or browsing.

Rotational grazing System of grazing moving animals between paddocks around the year

In agriculture, rotational grazing, as opposed to continuous grazing, describes many systems of pasturing, whereby livestock are moved to portions of the pasture, called paddocks, while the other portions rest. Each paddock must provide all the needs of the livestock, such as food, water and sometimes shade and shelter. The approach often produces lower outputs than more intensive animal farming operations, but requires lower inputs, and therefore sometimes produces higher net farm income per animal.

Fodder Agricultural foodstuff used to feed domesticated animals

Fodder, a type of animal feed, is any agricultural foodstuff used specifically to feed domesticated livestock, such as cattle, rabbits, sheep, horses, chickens and pigs. "Fodder" refers particularly to food given to the animals, rather than that which they forage for themselves. Fodder is also called provender and includes hay, straw, silage, compressed and pelleted feeds, oils and mixed rations, and sprouted grains and legumes. Most animal feed is from plants, but some manufacturers add ingredients to processed feeds that are of animal origin.

In agriculture, grazing is a method of animal husbandry whereby domestic livestock are used to convert grass and other forage into meat, milk, wool and other products, often on land unsuitable for arable farming.

Rangeland open grazing land

Rangelands are grasslands, shrublands, woodlands, wetlands, and deserts that are grazed by domestic livestock or wild animals. Types of rangelands include tallgrass and shortgrass prairies, desert grasslands and shrublands, woodlands, savannas, chaparrals, steppes, and tundras. Rangelands do not include forests lacking grazable understory vegetation, barren desert, farmland, or land covered by solid rock, concrete and/or glaciers.

Pastoralism branch of agriculture concerned with raising livestock

Pastoralism is a form of animal husbandry, historically by nomadic people who moved with their herds. The species involved include various herding livestock, including cattle, camels, goats, yaks, llamas, reindeer, horses and sheep.

<i>Pascopyrum</i> genus of plants

Pascopyrum is a monotypic genus of grass containing the sole species Pascopyrum smithii, which is known by the common name western wheatgrass, though the common nickname is red-joint wheatgrass, from the red coloration of the nodes. This is a sod-forming rhizomatous perennial grass which is native and common throughout most of North America. It grows in grassland and prairie in the Great Plains, where it is sometimes the dominant grass species. It is the state grass of North Dakota, South Dakota, and Wyoming.

Pastoral farming covers the systems of production of articles of bovine, type of animal breeding

Pastoral farming is aimed at producing livestock, rather than growing crops. Examples include dairy farming, raising beef cattle, and raising sheep for wool. In contrast, arable farming concentrates on crops rather than livestock. Finally, Mixed farming incorporates livestock and crops on a single farm. Some mixed farmers grow crops purely as fodder for their livestock; some crop farmers grow fodder and sell and in some cases pastoralists. Pastoral farming is a non-nomadic form of pastoralism in which the livestock farmer has some form of ownership of the land used, giving the farmer more economic incentive to improve the land. Unlike other pastoral systems, pastoral farmers are sedentary and do not change locations in search for fresh resources. Rather, pastoral farmers adjust their pastures to fit the needs of their animals. Improvements include drainage, stock tanks, irrigation and sowing clover.

Black-tailed prairie dog species of mammal

The black-tailed prairie dog is a rodent of the family Sciuridae found in the Great Plains of North America from about the United States-Canada border to the United States-Mexico border. Unlike some other prairie dogs, these animals do not truly hibernate. The black-tailed prairie dog can be seen above ground in midwinter. A black-tailed prairie dog town in Texas was reported to cover 25,000 sq mi (64,000 km2) and included 400,000,000 individuals. Prior to habitat destruction, this species may have been the most abundant prairie dog in central North America. This species was one of two described by the Lewis and Clark Expedition in the journals and diaries of their expedition.

Silvopasture

Silvopasture is the practice of integrating trees, forage, and the grazing of domesticated animals in a mutually beneficial way. It utilizes the principles of managed grazing, and it is one of several distinct forms of agroforestry.

<i>Muhlenbergia rigens</i> Species of plant

Muhlenbergia rigens, commonly known as deergrass, is a warm season perennial bunchgrass. It is found in sandy or well-drained soils below 7,000 feet (2,100 m) in elevation in the Southwestern United States and parts of Mexico.

Puna grassland

The Puna grassland ecoregion, of the montane grasslands and shrublands biome, is found in the central Andes Mountains of South America. It is considered one of the eight Natural Regions in Peru, but extends south, across Bolivia, as far as northern Argentina and Chile. The term puna encompasses diverse ecosystems of the high Central Andes above 3200–3400 m.

Conservation grazing Use of animals to graze areas like nature reserves to maintain habitats

Conservation grazing or targeted grazing is the use of semi-feral or domesticated grazing livestock to maintain and increase the biodiversity of natural or semi-natural grasslands, heathlands, wood pasture, wetlands and many other habitats. Conservation grazing is generally less intensive than practices such as prescribed burning, but still needs to be managed to ensure that overgrazing does not occur. The practice has proven to be beneficial in moderation in restoring and maintaining grassland and heathland ecosystems. The optimal level of grazing will depend on the goal of conservation, and different levels of grazing, alongside other conservation practices, can be used to induce the desired results.

Livestock grazing comparison is a method of comparing the numbers and density of livestock grazing in agriculture. Various units of measurement are used, usually based on the grazing equivalent of one adult cow, or in some areas on that of one sheep. Many different schemes exist, giving various values to the grazing effect of different types of animal.

Alpine-steppe

The Alpine-steppe is a high altitude natural alpine grassland, which is a part of the Montane grasslands and shrublands biome.

Range Condition Scoring was developed as a way to quantify biodiversity in a given rangeland system. This practice is widely used in the Sand Hills region of Nebraska, as well as the tallgrass prairie regions, as evidenced by the authoritative book on the subject, "Range Judging Handbook and Contest Guide for Nebraska." This book outlines the steps required to evaluate, or score, a particular region of rangeland; and it serves as a baseline for the understanding of this method of judging rangeland health.

<i>Pennisetum pedicellatum</i> species of plant

Pennisetum pedicellatum, known simply as desho or as desho grass, is an indigenous grass of Ethiopia of the monocot angiosperm plant family Poaceae. It is also known as annual kyasuwa grass in Nigeria, bare in Mauritania, and deenanath grass in India. It grows in its native geographic location, naturally spreading across the escarpment of the Ethiopian highlands. Widely available in this location, it is ideal for livestock feed and can be sustainably cultivated on small plots of land. Thus desho is becoming increasingly utilized, along with various soil and water conservation techniques, as a local method of improving grazing land management and combating a growing productivity problem of the local region.

Holistic management (agriculture) agricultural approach or philosophy

Holistic Management in agriculture is an approach to managing resources that was originally developed by Allan Savory. Holistic Management is a registered trademark of Holistic Management International.

References

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  2. Laduke, Winona (1999). All Our Relations: Native Struggles for Land and Life . Cambridge, MA: South End Press. p.  146. ISBN   0896085996 . Retrieved 30 March 2015.
  3. Duval, Clay. "Bison Conservation: Saving an Ecologically and Culturally Keystone Species" (PDF). Duke University. Archived from the original (PDF) on March 8, 2012. Retrieved April 13, 2015.
  4. In balance with, and accompanied by, prides of keystone predators.
  5. 1 2 "Holistic Land Management: Key to Global Stability" by Terry Waghorn. Forbes. 20 December 2012.
  6. Savory, Allan. "How to green the world's deserts and reverse climate change". youtube.com. TED. Retrieved 14 September 2015.
  7. Savory, Allan. "Can sheep save the planet?". youtube.com. IWTOCHANNEL. Retrieved 14 September 2015.
  8. West Virginia University Extension Service Archived 2009-04-23 at the Wayback Machine Overgrazing Can Hurt Environment, Your Pocketbook Ed Rayburn. 2000.
  9. C.Michael Hogan. 2009. Overgrazing Archived 2010-07-11 at the Wayback Machine . Encyclopedia of Earth. Sidney Draggan, topic ed.; Cutler J. Cleveland, ed., National council for Science and the Environment, Washington DC
  10. Fuls, E.R. (1992). "Ecosystem modification created by patch-overgrazing in semi-arid grassland". Journal of Arid Environments. 23 (1): 59–69. Bibcode:1992JArEn..23...59F. doi:10.1016/S0140-1963(18)30541-X.
  11. Fuls, E.R. (1992). "Ecosystem modification created by patch-overgrazing in semi-arid grassland". Journal of Arid Environments. 23 (1): 59–69. Bibcode:1992JArEn..23...59F. doi:10.1016/S0140-1963(18)30541-X.
  12. Côté, S. D., Rooney, T. P., Tremblay, J. P., Dussault, C., & Waller, D. M. (2004). Ecological impacts of deer overabundance. Annu. Rev. Ecol. Evol. Syst., 35, 113-147.
  13. Baiser, B., Lockwood, J. L., La Puma, D., & Aronson, M. F. (2008). A perfect storm: two ecosystem engineers interact to degrade deciduous forests of New Jersey. Biological Invasions, 10(6), 785-795.
  14. Garrett Hardin, "The Tragedy of the Commons", Science, Vol. 162, No. 3859 (December 13, 1968), pp. 1243-1248. Also available here and here.
  15. Susan Jane Buck Cox - "No tragedy on the Commons" Journal of Environmental Ethics, Vol 7, Spring 1985
  16. "The Deadliest Conflict You've Never Heard of". Foreign Policy . 23 January 2019.
  17. "The battle on the frontline of climate change in Mali". BBC News. 22 January 2019.