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Grazing
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Grazing generally describes a type of predation in which a herbivore feeds on plants (such as grasses), or more broadly on a multicellular autotrophs (such as kelp). Grazing differs from true predation because the organism being eaten is not killed, and it differs from parasitism as the two organisms do not live together, nor is the grazer necessarily so limited in what it can eat (see generalist and specialist species).
The word "graze" derives from the Old English (OE) grasian, "graze", itself related to OE graes, "grass".
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Encyclopedia
Grazing generally describes a type of predation in which a herbivore feeds on plants (such as grasses), or more broadly on a multicellular autotrophs (such as kelp). Grazing differs from true predation because the organism being eaten is not killed, and it differs from parasitism as the two organisms do not live together, nor is the grazer necessarily so limited in what it can eat (see generalist and specialist species).
The word "graze" derives from the Old English (OE) grasian, "graze", itself related to OE graes, "grass". For terrestrial animals grazing is normally distinguished from browsing in that grazing is eating grass or other low vegetation, and browsing is eating woody twigs and leaves from trees and shrubs . Many small selective herbivores follow larger grazers, who skim off the highest, tough growth of plants exposing tender shoots.
History
United States
The use of livestock grazing can be dated back to the Civil War. During this time land ownership was not widely utilized and ranchers grazed their cattle on the surrounding land, often federal land. Not having a permanent home, these cowboys would frequently graze an area down, and then continue on their way. However, more commonly cattle were rotated between summer and winter ranges. Soon, the public saw how profitable cattle could be and everyone tried to get into the cattle business. With the appearance of free, unlimited grass and feed, the land became overcrowded and the forage rapidly depleted. Ranchers tried to put a stop to this by using barbed wire fences to barricade their land, water sources, and cattle. After failed attempts, the Taylor Grazing Act was enacted in 1934. This act was put into place to help regulate the use of public land for grazing purposes and allotted ranchers certain paddocks of land. Additionally, “fees collected for grazing livestock on public lands was returned to the appropriate grazing district to be used for range improvements”. The Taylor Grazing Act helped to stabilize rancher’s operations and allow them to continue raising their livestock.
Grazing Systems
In the 19th century, grazing techniques were virtually non-existent. Pastures would be grazed for long periods of time, with no rest in between. This led to overgrazing and it was detrimental to the land, wildlife, and livestock producers. Today, ranchers have developed grazing systems to help improve the forage production for livestock, while still being beneficial to the land.
Controlled vs. Continuous
Two major types of grazing management are controlled and continuous. With continuous grazing, the livestock have free selection of forage, while with controlled grazing, the producer regulates forage availability and quality.
Seasonal
Seasonal grazing incorporates “grazing animals on a particular area for only part of the year”. This allows the land that is not being grazed to rest and allow for new forage to grow.
Rotational
Rotational grazing “involves dividing the range into several pastures and then grazing each in sequence throughout the grazing period”. Utilizing rotational grazing can improve livestock distribution while incorporating rest period for new forage.
Rest Rotation
Rest rotation grazing "divides the range into at least four pastures. One pasture remains rested throughout the year and grazing is rotated amongst the residual pastures." This grazing system can be especially beneficial when using sensitive grass that requires time for rest and regrowth.
Deferred Rotation
Deferred rotation “involves at least two pastures with one not grazed until after seed-set”. By using deferred rotation, grasses can achieve maximum growth during the period when no grazing occurs.
Patch Burn Grazing
Patch burn grazing consists of burning a portion of a pasture, while using intensive grazing on the other part throughout the year. This increases new growth and the cattle are attracted to the new grass following the fire.
Riparian Area Grazing Management
Riparian area grazing is used more towards improving wildlife and their habitats. It utilizes fencing to keep livestock off ranges near streams or water areas until after wildlife or waterfowl periods, or limiting the amount of grazing to a short period of time.
Ecological effects
A number of ecological effects derive from grazing, and these may be either positive or negative. Negative effects of grazing (or more usually over-grazing) include increased soil erosion, adverse water quality impacts from increased runoff and loss of biodiversity. For example historical grazing, along with other land consversion, in Northern and Central California has reduced native chaparral and forest lands by approximately 70 percent. Ongoing grazing expansion driven by human population growth in this region threatens the remaining integrity of California montane chaparral habitat in this region.
In some habitats, appropriate levels of grazing may be effective in restoring or maintaining native grass and herb diversity in rangeland that has been disturbed by overgrazing, lack of grazing (such as by the removal of wild grazing animals), or by other human disturbance. Conservation grazing is the use of domestic livestock to manage such habitats, often to replicate the ecological effects of the wild relatives of livestock, or those of other species now absent or extinct. For example, heathland in Europe requires grazing by cattle, sheep or other grazers to maintain its structure and diversity.
Much grazing land has resulted from a process of clearance or drainage of other habitats such as woodland or wetland
Benefits
Production
By utilizing grazing systems, livestock production has the potential to be maximized. “Approximately 85 percent of U.S. grazing lands are unsuitable for producing crops. Grazing animals on this land more than doubles the area that can be used to produce food. Cattle serve a valuable role in the ecosystem by converting the forages humans cannot consume into a nutrient-dense food”. Some could say ranchers themselves are conservationists. They work to use natural resources and often perform tests on their land to analyze soils, control weeds, and utilize smart grazing practices. Through this, they benefit themselves by using profitable land to maximize their livestock production in turn for a profit.
Environmental
Although it’s often forgotten, grazing is very beneficial to the ecosystem. It is advantageous towards the soil and grasses, promoting nutrient dense soil and stimulating the growth of plant varieties. Through grazing, livestock encourages plant growth, consequently increasing forage production. Furthermore, the animal’s urine and feces "recycle nitrogen, phosphorus, potassium and other plant nutrients and return them to the soil". It also acts as rations for insects and organisms found within the soil. These organisms “aid in carbon sequestration and water filtration”. Nutrients and organisms, all of which are necessary for soil to be prosperous and capable for production.
Grazing also helps to promote the growth of native plants and grasses. Often, these indigenous plants aren’t able to compete with the surrounding plants that utilize the majority of water and nutrients. By livestock grazing, the non-native grasses are controlled and the native plants can redevelop. As well as using grazing to increase plant growth, the actual hoof action of the livestock also promotes growth. The trampling helps to imbed the seeds into the soil so that the plants and grasses can continue to germinate.
Additionally, management in many parks makes use of grazing to help lower fire hazards by reducing the amount of potential fuel, such as large buildups of forage. When the land is not grazed, dead grasses accumulate. These dead grasses are often a large fire hazard in the summer months. On the other hand, grazing can also allow for "accumulation of litter (horizontal residue)" helping to eliminate soil erosion. Soil erosion is important to minimize because with the soil erosion comes a loss of nutrients and the topsoil. All of which are important in the regrowth of vegetation.
Biodiversity
Grazing may also promote biodiversity. Many species are dependant on ranch lands and grazing animals to maintain their habitat. The grasses that are stimulated through grazing provide a habitat for many species. When the land is left unattended or is not grazed, grasses will die with the seasons and accumulate as litter on the ground. For many birds, this is not attractive and they avoid making a nesting area of it. However, when the grass is grazed, the dead litter grass is reduced and allows for the birds to utilize it, while at the same time the livestock benefit. Just as importantly, it increases species richness. When grazing is not used, many of the same grasses grow, for example, brome and bluegrass, consequently creating a monoculture.
In North American tallgrass prairies, diversity and productivity are controlled to a large extent by nitrogen availability…Nitrogen availability in prairies was driven by interactions between frequency of fires and grazing by large herbivores…Spring fires enhance growth of certain grasses, and herbivores such as bison preferentially graze these grasses, keeping a system of checks and balances working properly, and allowing many plant species to flourish.
Disadvantages
Although livestock grazing can be very beneficial to the ecosystem and biodiversity through proper management techniques, it can also be damaging. Misuse of the range and lack of education can potentially lead to harmful effects.
Environmental
Grazing can cause disorder to the natural chemical processes of the soil, while at the same time, causing erosion to soil. “Livestock grazing is the most widespread land management practice in western North America. Seventy percent of the western United states is grazed…”. However, overgrazing, when not properly managed is often a problem. Grazing, in general, affects the ecosystem, disrupting both physical characteristics and the surrounding species population. Overgrazing can lead to a decreased forage yield, which correlates to lower quality forage. In addition, the lack of ground cover causes the top soil to be more susceptible to erosion and increased weed production. Problems associated with grazing is not only throughout the grasslands, but also near vegetative riparian areas. These areas are usually wetlands, near streams, that contain high amounts of vegetation. The vegetation is binded to the soil to help prevent erosion and runoff during rainfall, however when livestock grazing takes place on or near these areas it causes “shifts in the plant community structure and removal of plant growth or biomass”. This leads to more dilemmas with sediment loss and temperature change.
"Livestock grazing riparian areas can increase sediment load from the watershed, increase instream trampling,
increase disturbance and erosion from overgrazed streambanks, reduced sediment trapping by riparian and instream vegetation,
decreased bank stability and increased peak flows from compaction."
When the livestock graze close to the streams, their trampling causes and increase in sediment and also interferes with the natural morphology of the stream. The added sediment in the ponds causes the depth to decrease, therefore disturbing the species occupying the pond. Also, without the vegetation, the temperature can change. Even a slight change in the temperature of the habitat can cause effects on the fish and other species.
Biodiversity
It is obvious that without proper land and grazing management practices the ecosystem can be damaged, as well as biodiversity. Looking further into the harmful effects on biodiversity, it is shown that species can suffer as well. Grazing interrupts a species’ natural habitat, just as exposed with grazing and its effects on fish. Many species live in the tall grass,’ so a disruption in their ecosystem can cause a decrease in the species’ density and richness. With the loss of habitat, species are at a greater risk for predation and a lesser food supply. Additionally, with the land being grazed, the species that have occupied the land for years are now being forced to compete with livestock for forage. “The decline in prairie-dog numbers, the second most significant herbivore on the Great Plains, is estimated to be 98% since European settlement (Marsh 1984). This decline has been attributed to potential competition between prairie dogs and cattle for grass forage…”.
Non-grass grazing
Grazing is typically associated with mammals feeding on grasslands, or more specifically livestock in a pasture. However, ecologists sometimes use the word by extension in a broader sense, to include any organism that feeds on any other species without ending the life of the prey organism. An example of a grazer that may seem counterintuitive is a mosquito, which is not a parasite in that it does not form any lasting association with its prey, and is not a true predator in that it does not kill them by this process (although they can act as a vector for fatal diseases such as malaria). In this sense it is the antithesis of parasitoidism, in which an organism (typically the larval stage of a wasp) feeds on another by eating it from within. In that case, the prey is inevitably killed by predation, and has an intimate association with its predator, such that its premature death would also see the parasitoid die as well. Use of the term varies however, for example a marine biologist may describe herbivorous sea urchins that feed on kelp as grazers, even when they kill the organism by cutting the plant at the base.
Grazing Management
It is apparent that proper land and grazing management techniques need to be utilized to optimize forage production and livestock production, while still maintaining biodiversity and consideration of the ecosystem. Through the utilization of grazing systems and making sure to allow proper recovery periods for regrowth, both the livestock and ecosystem will benefit. Along with recovery periods, producers can keep a low density on a pasture, so as not to overgraze. Controlled burning of the land can be valuable in the regrowth of indigenous plants, and new lush growth. Additionally, producers can increase plant and species richness through grazing, by providing an adequate habitat. Although grazing can be problematic for the ecosystem at times, it is clear that smart grazing techniques can reverse damage and improve the land.
See also
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