Grazing pressure
Grazing pressure is defined as the number of grazing animals of a specified class (age, species, physiological status like pregnant) per unit weight of herbage (herbage biomass). It is well established in general usage. [1]
Definition
Grazing pressure is the demand for feed from
Livestock grazing pressure
Grazing pressure due to livestock can be regulated and controlled more easily compared to that from native and feral animals.[3] Rather than use open fields for grazing among domestic animals, cereal pastures may be used as an alternative. This reduces the grazing pressure on local shrublands. In areas of the
Within the environment
On land
Disturbance of plant life caused by the grazing of large
Some studies suggest grazing may be beneficial in nutrient-rich conditions and harmful in habitats poor in nutrients. In other cases grazing will not affect ecosystems whatsoever. For instance, in the Mongolian rain forest, Cheng et al. have found that grazing pressure plays a highly, positive important role in species richness in the wetter steppe of the rain forest. The same research has found that in the dryer, desert ecosystem grazing pressure did not affect species richness significantly.[7] Introductions of new types of grazing pressure can change ecosystems if the plants are not adapted to it.
In a study performed by Saccone et al., when experimenting with biodiversity in the Fennoscandia tundra, they found that there was an increase in species richness associated with decrease of shrub cover.[6] It was shown that in the Fennoscandia tundra grazing is an important and efficient biotic filter restricting the spread of dwarf shrubs to mountain tundra snowbeds. In other words, because of grazing and fewer shrubs, there was more biodiversity among the species.
There are mechanisms that plants use to defend themselves against the grazing pressure of herbivores. Carbon-based secondary
In water
In the ocean, grazing pressure tends to increase with decreasing latitude.
Kelp in coastal water shelters the water column from UV radiation and protects the coasts from waves and storms. Grazing pressure can decrease this protection and shelter. For example, the kelp
In a study produced by Rothausler et al.,[9] kelps that were not exposed to UV radiation were consumed more by grazers than those kelps that were exposed to UV radiation.
On a microbial level
While grazing pressure is more commonly thought in larger herbivores such as cattle, geese, and goats, it is also found within bacterium and on a more microbial level. Leaf-litter colonizing bacteria are a type of bacterium that have been studied regarding grazing pressure on a smaller scale. While it seems that grazing pressure in such a localized environment would not have any large effects, one study found the opposite. Conducted in 2014, researchers found that when they added nitrogen and phosphorus, as well as increased the temperature, it increased the density of the bacteria within a freshwater environment. While this was a controlled experiment, there are real life consequences that should be considered as global warming becomes a greater issue. If the populations of bacteria increase enough then it is possible that the grazing pressure will reach a detrimental level. Once it reaches this peak, the bacteria will have depleted their food resources and may perhaps cause a collapse within the environmental food chain in that area.[10]
Another negative effect caused by grazing pressure was found in
Mitigation
The native kangaroo population in Australia is kept under control by hunters. This helps to contain the grazing pressure level while turning a profit for locals. Hunters must abide by a quota set by the Australian federal government. Kangaroo hunting is an effective control method in open areas but are less effective in dense areas where human accessibility is limited. While effective in the native kangaroo population, shooting is not effective within the goat population where herds are much larger. Instead, large herds are mustered together by a plane or trapped.[12] Trapping is illegal within the kangaroo population.
Another method of population control is limiting the water in the area. Australian governments have been known to cap bores or troughs in order to get feral kangaroos or goats to move on. Some farmers have created kangaroo-proof fences with swing or trap gates that allows cattle and sheep in but keeps other animals out. These fences protect water sources and pastures, forcing kangaroos to move on elsewhere for resources. One problem with this method of reducing grazing pressure in one area, is simply pushing the problem on neighboring pastures and croplands.
In other areas of the world, such as Europe, where rising goose levels are becoming a problem for local agricultural pastures, other ideas have been contemplated. It was proposed that by managing nature reserves in the area, this might help decrease the negative effect of grazing pressure on farmland. By increasing the number of geese that can make use of the native flora on the reserves, this will cut costs for the crops lost to geese grazing on farmlands.[13]
References
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- ^ Business Queensland, Queensland Govt (July 2013). "Total grazing pressure". Grazing and Pasture Management. Queensland Govt. Retrieved 15 September 2018.
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- ^ "Managing Total Grazing Pressure" (PDF).
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- Vallentine, J.F. 2001. Grazing Management, 2nd ed. Academic Press. pp. 383–384.