Grazing pressure

Grazing pressure is the stress on plant populations due to the grazing of animals. Plants may be lost either directly as a result of animals grazing upon them, or indirectly as a result of damage to the vegetation or ecosystem by animals moving through the area. Usually the term refers to introduced pastoral animals such as cattle and sheep, but in some contexts it may mean introduced feral animals, or even native animals.

Grazing pressure is the demand for feed from herbivores and detritivores within an environment. This could come from domestic animal, such as goats and cattle, feral animals, such as rabbits, and native animals, such as kangaroos or moose. Total grazing pressure reflects the total demand from all herbivores within an environment... Grazing pressure that occurs naturally within an environment is higher than grazing pressure from livestock animals. The predominant dietary component in herbivores diet is grass.

Animals with a high contribution to grazing pressure include cattle, sheep and goats. Grazing pressure within livestock can be regulated and controlled in an easier manner compared to native and feral animals. 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 Mediterranean, both mature goats and their kids were found to have an effect on local shrubbery. Older goats spent about a third of their time grazing in the shrubs, while their young spent at least half their time. The amount of time spent in each type of grazing area also correlated with the genotype of the goat. While the goats were found in the pastures a majority of the time, their grazing patterns still affected local wildlife and shrub growth. Grazing pressure is not only a problem regarding natural grasslands and shrubbery. In northwestern Europe, the rising goose population has caused an increasing in grazing pressure on agricultural lands.

Disturbance of plant life caused by the grazing of large herbivores is an important determinant of plant community structure. Composition of plant and animal species is affected by grazing pressure. Grazing pressure affects plant communities directly through physical removal of the affected plants. It can also affect plant communities indirectly by modulation of ecosystem productivity or by changing the pattern of nutrient partitioning of limiting nutrients among different sizes of plants. Thus, grazing changes the population size, diversity and distribution of organisms in an ecosystem. Grazing pressure strongly affects plant community and composition. Grazing pressure also influences plant species performance and plant ecological stoichiometry. For instance, plant functional composition of tundra is primary structured by grazing pressure.

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