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Overgrazing

Overgrazed area in western New South Wales (Australia), by loss of native flora, in the upper right corner
Satellite image of the border between Israel and Egypt. The Egyptian side, to the left, is overgrazed.
Penned goats in an overgrazed landscape (Norte Chico, Chile)
Huge herd of migratory wildebeest in Masai Mara during their annual migration shows landscape not 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.

Overgrazing 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. Degrading land, emissions from animal agriculture and reducing the biomass in a ecosystem contribute directly to climate change[2] between grazing events. Successful planned grazing strategies have been in support of the American bison of the Great Plains,[3][4] or migratory wildebeest of the African savannas,[5] or by holistic planned grazing.[6]

Ecological impact

Overgrazing typically increases soil erosion.[7]

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.[8]

Native plant grass species, both individual bunch grasses and in grasslands, are especially vulnerable. For example, excessive browsing by white-tailed deer can lead to the growth of less preferred species of grasses and ferns or non-native plant species[9] that can potentially displace native, woody plants, decreasing the biodiversity.[10][11]

Turning to the aquatic environment, Ling et al. (2015)[12] have documented the phenomenon of catastrophic sea urchin overgrazing and its role in marine ecosystem regime shifts. Their study underscores the urgent need for effective management and conservation strategies to mitigate the profound ecological impacts of overgrazing, highlighting the issue's global scope. Similarly, on the Mongolian steppes, Liu et al. (2013)[13] found that approximately 60% of vegetation decline could be attributed to climate factors, with the rest significantly influenced by increased goat density due to overgrazing. This points to a complex interplay between climate change and grazing practices in ecosystem degradation.

Further expanding our understanding, Stevens et al. (2016)[14] investigated woody encroachment in South African savannahs over a 70-year period, identifying overgrazing, global changes, and the ecological effects of megafauna extinction as key factors. Their findings shed light on the multifaceted drivers behind changes in savannah ecosystems. Echoing this theme of alternative strategies to combat overgrazing, Kriegisch et al. (2019)[15] demonstrated how drift-kelp availability could reduce the foraging movement of overgrazing sea urchins, suggesting that alternative food sources may significantly influence grazing behaviors and aid in managing marine ecosystem pressures.

In a similar vein, the research by Cai et al. (2020)[16] presents a stark example of the terrestrial impact of overgrazing, showing how the fertile island effect collapses under extreme conditions in shrub-encroached grasslands. This case study emphasizes the critical need for sustainable grazing practices to protect soil health and maintain ecosystem functionality, further illustrating the wide-reaching consequences of overgrazing across diverse habitats.

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.[17] This cited the work of a Victorian economist who used as an example the over-grazing of common land. 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.[18] In reality the use of common land in England and Wales was a triumph of conserving a scarce resource using agreed custom and practice.

By region

Africa-Sahel region

There have been overgrazing consequences in the region 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.[19][20] See 2010 Sahel famine.

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 woody plant encroachment at the expenses of grasses on a land area of up to 45 million hectares.

Australia

In many arid zones in Australia, overgrazing by sheep and cattle during the 19th century, as pastoralism was introduced by European settlers, caused many long-lived species of trees and shrubs to give way to short-lived annual plants and weed species. Introduced feral rabbits, cats and foxes exacerbated the threat to both flora and fauna. Many bird species have become extinct or endangered, and many of the medium-sized desert mammals are now completely extinct or only exist on a few islands of Australia.[21]

Overgrazing can also occur with native species. In the Australian Capital Territory, the local government in 2013 authorised a cull of 1455 kangaroos due to overgrazing.[22] Maisie Carr (1912-1988), Ecologist and Botanist, undertook significant research and studies in overgrazing and established consequences on the surrounding land in Australia.

Caribbean

In the Caribbean region, overgrazing is a threat to vegetation areas where there is livestock farming, which is an important source of livelihood and food security for many people. a combination of small scale livestock farming with small ruminants, and mixed farming is practised. However, livestock consume vegetation faster than it can be renewed and this leads to land degradation, loss of vegetative areas, and soil erosion resulting in poor quality feed and reduced livestock yields and income. Also, these grazing lands are critical in controlling carbon dioxide and mitigating risks against severe weather such as floods and droughts. Overgrazing weakens ecological conservation.[23]

New Zealand

In New Zealand, overgrazing is a massive threat to the native species of flora and fauna, especially the native bushes which are often overlooked by invasive species looking for homes.[citation needed] Mustalids, rabbits, hares and possums often eat the plants that hold soil together. This makes the ground very unstable and crumbly. If soil is unstable, it is prone to collapse in extreme weather events such as floods and heavy rain. This is detrimental to farmers of crops and animals alike. 40% of the native species of New Zealand have been wiped out by pests including humans.[citation needed]

See also

References

  1. ^ Mysterud, Atle (2006). "The concept of overgrazing and its role in management of large herbivores". Wildlife Biology. 12 (2): 129–141. doi:10.2981/0909-6396(2006)12[129:TCOOAI]2.0.CO;2. ISSN 0909-6396. S2CID 55599448.
  2. ^ "The relationship between overgrazing and the US environment". ArcGIS StoryMaps. 13 March 2020. Retrieved 2021-03-20.
  3. ^ 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.
  4. ^ 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.
  5. ^ In balance with, and accompanied by, prides of keystone predators.
  6. ^ "Holistic Land Management: Key to Global Stability" by Terry Waghorn. Forbes. 20 December 2012.
  7. ^ C. Michael Hogan (2009). "Overgrazing" (Archived 2010-07-11 at the Wayback Machine). Encyclopedia of Earth. Sidney Draggan, topic ed.; Cutler J. Cleveland, ed. Washington, D.C.: National Council for Science and the Environment.
  8. ^ 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.
  9. ^ 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.
  10. ^ 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.
  11. ^ Horsley, S. B., Stout, S. L., & DeCalesta, D. S. (2003). White‐tailed deer impact on the vegetation dynamics of a northern hardwood forest. Ecological applications, 13(1), 98-118.
  12. ^ Ling, S. D.; Scheibling, R. E.; Rassweiler, A.; Johnson, C. R.; Shears, N.; Connell, S. D.; Salomon, A. K.; Norderhaug, K. M.; Pérez-Matus, A.; Hernández, J. C.; Clemente, S.; Blamey, L. K.; Hereu, B.; Ballesteros, E.; Sala, E. (2015-01-05). "Global regime shift dynamics of catastrophic sea urchin overgrazing". Philosophical Transactions of the Royal Society B: Biological Sciences. 370 (1659): 20130269. doi:10.1098/rstb.2013.0269. ISSN 0962-8436. PMC 4247405.
  13. ^ Liu, Yi Y.; Evans, Jason P.; McCabe, Matthew F.; Jeu, Richard A. M. de; Dijk, Albert I. J. M. van; Dolman, Albertus J.; Saizen, Izuru (2013-02-25). "Changing Climate and Overgrazing Are Decimating Mongolian Steppes". PLOS ONE. 8 (2): e57599. Bibcode:2013PLoSO...857599L. doi:10.1371/journal.pone.0057599. ISSN 1932-6203. PMC 3581472. PMID 23451249.
  14. ^ Stevens, Nicola; Erasmus, B. F. N.; Archibald, S.; Bond, W. J. (2016-09-19). "Woody encroachment over 70 years in South African savannahs: overgrazing, global change or extinction aftershock?". Philosophical Transactions of the Royal Society B: Biological Sciences. 371 (1703): 20150437. doi:10.1098/rstb.2015.0437. ISSN 0962-8436. PMC 4978877. PMID 27502384.
  15. ^ Kriegisch, N.; Reeves, S. E.; Flukes, E. B.; Johnson, C. R.; Ling, S. D. (2019-07-01). "Drift-kelp suppresses foraging movement of overgrazing sea urchins". Oecologia. 190 (3): 665–677. Bibcode:2019Oecol.190..665K. doi:10.1007/s00442-019-04445-6. ISSN 1432-1939. PMID 31250188.
  16. ^ Cai, Yurong; Yan, Yuchun; Xu, Dawei; Xu, Xingliang; Wang, Chu; Wang, Xu; Chen, Jinqiang; Xin, Xiaoping; Eldridge, David J. (2020-03-01). "The fertile island effect collapses under extreme overgrazing: evidence from a shrub-encroached grassland". Plant and Soil. 448 (1): 201–212. Bibcode:2020PlSoi.448..201C. doi:10.1007/s11104-020-04426-2. ISSN 1573-5036.
  17. ^ Garrett Hardin (December 13, 1968), "The Tragedy of the Commons", Science, Vol. 162, No. 3859, pp. 1243-1248. Also available here and here.
  18. ^ Susan Jane Buck Cox (Spring 1985). "No Tragedy on the Commons". Journal of Environmental Ethics, Vol. 7.
  19. ^ "The Deadliest Conflict You've Never Heard of". Foreign Policy. 23 January 2019.
  20. ^ "The battle on the frontline of climate change in Mali". BBC News. 22 January 2019.
  21. ^ "Arid Recovery – Roxby Downs, South Australia". EMR Project Summaries. 15 March 2016. Retrieved 27 October 2020.
  22. ^ "ACT Territory and Municipal Services Directorate | Media Releases Kangaroo conservation cull to go ahead". ACT Territory and Municipal Services Directorate. Government of the Australian Capital Territory. 2013-07-10. Archived from the original on 2020-07-02. Retrieved 2021-06-12.
  23. ^ "Caribbean Islands - Threats | CEPF". www.cepf.net. Retrieved 2024-04-08.

Further reading

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Overgrazing
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