Grassland

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Grassland in Magallanes Region, Patagonia, Chile.
Grassland in the Antelope Valley, California
The Konza tallgrass prairie in the Flint Hills of northeastern Kansas.
A grassland in the Philippines.

Grasslands are areas where the vegetation is dominated by grasses (Poaceae), however sedge (Cyperaceae) and rush (Juncaceae) families can also be found. Grasslands occur naturally on all continents except Antarctica. Grasslands are found in most ecoregions of the Earth. For example there are five terrestrial ecoregion classifications (subdivisions) of the temperate grasslands, savannas, and shrublands biome ('ecosystem'), which is one of eight terrestrial ecozones of the Earth's surface.

Vegetation

Grassland vegetation can vary in height from very short, as in chalk where the vegetation may be less than 30 cm (12 in) high, to quite tall, as in the case of North American tallgrass prairie, South American grasslands and African savanna.

Woody plants, shrubs or trees, may occur on some grasslands – forming savannas, scrubby grassland or semi-wooded grassland, such as the African savannas or the Iberian dehesa. Such grasslands are sometimes referred to as wood-pasture or woodland.[1]

As flowering plants, grasses grow in great concentrations in climates where annual rainfall ranges between 500 and 900 mm (20 and 35 in).[2] The root systems of perennial grasses and forbs form complex mats that hold the soil in place.

Evolution

Graminoids are among the most versatile life forms. They became widespread toward the end of the Cretaceous period, and fossilized dinosaur dung (coprolites) have been found containing phytoliths of a variety of grasses that include grasses that are related to modern rice and bamboo.[3]

The appearance of mountains in the western United States during the Miocene and Pliocene epochs, a period of some 25 million years, created a continental climate favorable to the evolution of grasslands. Existing forest biomes declined, and grasslands became much more widespread. Following the Pleistocene Ice Ages, grasslands expanded in range in the hotter, drier climates, and began to become the dominant land feature worldwide.[1]

Climate

Grasslands often occur in areas with annual precipitation between 600 mm (24 in) and 1,500 mm (59 in) and average mean annual temperatures ranges from −5 and 20 °C (Woodward et al. 2004). However, some grasslands occur in colder(-20°C) and hotter(30°C) climatic conditions.[4] Grassland can exist in habitats that are frequently disturbed by grazing or fire, as such disturbance prevents the encroachment of woody species. Species richness is particularly high in grasslands of low soil fertility such as serpentine barrens and calcareous grasslands. Infertility may also prevent woody encroachment as low nutrient levels in the soil may inhibit the growth of forest and shrub species.most plants from growing. Temperate grasslands occur in temperate climates typified by distinct seasonality (warm summers and cold winters).

Biodiversity and conservation

Grasslands dominated by unsown wild-plant communities ("unimproved grasslands") can be called either natural or 'semi-natural' habitats. The majority of grasslands in temperate climates are 'semi-natural'. Although their plant communities are natural, their maintenance depends upon anthropogenic activities such as low-intensity farming, which maintains these grasslands through grazing and cutting regimes. These grasslands contain many species of wild plants – grasses, sedges, rushes and herbs – 25 or more speerican prairie grasslands or lowland wildflower meadows in the UK are now rare and their associated wild flora equally threatened. Associated with the wild-plant diversity of the "unimproved" grasslands is usually a rich invertebrate fauna; also there are many species of birds that are grassland "specialists", such as the snipe and the Great Bustard. Agriculturally improved grasslands, which dominate modern intensive agricultural landscapes, are usually poor in wild plant species due to the original diversity of plants having been destroyed by cultivation, the original wild-plant communities having been replaced by sown monocultures of cultivated varieties of grasses and clovers, such as Perennial ryegrass and White Clover. In many parts of the world "unimproved" grasslands are one of the least threatened habitats, and a target for acquisition by wildlife conservation groups or for special grants to landowners who are encouraged to manage them appropriately.

Human impact and economic importance

Grassland in Cantabria, northern Spain.
A restored grassland ecosystem at Morton Arboretum in Illinois.

Grasslands are of vital importance for raising livestock for human consumption and for milk and other dairy products.

Grassland vegetation remains dominant in a particular area usually due to grazing, cutting, or natural or manmade fires, all discouraging colonisation by and survival of tree and shrub seedlings. Some of the world's largest expanses of grassland are found in African savanna, and these are maintained by wild herbivores as well as by nomadic pastoralists and their cattle, sheep or goats.

Grasslands may occur naturally or as the result of human activity. Grasslands created and maintained by human activity are called anthropogenic grasslands. Hunting peoples around the world often set regular fires to maintain and extend grasslands, and prevent fire-intolerant trees and shrubs from taking hold. The tallgrass prairies in the US Midwest may have been extended eastward into Illinois, Indiana, and Ohio by human agency. Much grassland in northwest Europe developed after the Neolithic Period, when people gradually cleared the forest to create areas for raising their livestock.

Types ( biomes )

Tropical and subtropical

These grasslands are classified with tropical and subtropical savannas and shrublands as the tropical and subtropical grasslands, savannas, and shrublands biome. Notable tropical and subtropical grasslands include the Llanos grasslands of northern South America.

Temperate

Mid-latitude grasslands, including the Prairie and Pacific Grasslands of North America, the Pampas of Argentina, Brazil and Uruguay, calcareous downland, and the steppes of Europe. They are classified with temperate savannas and shrublands as the temperate grasslands, savannas, and shrublands biome. Temperate grasslands are the home to many large herbivores, such as bison, gazelles, zebras, rhinoceroses, and wild horses. Carnivores like lions, wolves and cheetahs and leopards are also found in temperate grasslands. Other animals of this region include: deer, prairie dogs, mice, jack rabbits, skunks, coyotes, snakes, fox, owls, badgers, blackbirds (both Old and New World varieties), grasshoppers, meadowlarks, sparrows, quails, hawks and hyenas.

Negri-Nepote Temperate Grasslands in New Jersey

Flooded

Grasslands that are flooded seasonally or year-round, like the Everglades of Florida, the Pantanal of Brazil, Bolivia and Paraguay or the Esteros del Ibera in Argentina.They are classified with flooded savannas as the flooded grasslands and savannas biome and occur mostly in the tropics and subtropics.

Watermeadows are grasslands that are deliberately flooded for short periods.

Montane

High-altitude grasslands located on high mountain ranges around the world, like the Páramo of the Andes Mountains. They are part of the montane grasslands and shrublands biome and also constitute tundra.

Tundra

Similar to montane grasslands, polar arctic tundra can have grasses, but high soil moisture means that few tundras are grass-dominated today. However, during the Pleistocene ice ages, a polar grassland known as steppe-tundra occupied large areas of the Northern hemisphere. These are in the tundra biome.

Desert and xeric

Also called desert grasslands, this is composed of sparse grassland ecoregions located in the deserts and xeric shrublands biome.

Fauna

Mites, insect larvae, nematodes and earthworms inhabit deep soil, which can reach 6 metres (20 ft) underground in undisturbed grasslands on the richest soils of the world. These invertebrates, along with symbiotic fungi, extend the root systems, break apart hard soil, enrich it with urea and other natural fertilizers, trap minerals and water and promote growth. Some types of fungi make the plants more resistant to insect and microbial attacks.

Grassland in all its form supports a vast variety of mammals, reptiles, birds, and insects. Typical large mammals include the Blue Wildebeest, American Bison, Giant Anteater and Przewalski's Horse.

While grasslands in general support diverse wildlife, given the lack of hiding places for predators, the African savanna regions support a much greater diversity in wildlife than do temperate grasslands.[5]

There is evidence for grassland being much the product of animal behaviour and movement;[6] some examples include migratory herds of antelope trampling vegetation and African Bush Elephants eating Acacia saplings before the plant has a chance to grow into a mature tree.

See also

References

  1. ^ a b University of California Museum of Paleontology Grasslands website. Ucmp.berkeley.edu. Retrieved on 2011-12-01.
  2. ^ NASA Earth Observatory webpage. Earthobservatory.nasa.gov. Retrieved on 2011-12-01.
  3. ^ Piperno, D. R.; Sues, HD (2005). "Dinosaurs Dined on Grass". Science 310 (5751): 1126–8. doi:10.1126/science.1121020. PMID 16293745. 
  4. ^ EO Experiments: Grassland Biome. Earthobservatory.nasa.gov. Retrieved on 2011-12-01.
  5. ^ University of California – Santa Barbara Temperate Grasslands website. Kids.nceas.ucsb.edu. Retrieved on 2011-12-01.
  6. ^ How can grazing heal land?. ManagingWholes.com. Retrieved on 2011-12-01.

Further reading

Temperate grasslands, savannas, and shrublands ecoregions

Al Hajar Al Gharbi montane woodlandsOman
Amsterdam and Saint-Paul Islands temperate grasslandsAmsterdam Island, Saint-Paul Island
Tristan da Cunha-Gough Islands shrub and grasslandsTristan da Cunha, Gough Island
Canterbury-Otago tussock grasslandsNew Zealand
Eastern Australia mulga shrublandsAustralia
Southeast Australia temperate savannaAustralia
California Central Valley grasslandsUnited States
Canadian aspen forests and parklandsCanada, United States
Central and Southern mixed grasslandsUnited States
Central forest-grasslands transitionUnited States
Central tall grasslandsUnited States
Columbia PlateauUnited States
Edwards Plateau savannaUnited States
Flint Hills tall grasslandsUnited States
Montana valley and foothill grasslandsUnited States
Nebraska Sand Hills mixed grasslandsUnited States
Northern mixed grasslandsCanada, United States
Northern short grasslandsCanada, United States
Northern tall grasslandsCanada, United States
Palouse grasslandsUnited States
Texas blackland prairiesUnited States
Western short grasslandsUnited States
Argentine EspinalArgentina
Argentine MonteArgentina
Humid PampasArgentina
Patagonian grasslandsArgentina, Chile
Patagonian steppeArgentina, Chile
Semi-arid PampasArgentina
Alai-Western Tian Shan steppeKazakhstan, Tajikistan, Uzbekistan
Altai steppe and semi-desertKazakhstan
Central Anatolian steppeTurkey
Daurian forest steppeChina, Mongolia, Russia
Eastern Anatolian montane steppeArmenia, Iran, Turkey
Emin Valley steppeChina, Kazakhstan
Faroe Islands boreal grasslandsFaroe Islands, Denmark
Gissaro-Alai open woodlandsKyrgyzstan, Tajikistan, Uzbekistan
Kazakh forest steppeKazakhstan, Russia
Kazakh steppeKazakhstan, Russia
Kazakh uplandKazakhstan
Middle East steppeIraq, Syria
Mongolian-Manchurian grasslandChina, Mongolia, Russia
Pontic steppeKazakhstan, Moldova, Romania, Russia, Ukraine
Sayan Intermontane steppeRussia
Selenge-Orkhon forest steppeMongolia, Russia
South Siberian forest steppeRussia
Tian Shan foothill arid steppeChina, Kazakhstan, Kyrgyzstan

Tropical and subtropical grasslands, savannas, and shrublands ecoregions

Angolan Miombo woodlandsAngola
Angolan Mopane woodlandsAngola, Namibia
Ascension scrub and grasslandsAscension Island
Central Zambezian Miombo woodlandsAngola, Burundi, Democratic Republic of the Congo, Malawi, Tanzania, Zambia
East Sudanian savannaCameroon, Central African Republic, Chad, Democratic Republic of the Congo, Eritrea, Ethiopia South Sudan, Sudan, Uganda
Eastern Miombo woodlandsMozambique, Tanzania
Guinean forest-savanna mosaicBenin, Burkina Faso, Cameroon, Gambia, Ghana, Guinea, Guinea Bissau, Ivory Coast, Nigeria, Senegal, Togo
Itigi-Sumbu thicketTanzania, Zambia
Kalahari Acacia-Baikiaea woodlandsBotswana, Namibia, South Africa, Zimbabwe
Mandara Plateau mosaicCameroon, Nigeria
Northern Acacia-Commiphora bushlands and thicketsEthiopia, Kenya, South Sudan, Uganda
Northern Congolian forest-savanna mosaicCameroon, Central African Republic, Democratic Republic of the Congo, South Sudan, Uganda
Sahelian Acacia savannaBurkina Faso, Cameroon, Chad, Eritrea, Ethiopia, Mali, Mauritania, Niger, Nigeria, Senegal, South Sudan, Sudan
SerengetiKenya, Tanzania
Somali Acacia-Commiphora bushlands and thicketsEritrea, Ethiopia, Kenya, Somalia
Southern Acacia-Commiphora bushlands and thicketsKenya, Tanzania
Southern Africa bushveldBotswana, South Africa, Zimbabwe
Southern Congolian forest-savanna mosaicAngola, Democratic Republic of the Congo
Southern Miombo woodlandsMalawi, Mozambique, Zambia, Zimbabwe
Saint Helena scrub and woodlandsSaint Helena
Victoria Basin forest-savanna mosaicBurundi, Ethiopia, Kenya, Rwanda, South Sudan, Tanzania, Uganda
West Sudanian savannaBenin, Burkina Faso, Gambia, Ghana, Guinea, Ivory Coast, Niger, Nigeria, Senegal
Western Congolian forest-savanna mosaicAngola, Democratic Republic of the Congo, Republic of the Congo
Western Zambezian grasslandsAngola, Zambia
Zambezian and Mopane woodlandsBotswana, Malawi, Mozambique, Namibia, South Africa, Swaziland, Zambia, Zimbabwe
Zambezian Baikiaea woodlandsAngola, Botswana, Namibia, Zambia, Zimbabwe
Arnhem Land tropical savannaAustralia
Brigalow tropical savannaAustralia
Cape York tropical savannaAustralia
Carpentaria tropical savannaAustralia
Einasleigh upland savannaAustralia
Kimberly tropical savannaAustralia
Mitchell grass downsAustralia
Trans Fly savanna and grasslandsIndonesia, Papua New Guinea
Victoria Plains tropical savannaAustralia
Terai-Duar savanna and grasslandsBhutan, India, Nepal
Western Gulf coastal grasslandsMexico, United States
Aripo SavannasTrinidad
Beni savannaBolivia
Campos Rupestres montane savannaBrazil
CerradoBolivia, Brazil, Paraguay
Clipperton Island shrub and grasslandsClipperton Island is an overseas territory of France
Córdoba montane savannaArgentina
Guyanan savannaBrazil, Guyana, Venezuela
Gran ChacoArgentina, Brazil, Paraguay
Los LlanosVenezuela, Colombia
Uruguayan savannaArgentina, Brazil, Uruguay
Hawaiian tropical high shrublandsHawaiʻi
Hawaiian tropical low shrublandsHawaiʻi
Northwestern Hawaii scrubHawaiʻi