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1. 緑の芝生(芝地)

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2018/03/31 05:52:16」(JST)

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This article is about vegetation and landscape. For other uses, see Grassland (disambiguation).

"Greensward" redirects here. For park plan, see Central Park.

Grassland in Magallanes Region, Patagonia, Chile

A grassland in the Philippines

An Inner Mongolian grassland in the People's Republic of China

Grasslands are areas where the vegetation is dominated by grasses (Poaceae); however, sedge (Cyperaceae) and rush (Juncaceae) families can also be found along with variable proportions of legumes, like clover, and other herbs. 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 grassland, to quite tall, as in the case of North American tallgrass prairie, South American grasslands and African savanna.

The Konza tallgrass prairie in the Flint Hills of northeastern Kansas

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.

As flowering plants and trees, grasses grow in great concentrations in climates where annual rainfall ranges between 500 and 900 mm (20 and 35 in). 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 feces (coprolites) have been found containing phytoliths of a variety of grasses that include grasses that are related to modern rice and bamboo.

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.

Climates

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. 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, where woody encroachment is prevented as low nutrient levels in the soil may inhibit the growth of forest and shrub species.

Biodiversity and conservation

Grasslands dominated by unsown wild-plant communities ("unimproved grasslands") can be called either natural or "semi-natural" habitat. 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, including grasses, sedges, rushes, and herbs; 25 or more species per square meter is not unusual. Chalk downlands in England can support over 40 species per square meter. In many parts of the world, few examples have escaped agricultural improvement (fertilizing, weed killing, plowing or re-seeding). For example, original North American 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; there are also 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 most threatened types of habitat, 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

Grassland vegetation often remains dominant in a particular area usually due to grazing, cutting, or natural or man-made fires, all discouraging colonization by and survival of tree and shrub seedlings. Some of the world's largest expanses of grassland are found in the 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 U.S. 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.

The professional study of grasslands falls under the category of rangeland management, which focuses on ecosystem services associated with the grass-dominated arid and semi-arid rangelands of the world. Rangelands account for an estimated 70% of the earth's landmass; thus, many cultures including those of the United States are indebted to the economics that the world's grasslands have to offer, from producing grazing animals, tourism, ecosystems services such as clean water and air, and energy extraction.

Types of grasslands

Schimper (1898)

Grassland types by Schimper (1898, 1903):

• meadow (hygrophilous or tropophilous grassland)
• steppe (xerophilous grassland)
• savannah (xerophilous grassland containing isolated trees)

Ellenberg and Mueller-Dombois (1967)

Grassland types by Ellenberg and Mueller-Dombois (1967):

• Formation-class V. Terrestrial herbaceous communities
  • A. Savannas and related grasslands (tropical or subtropical grasslands and parklands)
  • B. Steppes and related grasslands (e.g. North American "prairies" etc.)
  • C. Meadows, pastures or related grasslands
  • D. Sedge swamps and flushes
  • E. Herbaceous and half-woody salt swamps
  • F. Forb vegetation

Laycock (1979)

Grassland types by Laycock (1979):

• (1) tallgrass (true) prairie;
• (2) shortgrass prairie;
• (3) mixed-grass prairie;
• (4) shrub steppe;
• (5) annual grassland;
• (6) desert (arid) grassland;
• (7) high mountain grassland.

Other

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 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, 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

Grassland in the Antelope Valley, California

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 prairies

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.

Animals

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.

There is evidence for grassland being much the product of animal behaviour and movement; 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

• Appalachian bald
• Biomes
• Bunch grass
• Bushveld
• Cerrado
• Coastal plain
• Dambo
• Desert
• Field
• Flood-meadow
• Flooded grasslands and savannas
• Llanos
• Lowland semi-natural grassland
• Meadow
• Pacific grasslands
• Pampa
• Pasture
• Plain
• Plateau
• Prairie
• Savanna
• Sods
• Steppe
• Taiga
• Tundra
• Veld
• Water-meadow
• Wet meadow

Temperate grasslands, savannas, and shrublands ecoregions

• The grassland Ecoregions of the Temperate grasslands, savannas, and shrublands Biome are:

Afrotropic Temperate grasslands, savannas, and shrublands
Al Hajar Al Gharbi montane woodlands	Oman
Amsterdam and Saint-Paul Islands temperate grasslands	Amsterdam Island, Saint-Paul Island
Tristan da Cunha-Gough Islands shrub and grasslands	Tristan da Cunha, Gough Island

Australasia Temperate grasslands, savannas, and shrublands
Canterbury-Otago tussock grasslands	New Zealand
Eastern Australia mulga shrublands	Australia
Southeast Australia temperate savanna	Australia

Nearctic Temperate grasslands, savannas, and shrublands
California Central Valley grasslands	United States
Canadian aspen forests and parklands	Canada, United States
Central and Southern mixed grasslands	United States
Central forest-grasslands transition	United States
Central tall grasslands	United States
Columbia Plateau	United States
Edwards Plateau savanna	United States
Flint Hills tall grasslands	United States
Montana valley and foothill grasslands	United States
Nebraska Sand Hills mixed grasslands	United States
Northern mixed grasslands	Canada, United States
Northern short grasslands	Canada, United States
Northern tall grasslands	Canada, United States
Palouse grasslands	United States
Texas blackland prairies	United States
Western short grasslands	United States

Neotropic Temperate grasslands, savannas, and shrublands
Argentine Espinal	Argentina
Argentine Monte	Argentina
Humid Pampas	Argentina
Patagonian grasslands	Argentina, Chile
Patagonian steppe	Argentina, Chile
Semi-arid Pampas	Argentina

Palearctic temperate grasslands, savannas, and shrublands
Alai-Western Tian Shan steppe	Kazakhstan, Tajikistan, Uzbekistan
Altai steppe and semi-desert	Kazakhstan
Central Anatolian steppe	Turkey
Daurian forest steppe	China, Mongolia, Russia
Eastern Anatolian montane steppe	Armenia, Iran, Turkey
Emin Valley steppe	China, Kazakhstan
Faroe Islands boreal grasslands	Faroe Islands, Denmark
Gissaro-Alai open woodlands	Kyrgyzstan, Tajikistan, Uzbekistan
Kazakh forest steppe	Kazakhstan, Russia
Kazakh steppe	Kazakhstan, Russia
Kazakh Uplands	Kazakhstan
Middle East steppe	Iraq, Syria
Mongolian-Manchurian grassland	China, Mongolia, Russia
Pontic steppe	Kazakhstan, Moldova, Romania, Russia, Ukraine, Bulgaria
Sayan Intermontane steppe	Russia
Selenge-Orkhon forest steppe	Mongolia, Russia
South Siberian forest steppe	Russia
Tian Shan foothill arid steppe	China, Kazakhstan, Kyrgyzstan

Tropical and subtropical grasslands, savannas, and shrublands ecoregions

Afrotropic Tropical and subtropical grasslands, savannas, and shrublands
Angolan Miombo woodlands	Angola
Angolan Mopane woodlands	Angola, Namibia
Ascension scrub and grasslands	Ascension Island
Central Zambezian Miombo woodlands	Angola, Burundi, Democratic Republic of the Congo, Malawi, Tanzania, Zambia
East Sudanian savanna	Cameroon, Central African Republic, Chad, Democratic Republic of the Congo, Eritrea, Ethiopia South Sudan, Sudan, Uganda
Eastern Miombo woodlands	Mozambique, Tanzania
Guinean forest-savanna mosaic	Benin, Burkina Faso, Cameroon, Gambia, Ghana, Guinea, Guinea Bissau, Ivory Coast, Nigeria, Senegal, Togo
Itigi-Sumbu thicket	Tanzania, Zambia
Kalahari Acacia-Baikiaea woodlands	Botswana, Namibia, South Africa, Zimbabwe
Mandara Plateau mosaic	Cameroon, Nigeria
Northern Acacia-Commiphora bushlands and thickets	Ethiopia, Kenya, South Sudan, Uganda
Northern Congolian forest-savanna mosaic	Cameroon, Central African Republic, Democratic Republic of the Congo, South Sudan, Uganda
Sahelian Acacia savanna	Burkina Faso, Cameroon, Chad, Eritrea, Ethiopia, Mali, Mauritania, Niger, Nigeria, Senegal, South Sudan, Sudan
Serengeti	Kenya, Tanzania
Somali Acacia-Commiphora bushlands and thickets	Eritrea, Ethiopia, Kenya, Somalia
Southern Acacia-Commiphora bushlands and thickets	Kenya, Tanzania
Southern Africa bushveld	Botswana, South Africa, Zimbabwe
Southern Congolian forest-savanna mosaic	Angola, Democratic Republic of the Congo
Southern Miombo woodlands	Malawi, Mozambique, Zambia, Zimbabwe
Saint Helena scrub and woodlands	Saint Helena
Victoria Basin forest-savanna mosaic	Burundi, Ethiopia, Kenya, Rwanda, South Sudan, Tanzania, Uganda
West Sudanian savanna	Benin, Burkina Faso, Gambia, Ghana, Guinea, Ivory Coast, Niger, Nigeria, Senegal
Western Congolian forest-savanna mosaic	Angola, Democratic Republic of the Congo, Republic of the Congo
Western Zambezian grasslands	Angola, Zambia
Zambezian and Mopane woodlands	Botswana, Malawi, Mozambique, Namibia, South Africa, Swaziland, Zambia, Zimbabwe
Zambezian Baikiaea woodlands	Angola, Botswana, Namibia, Zambia, Zimbabwe

Australasia Tropical and subtropical grasslands, savannas, and shrublands
Arnhem Land tropical savanna	Australia
Brigalow tropical savanna	Australia
Cape York tropical savanna	Australia
Carpentaria tropical savanna	Australia
Einasleigh upland savanna	Australia
Kimberley tropical savanna	Australia
Mitchell grass downs	Australia
Trans Fly savanna and grasslands	Indonesia, Papua New Guinea
Victoria Plains tropical savanna	Australia

Indomalaya Tropical and subtropical grasslands, savannas, and shrublands
Terai-Duar savanna and grasslands	Bhutan, India, Nepal

Nearctic Tropical and subtropical grasslands, savannas, and shrublands
Western Gulf coastal grasslands	Mexico, United States

Neotropic Tropical and subtropical grasslands, savannas, and shrublands
Aripo Savannas	Trinidad
Beni savanna	Bolivia
Campos rupestres	Brazil
Cerrado	Bolivia, Brazil, Paraguay
Clipperton Island shrub and grasslands	Clipperton Island is an overseas territory of France
Córdoba montane savanna	Argentina
Guianan savanna	Brazil, Guyana, Venezuela
Gran Chaco	Argentina, Brazil, Paraguay
Los Llanos	Venezuela, Colombia
Uruguayan savanna	Argentina, Brazil, Uruguay

Oceania Tropical and subtropical grasslands, savannas, and shrublands
Hawaiian tropical high shrublands	Hawaiʻi
Hawaiian tropical low shrublands	Hawaiʻi
Northwestern Hawaii scrub	Hawaiʻi

Further reading

• Courtwright, Julie. 2011. Prairie Fire: A Great Plains History. University Press of Kansas. 274 pp.
• French, N. R. (ed.). 1979. Perspectives in Grassland Ecology. Springer, New York, 204 pp., [4].
• Suttie, J. M.; Reynolds, S. G.; C. Batello. 2005. Grasslands of the world. Rome: FAO. [5].

Japanese Journal

• 近代都市公園の発生と展開に関する研究 : ニューヨーク・セントラル・パークのデザインについて

• 造園雑誌 40(1), 47-56, 1976-07-25
• NAID 110004659354

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