grassland

The Konza tallgrass prairie in the Flint Hills of northeastern Kansas.

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

A restored grassland ecosystem at Morton Arboretum in Illinois.

Grasslands are areas where the vegetation is dominated by grasses (Poaceae) and other herbaceous (non-woody) plants (forbs). Grasslands occur naturally on all continents except Antarctica, and in many other areas they have replaced the natural vegetation due to human influence. Grassland vegetation varies from that dominated solely by herbaceous species to that in which woody plants also occur and trees may be co-dominant with the grasses. In temperate latitudes, such as north-west Europe, grasslands are dominated by perennial species, whereas in warmer climates annual species form a greater component of the vegetation^{[citation needed]}. Grasslands are very varied and can be found in most terrestrial climates. Grassland vegetation can vary in height from very short, as in chalk downland where the vegetation may be less than 30 cm high, to quite tall, as in the case of North American tallgrass prairie, South American grasslands and African savannah. Grassland, shrubland and desert environments cover two-thirds of the world's land surface ^{[citation needed]}. In countries where modern agriculture has not destroyed wild grasslands, the greatest diversity of grazing animals and predators on the planet calls these open habitats their home^{[citation needed]}. Grassland habitats appeared on Earth some 70 or 80 million years ago^{[citation needed]}.

As flowering plants, grasses grow in great concentrations in climates where annual rainfall ranges between 10 and 39 inches ^{[citation needed]}. The root systems of perennial grasses and forbs form complex mats that hold the soil in place. Mites, insect larvae, nematodes and earthworms inhabit deep soil, which can reach 20 feet 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 (Chadwick 1995). Some types of fungi make the plants more resistant to insect and microbial attacks.

Climate and grasslands

Grasslands receive about 380 to 900 mm (15 to 36 in) of rain per year^{[citation needed]} compared to deserts, which receive less than 300 mm (12 in) and tropical rainforests, which receive more than 2,000 mm (80 in)^{[citation needed]}. While extreme temperatures may occur in some grasslands, normally they range between -20 to 30 degrees Celsius^{[citation needed]}. Tropical grasslands have dry and wet seasons, but remain warm all the time^{[citation needed]}. Temperate grasslands have cold winters and warm summers with rain or some snow. Since some grasses die back above ground annually^{[citation needed]}, the soil and the sod protect the roots and the new buds from the cold of winter or dry conditions.

Grassland biodiversity and conservation

The true grasslands are those where wild-plant communities naturally occur^{[citation needed]}. This is where grasslands have remained undisturbed by agricultural improvement. In many parts of the world, examples that have escaped agricultural improvement (fertilising, weed killing, ploughing or re-seeding) contain many species of wild plants - grasses, sedges, rushes and herbaceous species - 25 or more species per square metre is not unusual^{[citation needed]}. However, such examples, such as original North American prairie or lowland 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" - for example snipe, or the Great Bustard. Agricultural grasslands are usually poor in wild plant species due to the original diversity of plants having been destroyed by cultivation^{[citation needed]}, 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^{[citation needed]}. In many parts of the world "unimproved" grasslands are one of the most 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

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 (such as for hay), or natural or man-made fires, all discouraging colonisation by and survival of tree and shrub seedlings^{[citation needed]}. Fire was used in North America by the Native Americans as a means of maintaining grassland^{[citation needed]}. Some of the world's largest expanses of grassland are found in African savannah, and these are maintained by wild herbivores as well as by nomadic pastoralists and their cattle, sheep or goats^{[citation needed]}.

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 American Midwest may have been extended eastward into Illinois, Indiana, and Ohio by human agency. Much grassland in north-west Europe developed after the Neolithic Period, when people gradually cleared the forest to create areas for raising their livestock.

Types of grassland

Tropical and subtropical grasslands

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 grasslands

Mid-latitude grasslands, including the Prairie of North America, the Pampa of Argentina, 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 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, grasshoppers, meadowlarks, sparrows, quails, and hawks.

Flooded grasslands

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

Montane grasslands

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 alpine tundra.

Polar grasslands

Similar to montane grasslands, arctic tundra can have grasses. However 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.

Xeric grasslands

Also called desert grasslands, these are sparse grasslands located in deserts and xeric shrublands ecoregions.Grasslands have great biological diversity and stability; they are able to resist plant disease and drought. As such, they represent invaluable genetic banks. This diversity is being studied by scientists around the world and consequently uncovering chemical and biological secrets. Agriculture and other food production will profit from this emerging knowledge.

See also

• Coastal plain
• Dambo
• Desert
• Field
• Flooded grasslands and savannas
• Flood-meadow
• Llanos
• Meadow
• Pampa
• Pasture
• Plain
• Plateau
• Prairie
• Savanna
• Steppe
• Taiga
• Tundra
• Veld
• Water-meadow
• Wet meadow

References

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