Saturday, May 14, 2011

Grassland biome


TROPICAL GRASSLANDS

           Tropical grasslands, or savannas, are also the homes of primates in Africa and Asia; no savanna-living primates exist in South America. Tropical grasslands comprise a mixture of trees and grasses, the proportion of trees to grass varying directly with the rainfall. Areas of high seasonal rainfall support single-story woodlands of tall trees, while lush grasses form the ground vegetation.
           Tropical grasslands, or savannas, lie north and south of tropical rain forests that are on the equator. Some areas beyond savannas are hot deserts. Other savannas may be lined with mountains, dense forests, and seas. South America is home to several large savannas. An example of one of these savannas is the llanos, which means plains, located in the Orinoco River basin. The llanos is north of the Amazon forests and is shared in areas of Columbia and Venezuela. It is the size of France or Texas. Another large tropical grassland can be found south of the Amazon forest in the Brazilian Highlands, called campos. Other South American grasslands can be found in southeast Venezuela and southern Guyana.

          The worlds largest savannas can be found in Africa. The savanna takes up almost half of the continent. It stretches from the Atlantic coast of West Africa to the east across Sudan, and then goes south through east Africa. From Mozambique the savanna heads west and goes through Zambia and Angola, back to the Atlantic Ocean (Lambert, 30). Other savannas can be found in India's great Deccan Plateau, and in Australia, north of central deserts.

TEMPERATE GRASSLANDS

         The temperate grasslands are located in the mid-latitudes on planet Earth. These include the Prairies of North America, Pampas of South America and the Steppes of Eurasia. The temperate grasslands are further divided on the basis of their general characteristics. The best example of this is the Prairie biome of North America. In semi-arid regions - which are typically characterized by growth of short grass, the Prairies are known as Short-grass Prairies, while the same in regions with high rainfall - typically characterized by growth of tall grass, they are known as Tall-grass Prairies. This is just one of the numerous lesser known attributes of this grassland biome.
         Temperate grasslands are a division of a larger biome grouping of grasslands that includes tropical savannas.  Both biome types are characterized by a dominance of grasses, yet temperate grasslands differ significantly from savannas.  First unlike savannas that can have trees and shrubs scattered throughout, temperate grasslands have trees and shrubs absent.  Temperate grasslands are also found in less tropical ecosystems and thus have a larger temperate fluctuation during the year.  Temperatures in temperate grasslands can vary tremendously which has a large impact on growing seasons.  Generally they also have less rainfall. 

Regional Expressions: Temperate Grasslands are found throughout the globe, generally in the interiors of the continents and north or south of the tropic of cancer/Capricorn.  The following are the major regional expressions of grasslands recognized around the globe.
  • Veldts of South Africa
  • Puszta of Hungary
  • Pampas of Argentina/Uruguay
  • Steppes of Russia / China
  • Plains and Prairies of North America
Minor Expressions: There are smaller local expressions of grasslands as well.  These include the following:
  • Australian Outback
  • Minnesota Cedar Creek Region
       Biodiversity: Grasslands (temperate) are dominated by one or a few species of grasses while there are several hundred other types of grasses and non-woody flowering plants that while less abundant make up a vital part of the species composition. There are many types of grass species that are dominant species in their own region.  Each species of grass grows better with varying temperatures / rainfall / and soil conditions.  Grasses are dominant (instead of trees) because of fire, drought and grazing by large herbivores. 
       Drought: Drought plays a large role in keeping trees from taking over the grasslands.  Some years receive less rain than others, just as certain seasons receive significantly less rain than others.  Trees generally can not stand the lack of water as easily as grasses and thus grasses remain dominant.

       Fire: Fire plays a big role in this biome, preserving biodiversity and keeping trees from overtaking the grasses.  Lightning from large storms rolling over the grasslands ignites large grass-fires.  These fires help certain plants by germinating seeds, clearing ground cover to allow rare plants a chance and by nourishing the soil with freshly burnt vegetation.

         Soil: The soil of the temperate grasslands is deep and dark.  The upper layers are the most fertile because of the buildup of many layers of dead branching stems and roots.  This organic mater on the surface and in the dead roots provide a great degree of nourishment for the living plants.

         Rainfall: Rainfall is generally less in temperate grasslands than in tropical savannas, although drought usually plays less of a roll effecting biodiversity than it does in savannas.  Rain usually falls in temperate grasslands in the late spring and early summer.  There is an average of 20 – 35 inches of rainfall a year.  The amount of rainfall however determines the height of grasses in the grassland.  For north America, this rainfall gradient helps to divide the temperate grasslands into tall grass prairies (in wetter areas) and short grass steppes (in dryer habitats).

         Environmental concerns: There is a great concern for remaining grasslands in temperate regions.  Because the soil in these areas is incredibly rich and the land is flat and treeless, most of this biome has been turned into farms or ranches.  The result of this overuse and consumption of the grassland by agricultural practices is a fragmentation of once large tracks of grassland.  Fragmentation decreases biodiversity (Theory of Island Biogeography).  Plowing of grasslands, combined with wind has lead to huge dust storms, such as those which created the Great Dust Bowl in the American Depression of the mid 1920s.  Finally, in dryer areas, overgrazing and salt build-up from irrigation of the land have turned these areas into near-wastelands.
          Floral Diversity: The most common grasses include blue gamma grass, buffalo grass, Johnson grass, and various sorts of wheat and burley.  Common flowers include types of asters, coneflowers, Solidagos (goldenrods), vetches, Indian blankets and sweet clovers.

          Fauna Diversity: In North America common animals include: bison, pronghorns, deer, mice, rabbits, grouse, badgers, skunks, meadowlarks, various  owls, garter snakes, rattle-snakes, red-tailed hawks and prairie dogs.