The Earth’s biomes include the forests, marine and ocean, tundra, grassland and desert biomes. The grassland biomes are the magical places of the earth that are dominated by grasses, far fewer trees, and woody plants that go on seemingly forever and beyond the horizon.
When forests decline and continental climates that are favorable develop, grasslands develop. As weather becomes hotter and drier, grasslands are more likely to sustain themselves as viable biomes, or habitats for living things that have adapted to the new conditions.
The first grasslands are believed to have developed after the Pleistocene Ice Ages, especially as mountains rose in North America and the warmer, drier climates developed.
As with the forest biomes, there are tropical grasslands and temperate grasslands. Each country has its own name for various grasslands of the Earth, so there are many names, including pampas, savannah, chaparral (what is chaparral biome), prairie, puszta, veldt, and steppe as the most recognizable.
The temperate grasslands include grasses as the dominant plant or vegetation. In the Colorado Prairie, trees and larger bushes or shrubs are almost absent. The climate has more variation from hot in summer and cold in winter than in the tropical grassland or savannah. There is more annual rainfall in the temperate grassland, which can determine whether grasses grow taller or are shorter in height.
Generally, prairies have longer grasses while steppes have shorter grasses. The prairies have more rainfall, perhaps more rich soil from decaying plant material, and thus encourage growth.
Temperate and tropical grasslands are affected by drought, various fires that flare up occasionally, and by animals which are very damaging to the larger trees and hardier shrubs. This makes it hard for many trees and woody shrubs from becoming established. But hardy trees that grow in river valleys of the grassland will include oaks, cottonwoods and willows.
Temperate grassland soil is far richer, deeper and darker than tropical savannah or grassland soil, due to the larger amount of dead and decaying plant material that provides richness. As a result, temperate grassland plants can establish deeper and stronger root systems that help them to survive.
Non woody plants and hundreds of species of flowering plants grow in temperate grasslands. The grasses include needle grasses and grasses with long, slender leaves. There are also star grasses and seedy grasses such as wild rice. Temporate grasslands also host ryegrass, wild oats, blue grama, buffalo grass, and galletas. Flowering plants are actually “forbs”, a class of plant that we call “wildflowers”. These include asters, lupine, milkweed, coneflowers, stars, goldenrods, sunflowers, clovers, psoraleas and wild indigo.
The grasses are monocots, with one cotyledon. These grasses have a distinct growth form, usually spread pollen by wind, and do not have showy flowers. Less prominent are diots with showy flowers that attract insects and other species of pollinators. Other plants are deceptive and have the appearance of grasses when they are not grasses.
Tropical grasslands, or savannahs, are generally in latitudes that lie between the Tropic of Cancer and the Tropic of Capricorn. The Savannah undergoes seasonal drought, occasional fires that can spread quickly and across massive areas.
The soil of the savannah is porous with rapid drainage and thin layers of humus. Drier savannas, such as the Serengeti plains will have Rhodes grass and red oat grass. Star grasses, lemon grasses and deciduous trees and shrubs can be found in other African continent savannahs.
In the Kenyan, Tanzanian and Ugandan grasslands/savannahs, trees grow in groups and only over termite mounds, because any other soil is to thin to support them. These are called “group tree” grasslands.
In summary, grasslands are predominantly populated by grasses, have non existent or widespread trees, short woody shrubs, and wildflowers. The height of the grass, presence of other plants, and quality of the soil depends on the annual rainfall, the variations in temperature, and the amount of dead and decaying plant material. The two categories of grassland are temperate and tropical.
Many grasslands have been converted, through the diversion of water and through tending, into grazing lands and farm lands. The biggest threat to grasslands is overgrazing or poor crop management which can lead to destruction of the soil structure and ultimate desertification.
CITATIONS:
http://www.marietta.edu/_biol/biomes/grass.htm
http://en.wikipedia.org/wiki/Grassland_biomes
http://www.ucmp.berkeley.edu/exhibits/biomes/grasslands.pho
