Most of the ecologists have tried to categorize the principal terrestrial vegetation types into which the world is divided. This world vegetation types have come to be identified as biomes. Aquatic biomes are as well acknowledged. The biomes are numerous and the different types will be studied here.
Definition of Biomes:
Biomes are geographically and climatically defined regions or areas of ecologically similar feature appearance of communities of animals, plants and soil organisms. Biomes are stated by the factors like plant structures (that is, shrubs, trees and grasses), leaf types (like broadleaf and needle leaf) plant spacing (like forest, woodland, savanna) and climate. Climate is a main factor finding out the distribution of terrestrial biomes. The significant climatic factors comprise:
a) Latitude: Arctic, boreal, temperate, subtropical and tropical.
b) Humidity: humid, semi-humid, arid and semi-arid.
c) Seasonal Variation: Rainfall might be distributed all through the year or be marked by the seasonal variation.
d) Dry summer, wet winter: Most of the areas of the earth obtain most of their rainfall all through the summer months. Mediterranean climate areas receive their rainfall all through winter months.
e) Elevation: Rising elevation causes a distribution of habitat types identical to that of increasing latitude.
Classification of Biomes:
Generally, biome classification schemes seek to state or define biomes by using climatic measurements in specific latitude (or temperature zoning) and humidity.
Though, no two ecologists or taxonomists seem to agree on a system of categorization so, it is hardly surprising that a definitive list of biomes can't be produced.
The major categorization of biomes will be looked into:
Tropical Rain Forest:
Tropical rainforests take place near the equator where the rainfall is plentiful and takes place all through the year. They are found in South and Central America specifically in and around the Amazon basin, West and Equatorial Africa, South-East Asia, Indonesia and North-east Australia. This frequent combination of warmth and moisture lets continuous plant growth to take place. The tropical rainforest is the richest biome in terms of number of species probably having at least half of the species of terrestrial organisms.
Contrast to popular belief, undisturbed tropical rainforest is not impenetrable. This is because so little light is capable to get through to the forest floor which relatively few plants can grow there. Most of the trees in the canopy are covered through epiphytes (that is, plants growing on other plants) and some other trees generate aerial roots that absorb nutrients just as roots in the soil do. Much of the animal life is confined for most of the time to the canopy. Fruits are found all through the year and specialized fruit eaters have developed among the insects, the birds and the primates. A few other animals concentrate on feeding on leaves for illustration, the species of sloth in tropical South American forests.
Tropical Seasonal Forest:
Close to tropical rain forests are tropical seasonal forests which take place in humid tropical climates having a clear dry season throughout the period trees lose their leaves. They are found in South-east Asia, India, West and East Africa, South and Central America and Northern Australia. The seasonality makes their habitat less diverse than the rain forests. Tropical seasonal forests are frequently found as well where monsoons take place example: India. The monsoons give seasonal rains as well.
Savannahs are tropical grasslands often have scattered trees. They are most extensive in Africa however is as well found in South America, Australia and Southern Asia. Savannah is subjected to fire either from the lightning or started by humans. Much of the African Savannah is burnt each and every year which has made savannah trees have thick bark which insulates the living cambium from the heat of the fire. The grassland or savannah of Africa is famed for its plenty of wildlife being inhabited by herds of grazing animal and their related predators. The plentiful herbivores comprising Buffalo, Zebra, gazelle and Giraffe support high numbers of mammalian carnivores such as Leopard, lion, Cheetah and Spotted Hyena among others.
On a worldwide scale, the savannah biome is transitional among tropical rainforest and desert. In general, it records rainfall between 90 to 150 cm annually. Temperatures yearly fluctuate more in this biome than in the tropical rain forest and there is seasonal drought.
Savannahs have frequently been transformed to agricultural purposes all through the world and give most of the agricultural products for most of the tropical and subtropical countries.
Deserts are found all through the world, mostly in the subtropical zone among 15 and 400 north and south of the equator. Deserts generally receive less than 50mm of rain a year and the rain is random. As the vegetation is sparse and the skies are generally clear, deserts give out heat fast at night. This leads to great daily changes in temperature, at times exceeding 30oc between day and night.
In summer day, temperatures in deserts are very hot frequently exceeding 40oc however nights are cool or cold. For most desert organisms the key to survival is being capable to make use of the occasional heavy rain falls.
A few ephemeral plants utilize the occasion to germinate, grow flower and produce seeds in the space of 20 to 30 days. Others survive as perennials as underground bulbs or corns having the above ground parts shooting out after heavy rain. Others such as cacti are succulent having thick cuticles and sunken stomata which just open at night to reduce the transpiration losses. Trees and shrubs which live in deserts often encompass deep roots which reach sources of water far beneath the surface of the ground.
Animals in the desert experience a fearsome array of problems. A broad variety of methods have evolved to deal with the problems. To avoid high temperatures, most of the desert vertebrates live in deep, cool and at times even rather moist burrows. Active ones just emerge at night when the temperatures are comparatively cool. Camels can drink huge amount of water when it is available and can then safely endure the loss of much of it as they can tolerate a 30% loss of their total water content. Most of the mammals die if 14% of their water is lost.
Temperate rainforests take place all along the pacific coast of New Zealand, North America, Australia and Chile. Their climate is cool and maritime, deficient in great variation in temperature and with plentiful summer rain and much cloudiness and fog. Similar to with the tropical rainforest, they have rain all through the year. However at times of the year, the so called rain is condensed fog. The trees in the temperate rain-forests are the tallest in the world. In Australia, the dominant tree of such forests is the mountain ash (that is, Eucalyptus regnans) that can grow to over 90 m in height. In North America, the dominant tree is redwood (that is, Sequoia sempervirens) which might be as high as 100 m.
Temperate Deciduous Forest:
Temperate deciduous forests grow in the continental climates of Northern hemisphere in regions having relatively warm summers and cold or severe winters. The biome covers big areas comprising much of Asia, eastern United States and Canada. Yearly precipitation is usually from 750 to around 2500 mm and is well distributed all through the year however water is in general unavailable during the winter since it is frozen. Trees are the dominant life form and the most plentiful species are the oaks.
Where there is less precipitation, the temperate deciduous forests are substituted by temperate grassland.
Temperate grasslands are found across large regions of Eastern Europe and Asia where they are termed as steppe; Central North America where they are termed prairie and Argentina where they are known as pampas.
The summers are hot and the winters cold having the continental climate moderately dry having among 200 to 750 mm of rain yearly. The flora of such temperate grasslands is governed by the perennial grasses.
The Eurasian steppes lie among the forests to the north and the deserts to the south. Most of the steppe has now been dedicated to the production of wheat. Much wheat is as well produced in the prairies of North America as temperate grasslands are appropriate to agriculture when they receive adequate precipitation.
Boreal Forest (Taiga):
Boreal forest is as well termed as taiga. It expands from north-eastern Europe across Russia to the Pacific Ocean and right across North America from Alaska to the newfound land. To the North it combines into tundra; and to the south, it grades to temperate deciduous forest or grassland. It can be much cold in the taiga. In winter, taiga obtains a deep blanket of snow and for much of the year, snow lies on the ground. Eastern Siberia is the coldest region in the northern hemisphere with a January temperature of -50 to -60oc. Because of the latitude where boreal forest occurs the days are short in winter (as small as 6 hours) and correspondingly long in the summer.
The vegetation of boreal forest is governed by coniferous trees mainly, hemlock, spruce and fir. Most of the trees tend to take place in dense stands of one or a few species. Throughout summer, plants might grow quickly and crops frequently attain a big size in a surprisingly short time.
With the harsh winters, the taiga causes severe problems for the animals found in it. Some of the mammals and birds migrate; some remain active throughout the long dark winter, like the community of rodents and other animals underneath the thick cover of snow where they are fully protected from most predators and some of the mammals hibernate. Large animals which live here comprise herbivores such as moose, deer and carnivores like wolves, bear and lynx. This area is traditionally acknowledged for fur trapping and lumber producing.
Farthest north in Eurasia, North America and their related Islands among the taiga and the permanent ice, occurs the open often boggy low treeless vegetation termed as tundra. It is a huge biome, very uniform in appearance which covers a fifth of the earth's land surface. The growing season is too short, the winters too cold and dry and the soil too unstable to support the trees. The trees present are small and are generally confined to the margins of streams and lakes. Usually, tundra is dominated through scattered patches of grasses and sedges (grass like plants) heathers, lichens and dwarf willows. The growing season is so small that some plants are annuals.
If the short growing season does arrive, plant growth and flowering might be spectacular with enormous regions bathed in color. The fast growth of plants is with food stored underground by the plants. Great numbers of insects rapidly appear and for some weeks productivity is high before winter sets in again for most of the year. Large grazing animals comprising musk-oxen, reindeer, caribou and carnivores like foxes, wolves and lynx live in the tundra which teems by life in the short summer.
Temperate Shrub land (Mediterranean):
This biome is well-known for winter rainy season and summer drought. It has what is frequently termed as Mediterranean climate and is found around the Mediterranean area itself; California, central Chile, the Cape area of South Africa and Southwestern Australia. The yearly rainfall is around 300 - 800 mm and throughout the summer there is generally no rain for around four months. The vegetation is much similar in these separated areas even though the individual plant species vary greatly among the regions. This biome is termed as Chaparral in California and Maquis in the Mediterranean area comprises of evergreen often spiny shrubs and low trees between 1 to 5 m high with small thick drought resistant leaves. Since of its relatively dry conditions, these shrub lands are greatly influenced by fire. California Chaparral is highly inflammable. Fires are often started by lightning. In recent times bush fires in this biome have caused so much havoc in both Australia and California.
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