Climate is the characteristic condition of the atmosphere near the earth’s surface at a certain place on earth. It is the long-term weather of that area (at least 30 years). This includes the region’s general pattern of weather conditions, seasons and weather extremes like hurricanes, droughts, or rainy periods. Two of the most important factors determining an area’s climate are air temperature and precipitation.
|Western Margin||Central Continent||Eastern Margin|
|Cold Zone||Arctic or Polar Types||65* – 90* Latitude|
|Cool Temperate||British type||Siberian type||Laurentian type||45* – 65* Latitude|
|Warm Temperate||Mediterranean||Steppe type||China type||30* – 45* Latitude|
|Hot Zone||Hot Desert||Sudan type||Monsoon type||10* – 30* Latitude|
|Equatorial Zone||Hot Wet Equatorial Climate||0* – 10* Latitude|
Natural Vegetation of the World
World biomes are controlled by climate. The climate of a region will determine what plants will grow there, and what animals will inhabit it. All three components, climate, plants and animals are interwoven to create the fabric of a biome.
Hot Wet Equatorial Climate
- Equatorial hot, wet climate is found between 5* – 10* north & south of the equator mostly viz.
- the Amazon Basin (South America)
- the Congo Basin (Africa)
- The most outstanding feature of the equatorial climate is its great uniformity of temperature throughout the year with no winters.
- The average monthly temperatures are about 26 – 28 degrees Celsius, with small annual range of temperature ~ 3*C & fairly greater diurnal range of temperature ~ 12* – 15*C.
- Cloudiness and heavy precipitation ~ 150 – 250 cm of rainfall or more in a year, helps to moderate the temperature, so that even at the equator, climate is not unbearable.
- There is no month without the rain & a distinct dry season like that of savanna or tropical monsoon climate is absent.
- Most of the rainfall is convectional, with thunderstorm & lightening often accompanying the torrential showers.
- The convection uplift is related to the position of the ITCZ and rainfall totals double when the sun is directly overhead at the spring and autumn equinox, with the least rain falls at June & December solstices.
- Besides the convectional rainfall, mountainous regions also experience much orographic or relief rainfall
- In addition, there are some intermittent showers from cyclonic atmospheric disturbances caused by the convergence of air masses at Doldrums.
- The relative humidity is constantly high ~ over 80 %, making one feel sticky & uncomfortable
Vegetation in Equatorial Regions
- The year round high temperatures and abundant rainfall in equatorial regions support a luxuriant type of vegetation – Tropical or equatorial rain forests.
- In the Amazon lowlands, the forest is so dense & extravagance that a special term Selva is used to describe it.
- Unlike the temperate regions, the growing seasons here is all year round
- Seeding, Flowering, Fruiting & Decaying do not take place in seasonal pattern, so some trees may be flowering while others only a few yards away may be bearing fruits.
- There is neither drought nor cold to check the growth in any part of the year.
- Unlike the temperate forests, many different types of trees and other plants can be found growing in a relatively small area of rainforest.
- Rainforests cover only about 6 % of the Earth’s surface.
- However, they contain about half of the world’s known animal species and provide about 40% of the world’s oxygen.
- Equatorial vegetation comprises a multitude of evergreen trees that yields tropical hardwood viz. Mahogany, Ebony, Greenheart, Cabinet Woods & Dyewoods.
- There are smaller palm trees, climbing plants like lianas & epiphytic & parasitic plants that live on other plants.
- Under the trees grow a wide variety of ferns, orchids & lalang (tall grass)
- There are several layers of vegetation in a rainforest with all plants struggling to move upward to get sunlight.
- The uppermost layer is made up of the crowns of the tallest trees with average height 45 – 60 meters are known as emergent, with their crowns exposed to the direct sunlight.
- The next layer is known as the canopy with an average height of about 20 to 40 meters.
- The crowns of the trees in this layer are tightly packed together forming a nearly unbroken cover for the forest floor.
- If you were looking down on a section of the rainforest from above, you would not be able to see the ground because of the cover provided by the canopy, very little sunlight reaches the lower layers of the rainforest.
- Below the canopy is another layer known as the understory with trees only few meters high.
- Here one can find trees which only grow to about 15 meters at maturity as well as young saplings which will eventually grow to reach the canopy. Sunlight here is limited.
- Between understory & the forest floor lays the shrub layer, composed of ferns & shrubs.
- Only about 1% or 2% of sunlight reaches this layer.
- Therefore, only few plants are able to thrive there which must be able to tolerate low light conditions.
- In order to support their great height, many trees have buttress roots(also called plank buttresses) which extend above the ground and along the trunk on all sides.
- Some plants in the lower layers of the rainforest have verylarge leavesin order to make efficient use of the little sunlight which reaches them.
- Some plants, known as lianas, are vines which are rooted in the soil and grow up the trunks of trees all the way into the canopy where their leaves can get more sunlight.
- Some plants, known as epiphytes, grow on trees (their roots are not in the soil).
- They do not harm the trees and they do not get their nutrients from them. They only use the trees for physical support.
- There are other plants which are parasites.
- They grow on other plants and get their nutrients from them, damaging them as they do so.
- There are other plants known as strangler figs.
- They start out by growing on a host tree, and then they grow long roots down the trunk of the tree and into the soil.
- These roots grow larger and begin to surround the trunk of the host tree.
- Eventually the host tree will die, leaving the strangler fig in its place.
- Many parts of the virgin tropical rainforests have been cleared either for lumbering or shifting cultivation.
Life & Development in Equatorial Regions
- The equatorial regions are generally sparsely populated with shifting cultivation as major agricultural practice
- Major crops being manioc (tapioca), yams, maize, bananas & groundnuts
- Food is abundant in form of animals, birds, fishes, fruits, nuts & other jungle produces.
- In the Amazon basin, Indian tribes collect rubber and in the Congo basin Pygmies gather nuts.
- Certain high value industrial crops for which equatorial climate suits best are grown now a days such as rubber, cocoa, oil palms, coconuts, sugarcane, coffee, tea etc.
- Home country of discovery of rubber, Brazil (Amazon basin) exports no natural rubber due to tree diseases & lack of commercial organizations of Indian at Amazon lowlands.
- Currently, Malaysia & Indonesia are leading producers of rubber in the world.
- Cocoa is cultivated most extensively in West Africa with two most important producers Ghana & Nigeria.
- From the same area another crop, oil palms have done equally well.
- Under the conditions of excessive heat & high humidity, man is subjected to physical & mental handicap
- One loses vigour in such an enervating environment along with high exposer to sun strokes, malaria & yellow fever.
- The hot, wet climate which stimulates rapid plant growth also encourages the spread of pest & insects
- Germs & bacteria are most easily transmitted through moist air; which are injurious to all man, animals & plants.
Hardwood & Livestock
- Jungle is so luxuriant that it is quite a problem to clear small patches in it & even difficult to maintain it.
- Lalang & thick grass springs up as soon as shade trees are cut & unless they are weeded at regular intervals, they may choke crops & overwhelm estates.
- Roads & railways constructed through the equatorial lands have to cut through forests & those who maintain them encounter wild animals, snakes & insects
- Once they are completed, they have a high maintenance cost.
- Therefore, many remote parts of Amazon basin & Congo are without modern communications, with rivers as only natural highways.
- Though the tropics have great potential in timber resources, commercial extraction is difficult as trees do not occur in homogeneous stands
- Have no frozen surface to facilitate logging & tropical hardwoods are sometimes too heavy to float in the rivers, even if these flow in desired direction.
- Livestock farming is greatly handicapped by an absence of meadow grass
- Bullocks which are domesticated yields milk & beef well below than those in temperate grasslands.
In its virgin state, due to heavy leaf fall & decomposition of leaves by bacteria, a thick mantle of humus makes the soil fairly fertile, but once the humus content is used after shifting cultivation & natural vegetative cover is removed, the torrential downpour soon wash out most of the soil nutrients. Therefore, soil deteriorates rapidly with subsequent soil erosion.