A biome is a large ecological area or region that is characterized by its climate, soil type, and vegetation; the dominant plants and animals that live there. In another words biome is defined as the world’s major communities, classified according to the predominant vegetation and characterized by adaptations of organisms to that particular environment. A biome is determined mainly by its climate-like temperature and rainfall.Each biome has a different climate, which in turn affects the soil.

There are five major categories of biomes on earth. In the five biomes, there are many sub-biomes. The climate and geography of a region determines what type of biome can exist in that region. The major types of biomes are; forest, grassland, tundra, desert and aquatic. In these, Forests are classified into tropical, temperate, and taiga; grasslands are divided into savanna and temperate grasslands; and the aquatic biome is split into freshwater, marine and brackish. Each biome consists of many ecosystems whosecommunities have adapted to the small differences in climate and the environment inside the biomes.

TERRESTRIAL BIOMES

FOREST

A forest may be defined as a large uncultivated tract of land covered with trees of different species growing close together. The conditions such as temperature, ground moisture (rainfall), soil type and topography are responsible for the establishment of forest communities and their distribution. Forests occupy approximately one-third of Earth’s land area. Forests are becoming major casualties of civilization as human populations have increased over the past several thousand years, bringing deforestation, pollution, and industrial usage problems to this important biome. The forest biomes can be classified according to the vegetation, climate and latitude. There are three major types of forests classified according to distributional patterns of plants, world climate and latitude; Tropical, Temperate and Taiga.

1.TROPICAL FOREST

Earth’s most complex land biome is tropical forest in terms of both structure and species diversity. Tropical forests are characterized by the greatest diversity of species.Tropical forests occur near the equator, tropical region, within the area bounded by latitudes 23.5 degrees N and 23.5 degrees S. There are two seasons – rainy and dry. More than ½ of the tropical forests have been already destroyed.

1.1TROPICAL EVERGREEN RAIN FOREST/ EQUATORIAL FOREST.

These forests are found in warm and humid areas. They are having a heavy rainy season, the annual precipitation is above 200 cm and the average temperature is about 20-25⁰C. Normally, it extends between 10⁰N and 10⁰S latitude. While covering less than 6 percent of Earth’s land surface, rain forests are home to more than 50 percent of theworld’s plant and animal species. There is no definite time for trees to shed their leaves, so they are appearing green all the year round. The trees are having an averageheight of 45-60m or even more. Many of the trees have straight trunks that don’t branch out for 100 feet or more. The topsoil of tropical rainforest is heavily leached due to the rain and so poor in nutrients. Due to this regeneration of the tree cover is difficult when it is cleared. Because of these poor nutrients (in the surface), rainforest trees have veryshallow roots to get more nutrients and they are having buttressed trunks to support. 

The tropical evergreen forests are well stratified. They are having a multi-layered continuous canopy; growing in layers; 5 layers. The stratification results from competition between species for favourable locations for the sunlight. First layer: uppermost canopy of the tallest trees. The tall trees grow so close together that their crowns interlock to form a continuous canopy, likes an umbrella or crown which blocks out the sunlight to the next layers. They are in an average height of 30m– 60m. Second layer: This layer is at a height of 25m-30m. Third layer: Have lower and smaller trees, height of 15-20m. Fourth layer: It is the shrub layer, also some stunted plants and trees of less than 5m height are there. Fifth layer: It is the ground layer having herbaceous plants and ferns.

Tropical evergreen rain forest biome accounts for the largest number of plant species.

The flora is highly diverse here; one square kilometer may contain as many as 100 different tree species. Tree is the most significant floral member, second is the Creepers(climbers) like herbaceous plant climber, lianas and epyphytes (they do not need to have their roots on the surface). They are forest of tall and large trees like ebony, mahagony, rosewood, palms; and creepers like vines, lianas, epiphytic orchids; bromeliads, shrubs, herbs, ferns, mosses, etc.

Like the vegetation, animal life in this region is also found in abundance and variety. The most of the animals found are arboreal animals (creatures, which spend the majority of their lives in trees). Some examples of animals in the evergreen forest are howler monkeys, brocket deer, lemur, elephants, one horned rhinoceros, bats, sloth, scorpions, snails, oatimundis, agoutis, curassows, tinamous, plenty of birds, humming birds, butterflies, lizards, silky ant eaters, woolly oppassum, kinkajous, armadillos, jaguars, owls, parrots, parakeets, tree frog, etc.

The primary ecological productivity of the tropical rain forest is the highest of all biome type of the world. It accounts 40 percent of the total net productivity of the world, approximately 5000 dry grams per square meter per year.

They are found in South America, West Africa, Australia, Southern India, and Southeast Asia. The subdivisions of the tropical rains forests are determined by the seasonal distribution of rainfall. And they are:

1.1.1TROPICAL WET EVERGREEN RAIN FOREST

They provide optimum environmental conditions for plant and animal growth; it is characterized by high rainfall (>200cm) and temperature. There is no dry season. The maximum development of this biome has taken place in Amazone Basin (South America), Congo Basin (Africa) and Indo Malaysian Region (mainly in Java, Sumatra, Borneo, Malaysia and Guinea). It is characterised by the forest of tall, straight evergreen trees. The common trees are; mahogony, aini, rosewood, ebony, cinchona, jackfruit, betel nut palm, jamun, mango,etc.

1.1.2TROPICAL SEMI EVERGREEN RAIN FOREST

These are found in the less rainy regions of the equatorial forest, and these forests have a mixture of evergreen and moist deciduous trees. They have somewhat dry season (the upper tree story consists of deciduous trees, while the lower story is still evergreen). The under growing climbers provide an evergreen character to these forests. The main species are white cedar, hollock, kail, etc.

1.2.TROPICAL DECIDUOUS FORESTS

Trees are normally deciduous, because of the dry period summer, during which they shed their leaves to withstand the drought. Normally, it extends between 10⁰ and 25⁰N-Slatitude. They are found in South East Asia, Central and South America, South Eastern USA, South-Eastern and Western Africa, Northern Australia, Southern Brazil,Burma, Taiwan and southern china. These are the most widespread forest in India. They are having a temperature range of 25-30⁰C. They are rich in nutrients than equatorial rain forest. The number of plants species is less in the tropical deciduous forest than the tropical evergreen rainforest. So the number of animal species less than that of the evergreen rain forest. Since the density of plants is lower than the rainforest, there is less competition among plants for getting sunlight, so the trees are of medium height (25-45m). They are occurring in regions where total annual rainfall is about 100cm. This biome has the largest number of domesticated animals, because of the development of agriculture. On the basis of availability of water, they are further divided into:

1.2.1.TROPICAL MOIST DECIDUOUS FOREST:

The trees are tall, with broad and branched trunks and roots to hold them firmly to the ground. Species found in these forests include Sandalwood,Teak, Sal, bamboo, shisham, hurra, mahua, amla, semul, kusum,arjun, mulberry, khair, rosewood, deodar, mango,etc. 

1.2.2.TROPICAL DRY DECIDUOUS FOREST:

As the dry season begins, the trees shed their leaves completely. They are intermediate between moist deciduous and thorn forests. The common trees of these forests are; teak, sal, Tendu, palas, amaltas, bel, khair, axlewood, Sal, Peepal, Neem, a variety of acacia, bamboo, etc.

Tropical deciduous forest has comparatively lesser number of animal species than the rainforest. The main fauna are; lions, tigers, elephants, rhinos, leopards, spotted deer, sambhar, deer, Indian Gazelle, nilgiri antelope, wild boar, pig, huge variety of birds, lizards, snakes, tortoises, etc. 

2.TEMPERATE FORESTS

The forest found in the temperate region, about 48⁰ N latitude. Temperate forests occur in eastern North America, northeastern Asia, and western and central Europe. Well-defined seasons with a distinct winter characterize this forest biome. The temperature ranges from 20 – 30⁰C. Rainfall is evenly distributed throughout the year about an average of75-150cm. The soil is fertile, enriched with decaying litter. It has deep soil layers, rich in nutrients, so is good for agriculture. Climate and amount of sunlight can vary tremendously between each season. Temperate forests have moderately dense broadleaved trees – mostly deciduous & some evergreen; with less diversity of plant species.Trees adapt to varied climate by becoming dormant in winter. Deciduous forest has more diversity than that of coniferous forest, but less diversity of plant species than that of tropical rain forest. Deciduous forests also grow in layers but not as much that of evergreen. More sunlight reaches the ground compared to a rainforest so more ground dwelling plants can see there. The main plant species are Oak, Beech, Maple, hickory, hemlock, basswood, cottonwood, Elm, Willow, spring flowering herbs, etcThe main fauna are; Squirrels, rabbits, skunks, birds, black bears, mountain lions, deer, bobcat, timber wolf, fox, Bald Eagles, raccoon, elks, White tailed deers, coyotes, American buffalos, beavers, wolves, Cougar, owl, rodent, opossum. 

3.TAIGA OR BOREAL FOREST

The taiga is the biome of the needle leaf forest. A lot of coniferous trees grow in the taiga. Cold-tolerant evergreen coniferslike Pine, Fir, Spruce and Larch are the major trees seen here. The roots are long to anchor trees. The needles are long, thin and waxy. Low sunlight and poor soil keeps plants from growing on forest floor. Taiga have a thin soil cover and poor in nutrients and acidic. The seasons are divided into short moist rainy moderately warm summers and long cold snowfall dry winter. They have a very low temperature. The precipitation is mostly snowfall and is ranging 40 – 100 cm. extreme annual variation of temperature ranging between -40⁰C to 25⁰C. The animals are adapted for cold winters. The main fauna are: Caribou, moose, Blackfly, timber wolf, lynx, bears, wolverines, capercaillies, red squirrels, crossbill,pine marten, mink, beaver, woodpeckers, owl, hawks, bears, deer, hares, bats etc. It is also called as temperate coniferous forest, because of a few species of temperate deciduous trees have also developed in this biome. Eg. Aldar, Birch and Poplar.

Boreal forests, or taiga, represent the world’s largest terrestrial biome. Found only in Northern Hemisphere, occurring between 50 and 60⁰ N latitudes just below the tundra biome. And it stretches over Eurasia and North America, parts of Siberia, Alaska, Canada and Scandinavia.

The average net primary productivity is 800 dry grams per square meter per year.

FORESTS IN INDIA

India possesses a distinct identity, not only because of its geography, history and culture but also because of the great diversity of its natural ecosystems. The panorama of Indian forests ranges from evergreen tropical rain forests in the Andaman and Nicobar islands, the western ghats and the northeastern states, to dry alpine scrub high in the Himalayas to the north. India is rich in biodiversity because of its diverse physiography and climatic conditions falls in the confluence of three major biogeographic realms, the Indo-Malayan, Palaearctic and Africotropical. On the basis of certain common features such as predominant vegetation type, climatic regions, soil type, topography and elevation, Indian forests can be divided into the following groups.

1.TROPICAL EVERGREEN FORESTS

These forests are found in the western slope of the Western Ghats, hills of the north-eastern region and the Andaman and Nicobar Islands. Forest found in heavy rainfall areas (more than 200cm) with short dry seasons. It has luxuriant vegetation from trees to creepers. Ebony, mahogany, rosewood, rubber and cinchona are some of the commercially important trees found in these forests. Elephants, monkey, lemur and deer make these forests their habitat. The jungles of Assam and West Bengal house the one horned rhinoceros. Plenty of birds, bats, sloth, scorpions and snails are also found in these rain forests.

• Tropical wet evergreen forest is found in the states; Arunachal Pradesh, Assam, Nagaland, Manipur, Mizoram, Kerala, Karnataka and Tamil Nadu.
• Tropical Semi evergreen forest are found in the states; Assam, Nagaland, Kerala, Karnataka, Goa, Maharashtra, Tamil Nadu and Gujarat.
• Tropical dry evergreen forest are found in the states; Tamil Nadu and Andhra Pradesh.

2. TROPICAL DECIDUOUS FORESTS/TROPICAL MONSOON FOREST

Tropical Deciduous Forests are the most widespread forests of India. They are occurring in regions where total annual rainfall is high, average 70-200cm. They are also called the monsoon forests. The natural vegetation of tropical monsoon regions depends on the amount of the rainfall. They are divided on the basis of water availability. Lion, tiger, pig, deer, elephant are some of animals that make these forests their habitat. A large variety of birds, lizards, snakes and tortoise are also found here.

• TROPICAL MOIST DECIDUOUS FORESTS

The forest getting an average rainfall of 100 – 200cm. Teak trees are the most dominant species of trees found in these forests. Bamboos, sal, shisham, sandalwood, khair, kusum, arjun, mulberry are some of the other commercially important species found here. These are found in the northeastern states along the foothills of Himalayas and eastern slopes of the Western Ghats and middle regions of Andaman and Nicobar islands. They are found in the states; Assam, Meghalaya, Tripura, Mizoram, Manipur, Nagaland, West Bengal, Sikkim, Jharkhand, Bihar, Uttar Pradesh, Uttarakhand, Hariyana, Punjab, Orrissa, Chhattisgarh, Madhya Pradesh, Maharashtra, Telengana, Andhra Pradesh, Kerala, Tamil Nadu, Karnataka, Goa and Gujarat.

• TROPICAL DRY DECIDUOUS FORESTS

These forests are found in the rainier parts of the Peninsular plateau. The area in which rainfall ranges between 70 – 100cm. Teak, Sal, Peepal, and Neem are some of the variety of trees that are found here. Sandalwood is a deciduous tree which generally grows in the dry, deciduous forests of the deccan plateau. It grows almost exclusively in Karnataka, Tamil Nadu, Kerala and Andhra Pradesh. These forest are found in the states; Punjab, Hariyana, Himachal Pradesh, Uttarakhand, Uttar Pradesh, Bihar, West Bengal, Jharkhand, Orissa, Chhattisgarh, Madhya Pradesh, Rajasthan, Madhya Pradesh, Gujarat, Maharashtra, Telengana, Andhra Pradesh, Karnataka and Tamil Nadu. 

3. TROPICAL THORN FORESTS AND SCRUBS

Tropical thorn forests occur in the areas which receive rainfall less than 70 cm. The thorn forests are found in the semi-arid areas. The trees are having a height of 6-10 meters. This forest consists of thorny trees, variety of grasses and shrubs. The trees are scattered and have long roots. Leaves are mostly thick and small to minimize evaporation. The stems of most plants are succulent to conserve water. In these forests, plants remain leafless for most part of the year and give an expression of scrub vegetation. Important species found are babool, ber, and wild date palm, khair, neem,khejri, palas, tussocky grass, Acacias, euphorbias, cacti, spurge, caper, cactus, etc. The common animals are rats, mice, rabbits, fox, wolf, tiger, lion, wild ass, horses and camels, leopard, caracal, chinkara, Chousingha, Blackbucks,etc. These forest are found in the states; Punjab, Hariyana, Uttar Pradesh, Madhya Pradesh, Rajasthan, Gujarat, Maharashtra, Telengana, Andhra Pradesh, Karnataka and Tamil Nadu. 

4. SUB-TROPICAL VEGETATION

They are found in the states; Arunachal Pradesh, Sikkim, Uttarakhand, Uttar Pradesh, Hariyana, Punjab, Himachal Pradesh, Jammu and Kashmir.

5. MONTANE FORESTS

Forest found in the higher altitudes, along the slopes of mountain is called montane forests. They can be classified in to Northern mountain forests and the Southern mountain forests. The Himalayas are the main place where mountain forests can be found in India. The southern slopes of the Himalaya carry thicker vegetation than thenorth facing slopes because of the higher precipitation. In the foothills of Himalayas deciduous forests are there. The montane forest can be classified into Wet temperate, temperate and alpine. In the north India, there are three layers of forests; the higher layer has mainly coniferous, the middle layer has deciduous trees such as the oak and the lowest layer is covered by rhododendron and champa. In the south, it is found in parts of the Nilgiri Hills, the higher reaches of Kerala. 

• MONTANE WET TEMPERATE FORESTS

These are found in the east of Nepal into Arunachal Pradesh. They are getting a minimum rainfall of 200cm. Wet temperate type of forests is found between a height of1000 and 2000m, in the higher hill ranges of northeastern India. Trees that are predominant in these forests are broad-leafed oak trees and chestnut trees. Montane wet temperate forest found in the states; Arunachal Pradesh, Nagaland, Assam, Tamil Nadu, Karnataka and Kerala.

• MONTANE MOIST AND DRY TEMPERATE FORESTS WITH GRASS LANDS

Temperate Forests can be found at a height of 1500 to 3000 metres. Coniferous trees like pine (chir pine), deodar, chinar, walnut, Blue pine, laurel spruce, silver fir, cedar, oak, maple, are found here. These forests cover mostly the southern slopes of the Himalayas. They are also found in places of high altitude in southern and northeast India.

Himalayan moist Temperate forestare found in the states; Sikkim, Uttarakhand, Himachal Pradesh, Jammu and Kashmir.

Himalayan Dry Temperate forest are found in the states; Himachal Pradesh and Jammu and Kashmir. 

•   ALPINE FORESTS

Alpine Forests are found at high altitudes, generally more than 3,600m above sealevel. Silver fir, junipers, pines, birch, rhododendrons, etc are the common trees of these forests. These tree layers progressively merge into the alpine grassland to the higher. Above that higher altitude, mosses and lichens form part of the tundra vegetation. The alpine and sub alpine forest are found in the states; Arunachal Pradesh, Sikkim, Uttarakhand, Himachal Pradesh and Jammu and Kashmir.

The common animals found in the Montane forests are Kashmir stag, spotted dear, wild sheep, jack rabbit, Tibetan antelope, yak, snow leopard, squirrels, shaggy horn wild ibex, bear, rare red panda, sheep and goats with thick hair.

The southern mountain forest are those in three distinct areas of Peninsular India; Western ghats, the Vindhyas and the Nilgiris. They are having a temperate vegetation in the higher regions and subtropical in the lower regions of the western ghats, especially in Kerala, Tamil Nadu and Karnataka. The temperate forests are called sholas in nilgiris, anaimalai and palani hills. The main flora found here are magnolia, laurel, cinchona and wattle.

6. LITTORAL AND SWAMP FOREST

These are the vegetation situated on the shore of the sea or a lake or an area of low-lying, uncultivated ground where water collects; a bog or marsh.The soil is formed of silt, silt-loam or silt-clay and sand. The plants in the mangrove forest are typical halophytes which are characterized by presence of prop roots with well-developed knees for support and pneumatophores and viviparous germination of seeds. The common trees of these forests are Rhizophora, Avicennia, Sundari, Palm, Cocunut, Keora, Agar etc. The mangroves have roots that consist of soft tissue so that the plant can breathe in the water. The roots of mangrove trees get submerged under water. These type forests are found along the Andaman and Nicobar Islands and the deltas of the Ganga and the Brahmaputra. Other areas are Mahanadi, the Godavari and the Krishna deltas. The best development occurs in Sundarbans, the largest mangrove forest -is home to many rare and globally threatened wildlife species such as the estuarine crocodile (Crocodilus porosus), gharial, royal Bengal tiger (Panthera tigris), Water monitor lizard (Varanus salvator), Gangetic dolphin (Platinista gangetica), and olive ridley turtle (Lepidochelys olivacea), Indian python, etc. The states having littoral and swamp forest are; West Bengal, Orissa, Andhra Pradesh, Tamil Nadu and Gujarat.

 GRASS LANDS

Grassland biomes are large, lands of grasses, flowers and herbs. Latitude, soil and local climates for the most partdetermine what kinds of plantsgrow in particular grassland. Therainfall is less here, that not enough to support a forest, but it is more than that of the desert. Due to the less precipitation, drought and fire prevent large forests from growing. The soil of most grassland is also too thin and dry for trees to survive. Grassland biomes can be found in the middle latitudes, in the interiors of continents. There are two real seasons: a growing season and a dormant (not growing-too cold) season. There are mainly two types of grassland biomes; Tropical (savanna) and temperate grasslands. 

1.SAVANNA (TROPICAL GRASSLANDS)

It is a variety of grassland with scattered shrubs and individual isolated trees (deciduous). The trees are having a flat crown, umbrella shaped. Savanna can be foundbetween tropical deciduous rainforest and desert biome. Savanna is found in the tropics, near equator. Savannas cover Africa (generally central and east Africa) and large areas of Australia, South America (Venezuela, Brazil, Columbia), and India.

Climate is the most important factor in creating a savanna. Savannas are always found in warm hot climates where the annual rainfall is from about 50 – 125 cm per year.It has only 2 very different seasons; A dry and warm one (the fire’s season) and a rainy (wet) hot one. In tropical grasslands the length of the growing season is determined by how long the rainy season lasts. Amount of precipitation supports tall grasses but only occasional trees. It appears greenish and well-nourished in the rainy season and turns in toyellow in dry season. The soil has porous with a thin layer of humus (the organic portion of soil created by partial decomposition of plant or animal matter), which provides vegetation with nutrients. Savanna contains the greatest number of grazing animals on Earth. Plants of the savannah are highly specialised to the long period of drought. They have long tap roots, thick barks to resist annual fire, trunks that can store water, and the leaves that can drop off during the dry season to conserve water. Many plants havethorns and sharp leaves to protect against predation. The main floras are Acacia, baobab, bottle trees, grass, etc

Most of the animals on the savannah have long legs or wings for long migrations. The animals are adapted for short rainy season, they migrate as necessary. They reproduce during rainy season and ensure more young survive. The fauna are Hawks, buzzards, Kangaroo, Giraffes, zebras, buffalos, elephants, antelopes, gazells, marsupials, guanaco, mice, moles, snakes and worms, Lion, leopards, cheetah, jackals, hyenas, gophers, ground squirrels, termites, beetles, ostrich, etc. Average net primary productivity is 900 dry grams per square meter per year

2.TEMPERATE GRASSLANDS

Temperate grasslands are characterized as having grasses as the dominant vegetation. Trees and large shrubs are absent. Temperate grasslands have hot summers and cold winters. The amount of rainfall is less in temperate grasslands than in savannas. The annual average is about 50-90cm. The amount of annual rainfall influences the height of grassland vegetation, with taller grasses in wetter regions.In the temperate grasslands the length of the growing season is determined by temperature.

The soil of the temperate grasslands is deep and dark, with fertile upper layers. The rotted roots hold the soil together and provide a food source for living plants. Some non-woody plants, specifically a few hundred species of flowers, grow among the grasses. The various species of grasses include purple needlegrass, blue grama, buffalo grass, and galleta. Flowers include asters, blazing stars, coneflowers, goldenrods, sunflowers, clovers, psoraleas, and wild indigos.

The appearance of the temperate grasslands varies with seasons. In spring, the grass appear, green, fresh and blooming with small, colourful flowers. The light rainfall that comes in late spring and early summer greatly stimulates their growth and there is plenty for the animals to graze. In summer, there is so much heat and evaporation that the grass is scorched. The bluish-green grass turns yellow and soon brown. Towards autumn, the grass withers and dies, but the roots remain alive and lie dormant throughout the cold winter. The average net primary productivity is 600 dry grams per square meter per year.

The fauna found here are gazelles, zebras, rhinoceroses, wild horses, lions, wolves, prairie dogs, jack rabbits, deer, mice, coyotes, foxes, skunks, badgers, blackbirds, grouses, meadowlarks, quails, sparrows, hawks, owls, snakes, grasshoppers, leafhoppers, and spiders.

The temperate grass lands are found in South Africa, Hungary, the pampas of Argentina and Uruguay, the steppes of the former Soviet Union, and the plains and prairies ofcentral North America. Temperate grasslands can be further subdivided; prairies and steppes. They are somewhat similar. Prairies are grasslands with tall grasses about 11 feet.

STEPPES

The Steppe biome is a dry, cold, grassland that is found in all of the continents except Australia and Antarctica. It is mostly found in the USA, Mongolia, Siberia, Tibet and China. Steppes occur in the interiors of North America and Europe. There isn’t much humidity in the air because Steppe is located away from the ocean and close to mountain barriers. The Steppe biome is usually found between the desert and the forest. Steppe has warm summers and really cold winters. All the Steppes experience long droughts and violent winds due to few trees. The steppe is differing only in the density and quality of the grass. Their greatest difference from the tropical savanna is that they are practically treeless and the grasses are much shorter. The grasses are greater than 30cm tall. They include blue grama and buffalo grass, cacti, sagebrush, spear grass, and small relatives of the sunflower.

DESERT

These are the driest places on earth. Deserts cover about one fifth of the Earth’s surface and occur where rainfall is less than 25cm. Evaporation rates regularly exceed rainfall rates. The environment, so lacking in moisture and so excessive in heat, is most unfavourable for plant growth. Desert soil is rich in nutrients with little or no organic matter. Even though nutrients are present in the soil due to the less rainfall the productivity is less.Most desert shrubs have well-spaced long roots to gather moisture, and search for ground water. Plants have few or no leaves and are either waxy, leathery, hairy or needle-shaped to reduce the loss of water through transpiration. Some of them are entirely leafless, with pricks or thorns. Others like the cacti have thick succulent stems to store up water for long droughts.Major deserts on earth: sahara, thar, Kalahari, Arabian, namib, Iranian, Turkestan, takia makan gobi, Australian, Patagonian, Atacama, north American. Desert Biomes can be classified as follows:

1.HOT AND DRY DESERT

In this types of deserts seasons are generally warm throughout the year and very hot in the summer. The winters usually bring little rainfall. The average rainfall is less than 1.5cm.Some years are even rainless. Inland Sahara also receives less than 1.5 cm a year. The mean annual temperature range is 20-45⁰C. Most Hot and Dry Deserts are near the Tropic of Cancer or the Tropic of Capricorn. Eg. Sahara, Kalahari, Marusthali, Rub-el-Khali. The four major North American deserts of this type are the Chihuahuan, Sonoran, Mojave and Great Basin.

The plants need some adaptations to survive. Some of them are the ability to store water for long periods of time and the ability to stand the hot weather. Plants are mainlyground hugging shrubs, the leaves are with water conserving characteristics. Some examples of plant are Turpentine Bush, Prickly Pears, and Brittle Bush, yuccas, ocotillo, false mesquite, sotol, ephedras and agaves. The animals include small nocturnal (active at night) animals. Some examples of the animals are Borrowers, kangaroo rats, Mourning Wheatears, and Horned Vipers.

2.SEMI ARID DESERT

Semi-arid desert are found in the marginal areas of hot deserts. They are having a temperature of 21-38⁰C. The summer is moderately long and dry, like hot deserts. The winters normally bring low concentrations of rainfall. The average rainfall ranges from 2-4 cm annually. Semiarid plants include: Creosote bush, bur sage, white thorn, cat claw, mesquite, brittle bushes, lyciums, and jujube. The animals include the kangaroo rats, rabbits, and skunks; lizards and snakes; burrowing owls and the California thrasher. The major deserts of this type include the sagebrush of Utah, Montana and Great Basin. They also include the North America, Newfoundland, Greenland, Russia, Europe and northern Asia.

3.COSTAL DESERT

These deserts occur in moderately cool to warm areas. A good example is the Atacama of Chile. The temperature range is 15-35⁰C. The cool winters of coastal deserts are followed by moderately long, warm summers. The average rainfall measures 8-13 cm in many areas. The plants living in this type of desert include the salt bush, buckwheat bush, black bush, rice grass, little leaf horsebrush, black sage, and chrysothamnus. Animals include: coyote, badger, toads, great horned owl, golden eagle, bald eagle, lizards, snakes, insects etc.

4.COLD DESERT

They are found near to the tundra regions. Cold deserts are near the Arctic part of the world. The temperature range is 2-25⁰C. These deserts are characterized by cold winters with snowfall and high overall rainfall. The precipitation is of 15-26cm. They have short, moist, and moderately warm summers. The animals in Cold Deserts also have to burrow but in this case to keep warm, not cool. Widely distributed animals are jack rabbits, kangaroo rats, kangaroo mice, pocket mice, grasshopper mice, and antelope ground squirrels, badger, kit fox, and coyote.

TUNDRA

The word tundra means a barren land. The ground is permanently frozen 25-100cm down so that trees can’t grow there. The tundra is the world’s coldest and driest biomes. They have little precipitation, poor nutrients, short growing seasons and low biotic diversity. Temp rarely higher than 10⁰C. They are bitterly cold and covered with snowand ice. They have short growing seasons. Very short warm season that is very wet.Many insects are there during warm season. Below a thin layer of tundra soil is itspermafrost, a permanently frozen layer of ground.

Only certain small plants such as mosses, shrubs, sedges, lichens, and grasses can grow. The plants here are growing close to the ground. And they are having shallow roots to absorb the limited water resources.

The animals are shrews, hares, rodents, wolves, arctic foxes, polar bears, lemmings, wolverine, reindeer, deer, harp seal, penguins of Antarctica, muskox. Black flies, deer flies, mosquitoes and noseeums (tiny biting midges) can make the tundra a miserable place to be in the summer. Migratory birds like the harlequin duck, sandpipers andplovers are found in tundra. The average net primary productivity is 140 dry grams per square meter per year. Tundra Biomes can be classified as follows:

1.ARCTIC TUNDRA

Arctic tundra is located in the northern hemisphere, encircling the North Pole. The growing season ranges from 50 to 60 days. The average winter temperature is -34°C. The average summer temperature is 3-12°C which enables this biome to sustain life. Yearly precipitation, including melting snow, is 15 to 25 cm. There isno deep root system of vegetation. They are having low shrubs, sedges, reindeer mosses, liverworts, grasses, 400 varieties of flowers, crustose and foliose lichen. The animals are: lemmings, voles, caribou, arctic hare, squirrels, arctic foxes, wolves, polar bears, Migratory birds: ravens, snow buntings, falcons, loons, sandpipers, terns, snow birds, gulls. It occupies the northern fringe of Canada, Alaska, European Russia, Siberia and island group of Artic Ocean.

2.ALPINE TUNDRA

Alpine tundra is located on mountains throughout the world at high altitude, above the tree line and just below the snow line of the mountain. In the summer average temperature ranges from 10-15⁰C. In the winter the temperature are below freezing. The winter season can last from October to May. The summer season may last from June to September. The growing season is approximately 180 days. The major vegetation’s are tussock grasses, dwarf trees, small-leafed shrubs, heaths. Animals living arepikas, marmots, mountain goats, sheep, elk, grouselike birds, springtails, beetles, grasshoppers, butterflies, etc

Alpine animals have to deal with two types of problems; the cold and too much high UV rays. This is because there are fewer atmospheres to filter UV rays from the sun light. There are only warm blooded animals in the Alpine biome. Alpine animals adapt to the cold by hibernating, migrating to lower warmer areas, or insulating their bodies with layers of fat. Alpine animals also have larger lungs, more blood cells and hemoglobin because of the increase of pressure and lack of oxygen at higher altitudes.

BIOGEOGRAPHY

Biogeography is the study of the geographical distribution of plants and animals. Most species of plants and animals of the world are essentially restricted in their distribution either by natural barriers or because of the history of their origins and dispersal. The major units of distribution are referred to as bio-geographical regions. These major global units of biogeography were first recognized by P.L.Sclater (1858, in J. Proc. of Linn. Soc.2), and later elaborated upon and described in modern terms as “realms” by P.J.Darlington (1957,in Zoogeography. John Wiley & Son. New York).

Biological regions or “Biogeographical Realms” are defined by climate, altitude and terrain (geography) which have acted upon the evolutionary process to give rise to certaindistinctive life forms. Biogeography, therefore, refers to this specific and distinctive community of plants and animals (biological community) occupying a specific geographical region. Biogeographic realms are large spatial regions within which ecosystems share a broadly similar biological evolutionary history. Eight terrestrial biogeographic realms are there on earth. Each region is then subdivided into faunal or vegetational zones that mean biogeographic zone; it again divided in to biogeographic provinces. India belongs to the Indo-Malayan Realm. The country has 10 different biogeographic zones and 26 biotic provinces. The biogeographic realms are; Palaearctic Realm, Nearctic Realm, Africotropical Realm, Indo-Malayan Realm, Oceanian Realm, Australian Realm, Antarctic Realm and Neotropical Realm.

Table.1 Biogeographic zones and provinces in India

Table. 2. Biomes and Productivity