Natural vegetation refers to a plant community that has been left undisturbed over a long time, so that it could adjust itself to climate and soil conditions as fully as possible.
Due to a diverse geographical and climatic condition, an extensive range of natural vegetation grows in India. According to state records, the forest area covers 23.28 per cent of the total land area of the country.
Himalayan heights are marked with temperate vegetation; the Western Ghats and the Andaman Nicobar Islands have tropical rain forests, the deltaic regions have tropical forests and mangroves; the desert and semi desert areas of Rajasthan are known for cacti, a wide variety of bushes and thorny vegetation.
On the basis of certain common features, the natural vegetation of India can be divided into 5 main types and 16 sub-types as given below.
1) Moist Tropical Forests
1.1) Tropical Wet Evergreen (Rain Forests)Tropical wet evergreen forests are found in the western side of the Western Ghats, some regions in the Purvanchal hill and in the Andaman and Nicobar Islands.
In these areas the annual rainfall exceeds 250 cm, temperature is about 25°-27°C with high humidity (77 percent) and dry season is distinctly short.
These plants do not shed their leaves together and are Mesosphytic in nature, Mesophytic environments are marked by average to hot temperatures and soil that is neither too dry nor too wet.
The trees often reach 45 - 60 metres in height, the sun light cannot reach the ground due to thick canopy. The undergrowth is formed mainly of bamboos, ferns, climbers, orchids, etc.
The timber of these forests is fine-grained, hard and durable with high commercial value - but it very challenging to exploit it due to dense undergrowth and lack of transport facilities.
The important species of these forests are mahogany, ebony, rosewood, mesua, white cedar, jamun, canes, bamboo etc.
1.2) Tropical Semi-EvergreenTropical Semi-Evergreen forests are transitional forests between tropical wet evergreen forests and tropical deciduous forests. These forests are found in western coast, Assam, Lower slopes of the Eastern Himalayas, Odisha and Andamans.
In these areas the annual rainfall lies between 200-250 cm, temperature is about 24°-27°C with high humidity (75 percent) and dry season is not as short as in tropical evergreen forests.
The timber of these forests is similar to that in tropical evergreen forests except that these forests are less dense and timber industry here is better than in evergreen forests.
The important species are laurel, rosewood, mesua, thorny bamboo, white cedar, Indian chestnut, champa, mango, etc.
1.3) Tropical Moist DeciduousTropical Moist Deciduous forests belt run along the Western Ghats surrounding the belt of evergreen forests, a strip along the Shiwalik range including terai and bhabar, Manipur and Mizoram, hills of eastern Madhya Pradesh and Chhattisgarh, Chota Nagpur Plateau, most of Odisha, parts of West Bengal and Andaman and Nicobar islands.
In these areas the annual rainfall lies between 100-200 cm, temperature is about 27°C with high humidity (60-75 percent) and summer are dry.
These trees drop their leaves during the spring and early summer when sufficient moisture is not available.
These forests occupy a much larger area than the evergreen forests but large tracts under these forests have been cleared for cultivation.
The main species found in these forests are teak, sal, shisham, laurel, rosewood, sandalwood, amla, jamun, bamboo, etc.
1.4) Littoral and SwampLittoral and Swamp forests occur in and around the deltas, estuaries and creeks prone to tidal influences (delta or tidal forests).
Littoral forests occur at several places along the coast and Swamp forests are confined to the deltas of the Ganga, the Mahanadi, the Godavari, the Krishna and the Cauvery.
The most pronounced and the densest of these type of forests is the Sunderban in the Ganga delta where the predominant species is Sundri (Heriteera).
The country's wetlands have been grouped into eight categories:
1) Reservoirs of the Deccan Plateau in the south together with the lagoons and other wetlands of the southern west coast.
2) The vast saline expanses of Rajasthan, Gujarat and the Gulf of Kachchh.
3) Feshwater lakes and reservoirs from Gujarats through Rajasthan (Keoladeo National Park) and Madhya Pradesh.
4) The delta wetlands and lagoons of India's east coast (Chilika Lake).
5) The freshwater marshes of the Gangetic Plain.
6) The floodplains of the Brahmaputra, the marshes and swamps in the hills of northeast India and the Himalayan foothills.
7) The lakes and rivers of the mountain region of Kashmir and Ladakh.
8) The mangrove forest and other wetlands of the island arcs of the Andaman and Nicobar Islands Mangroves grow along the coasts in the salt marshes, tidal creeks, mud flats and estuaries.
The important species found in these forests are Sundri, agar, rhizophora, screw pines, canes and palms, etc.
2) Dry Tropical Forests
2.1) Tropical Dry EvergreenTropical Dry Evergreen forests are found along the coasts of Tamil Nadu. These forests get most of their rainfall (100 cm) from the north-east monsoon winds in October - December.
The mean annual temperature of these areas is about 28°C and mean humidity is about 75 per cent.
These forests consists of short statured trees, up to 12 m high, with complete canopy. The growth of evergreen forests in areas of such low rainfall is a bit strange.
The important species are jamun, tamarind, neem, etc.
2.2) Tropical Dry DeciduousTropical Dry Deciduous forests occur in an irregular wide strip running from the foot of the Himalayas to Kanniyakumari except in Rajasthan, Western Ghats and West Bengal.
These forests gets an annual rainfall of 100-150 cm, have closed but uneven canopy and enough light reaches the ground to permit the growth of grass and climbers.
These forests are similar to moist deciduous forests and shed their leaves in dry season, the major difference is that they can grow in areas of comparatively less rainfall.
The important species are teak, axlewood, rosewood, common bamboo, red sanders, laurel, satinwood, etc.
2.3) Tropical Thorn ForestsTropical Thorn forests occur in Rajasthan, south-western Punjab, western Haryana, Kachchh and neighbouring parts of Saurashtra. These forests also grow on the leeside of the Western Ghats covering large areas of Maharashtra, Karnataka, Telangana, Andhra Pradesh and Tamil Nadu.
In these areas the annual rainfall is less than 75 cm, temperature is about 25°-30°C with less humidity (< 50 percent).
The trees of Tropical Thorn forests are very low (6 to 10 metres maximum) and widely scattered.
The important species are babool, ber, and wild date palm, khair, neem, khejri, palas, etc.
3) Montane Sub-Tropical ForestsMontane ecosystems are found on the slopes of mountains.
The subtropical zones or subtropics are geographic and climate zones located to the north and south of the tropical zone. They cover the latitudes approximately between 23.5° and 35° in the northern and southern hemisphere.
3.1) Sub-tropical broad-leaved Hill ForestsSub-tropical broad-leaved Hill forests are found in Eastern Himalayas at altitudes varying from 1000 to 2000 m. and in the Nilgiri and Palni hills at 1070-1525 metres above sea level.
These forests are also found in parts of the Western Ghats such as Mahabaleshwar, the summits of the Satpura and the Maikal Range, highlands of Bastar and Mt. Abu in the Aravali Range.
In these areas the annual rainfall lies between 75-125 cm, temperature is about 18-21°C with high humidity (80 percent).
Commonly found species are evergreen oaks, chestnuts, ash, beech, sals and pines.
3.2) Sub-tropical Moist Pine ForestsSub-tropical Moist Pine Forests are found in Western Himalayas at elevations between 1000 to 2000 metres above sea level and in some hilly regions of Arunachal Pradesh, Manipur, Naga Hills and Khasi Hills.
Commonly found species are: Chir or Chil.
3.3) Sub-tropical Dry Evergreen ForestsSub-tropical Dry Evergreen forests are found in the Bhabar, the Shiwaliks and the western Himalayas up to about 1000 metres above sea level.
These areas get annual rainfall between 50-100 cm in December-March. The summers are sufficiently hot and winters are very cold.
They have low scrub forest with small evergreen stunted trees and shrubs. The most predominant species are Olive, acacia modesta and pistacia.
4) Montane Temperate ForestsMontane ecosystems are found on the slopes of mountains.
Temperate forests are characterized as regions with high levels of precipitation, humidity, and a variety of deciduous trees.
4.1) Montane Wet Temperate ForestsMontane Wet Temperate forests grows at a height of 1800 to 3000 m above sea level in Higher hills of Tamil Nadu and Kerala and in the Eastern Himalayan region.
In these areas the annual rainfall is between 150 cm to 300 cm, temperature is about 11°C to 14°C and humidity is over 80 per cent.
These are closed evergreen forests with large girth trunks, branches are clothed with mosses, ferns and other epiphytes. These trees rarely achieve a height of more than 6 metres.
Important species are: Deodar, Chilauni, Indian chestnut, birch, plum, machilus, cinnamomum, litsea, magnolia, blue pine, oak, hemlock, etc.
4.2) Himalayan Moist Temperate ForestsHimalayan Moist Temperate forests occurs in the temperate zone of the Himalayas between 1500 and 3300 metres, covering the entire length of this mountain range in Kashmir, Himachal Pradesh, Uttarakhand, Darjeeling and Sikkim.
These forests are mainly composed of coniferous species, trees are 30 to 50 m high. The trees are high but fairly open forest with shrubby undergrowth including oaks, rhododendrons and some bamboos.
Most important trees are: Pines, cedars, silver firs, spruce, etc.
Annual rainfall varies from 150 cm to 250 cm.
4.3) Himalayan Dry Temperate ForestsHimalayan Dry Temperate forests are found in the inner dry ranges of the Himalayas where south-west monsoon is very feeble. Such areas are in Ladakh, Lahul, Chamba, Kinnaur, Garhwal and Sikkim.
Precipitation is below 100 cm and is mostly in the form of snow.
Main trees are: deodar, oak, ash, olive, etc.
5) Alpine ForestsAlpine climate is the climate which causes trees to fail to grow due to cold. In India Alpine Forests are found between 2,900 to 3,500 m above sea level.
Alpine Forests can be divided into: (1) sub-alpine; (2) moist alpine scrub and (3) dry alpine scrub.
Alpine forests are characterised by silver fir, junipers, pines, rhododendron and birches trees. The south-west monsoon here is very feeble and the rainfall is below 100 cm, mostly snow.
Lichens and mosses are found in the natural vegetation at higher altitudes.
It is a mixture of coniferous and broad-leaved trees in which the coniferous trees attain a height of about 30 m while the broad leaved trees reach only 10 m.
Deciduous forestA deciduous forest is a biome dominated by deciduous trees which lose their leaves seasonally. The Earth has temperate deciduous forests, and tropical and subtropical deciduous forests, also known as dry forests. Another name for these forests is broad-leaf forests because of the wide, flat leaves on the trees.
Tropical Deciduous Forests are the most widespread forests in India, they are also called the monsoon forests.