Flora refers to plants of a particular region or period, listed as a species and considered as a group. Likewise, fauna refers to the animal life, considered collectively, of any given period, environment or region.

Vegetation, on the other hand, refers to the assemblage of plant species in a given environmental frame or ecological frame. It is broader than the term flora which refers to species composition. Further:

• Natural vegetation includes that part of the plant life which grows in wild without human aid and adapts to constraints of the natural environment in size, structure and requirements. Thus cultivated crops and fruit orchards form a part of the vegetation but not natural vegetation.
• That part of natural vegetation which has remained undisturbed by humans is referred to as virgin vegetation. It can be found in India in the inaccessible parts of the Himalayas, the Thar Desert and the Sunderbans. Elsewhere, human occupation has either transformed natural vegetation into cultivated vegetation or degraded the natural vegetation.
• The virgin vegetation, which is purely Indian is known as endemic or indigenous species but that which has come from outside India is termed as exotic.

Forest: The term forest implies ‘natural vegetation’ of the area, existing from thousands of years and supporting a variety of biodiversity, forming a complex ecosystem.

Depending on the physical, geographical, climatic and ecological factors, there are different types of forests like evergreen forest (mainly composed of evergreen tree species i.e. species having leaves all throughout the year) and deciduous forest (mainly composed of deciduous tree species i.e. species which lose their leaves during particular months of the year). Each forest type forms a habitat for a specific community of animals that are adapted to live in it.

Various factors which influence the type and distribution of natural vegetation and wildlife:

• Land

The nature of land affects the natural vegetation directly and indirectly. E.g. the type of vegetation in the mountainous regions is different than that in the plateau and plain areas. The fertile land is generally devoted to agriculture, while the undulating and rough terrains are areas where grassland and woodlands develop and give shelter to a variety of wildlife.

• Soil

Different types of soils provide basis for different types of vegetation. The sandy soils of the desert support cactus and thorny bushes while wet, marshy, deltaic soils support mangroves and deltaic vegetation. The hill slopes with some depth of soil have conical trees.

• Temperature and Humidity

Temperature and humidity are the main factors which determine the character and extent of vegetation. E.g. an area with high temperature and high humidity supports evergreen forest, while an area with high temperature and low humidity supports thorny bushes (desert).

• Precipitation

Areas of heavy rainfall have more dense vegetation as compared to other areas of less rainfall.

See the following diagram to understand the combined effect of temperature and annual precipitation on the vegetation type of an area:

• Photoperiod (Sunlight)

Photoperiod, also called the light duration or day length, refers to the length of the light period as compared to the darkness within a day. The variation in photoperiod at different places is due to the differences in latitude, altitude, season and duration of the day. Due to longer duration of sunlight, trees grow faster in summer.

• Altitude

Increasing elevation causes a distribution of vegetation similar to that of increasing latitude. In general, ‘altitude mimics latitude’ and there occurs a close parallel between latitudinal and altitudinal zonation of climate and thus natural vegetation too. E.g. Mount Kenya in east Africa and Mount Chimborozo in Equador have their feet on the equator but their peaks are snow covered.

It was Alexander Von Humboldt who first recognised the relationship between vegetation and altitude.

The Forest Types of India:

Since India is a land of various climatic regions, varied kinds of natural vegetation have developed here. Having said that, rainfall is more important than temperature (except in the Himalayas) in determining the vegetation distribution in India. The seasonal rainfall distribution/the length of the dry season also affect the vegetation distribution in an important way.

In general, the following inter-relationship is observed in India:

Observe this broad relationship as highlighted in the following map:

High rainfall areas (>200cm) —> Evergreen forests grow in the high rainfall areas of the Western Ghats, North –eastern India and the Andaman and Nicobar Islands. These forests grow in areas where the monsoon period lasts for several months. There is no definite time for trees to shed their leaves, flowering and fruition. As such these forests appear green all the year round, hence the name evergreen.

Moderate Rainfall Areas (70-200cm) —>Deciduous forests are found in regions with a moderate amount of seasonal rainfall that lasts for only a few months. Most of the forests in which Teak trees grow are of this type. The deciduous trees shed their leaves during the winter and hot summer months.

Low Rainfall areas/ Semi-arid areas (<70cm) —> Thorn forests are found in the semi-arid regions of India. The trees, which are sparsely distributed, are surrounded by open grassy areas.

Apart from these, mangroves forests grow along the coast, especially in the river deltas. These plants are uniquely adapted to be able to grow in a mix of saline and freshwater (will be taken up in detail in the following sections.)

Natural Vegetation Types of India

1.Tropical Evergreen Forests

‘Evergreen’ because there is no definite time for trees to shed their leaves, flowering and fruition. As such these forests appear green all the year round.

The common animals found in these forests are elephants, monkey, lemur and deer. The one-horned rhinoceros are found in the jungles of Assam and West Bengal. Besides these animals, plenty of birds, bats, sloth, scorpions and snails are also found in these jungles.

Tropical Wet Evergreen Vegetation

• Distribution: These forests are found on the western slope of the Western Ghats, upper Assam through Cachar and the Andaman and Nicobar Islands.
• Climatic Conditions: They are found in warm and humid areas with an annual precipitation of over 250 cm and a short dry season. The mean annual temperature here is above 22°C.
• Characteristic Features:
• Tropical evergreen forests are well stratified, with layers closer to the ground covered with shrubs and creepers, followed by short structured trees, further followed by tall variety of trees.
• In these forests, trees reach great heights up to 60 m or above.
• Bounded by semi-evergreen forests on drier margins.
• Very rich biodiversity.
• Timber produced in these forests is fine-grained and durable.

• Important Species found in these forests: Rosewood, Mahogony, Aini, Ebony, etc. Important species in Kerala are Mesa, White cedar, Jamun, Canes etc. Common species found in Assam forests are Gurjan, Jamun, Agar, Bamboo etc.

Tropical Semi-Evergreen Vegetation

• Distribution: These forests occur in areas adjoining tropical wet evergreen, and form a transition between evergreen and moist deciduous forests. These forests occur on the western coast, in Assam, on the lower slopes of the eastern Himalayas and in the Andamans in the areas where precipitation and atmospheric humidity is slightly less than that in tropical evergreen vegetation area.
• Characteristic Features:
• Such forests have a mixture of evergreen and moist deciduous trees. The undergrowing climbers provide an evergreen character to these forests.
• The climbers are heavy, bamboos are less prevalent and epiphytes are abundant. [Epiphytes – The plants which depend on other plants for mechanical support (and not for nutrients). e.g. lichens, mosses, orchids etc.]
• The forest is dominated by a variety of large trees with a tendency to gregariousness (i.e. growing in groups that are close together)
• Plant Adaptations in these areas:
• Buttresses – Many large trees have huge ridges called buttresses near the base that can rise 30 feet high before blending into the trunk. Buttress roots provide extra stability and increase the surface area of a tree so that it can ‘breathe in’ more carbon dioxide and ‘breathe out’ more oxygen. Typically, they are found in nutrient-poor rainforest soils and do not penetrate to deeper layers.

Big trees with buttress roots in tropical evergreen forest, India, Andaman Islands, Havelock Island. 

• The bark is thicker and rougher, and the canopy is less dense than that in the previous type. Also, the canopies are not continuous and species richness is lower

• Main species are white cedar, hollock and kail. Important Species in Kerala are Aini, Laurel, Rosewood, thorny bamboo, etc. Important species of northeastern India are White Cedar, Indian Chestnut, Champa and Mango.

Tropical Dry Evergreen Vegetation

• Distribution: This type is confined to the Tamil Nadu coast and the areas which receive rainfall of about 100cm mostly from the north-east monsoon/winter monsoon (October-December).
• The growth of evergreen forests in areas of such low rainfall arouses great botanical interest. This vegetation may be due to the seasonal distribution of rainfall (winter rainfall).
• Characteristic Features of this vegetation:
• Short height trees (<12m)
• A closed but low canopy of grasses and shrubs.
• No canopy layer differentiation.
• Bamboos are rare /absent.

• Important Species found in these forests: Neem, Jamun, Tamarind, Machkund, Khirni, Kokko, Ritha, Gamari Canes.
• Most of the land under these forests has been cleared for agriculture or casuarinas plantations (Eucalyptus tree plantations)

2. Tropical Deciduous Vegetation

Also called the monsoon forests, these are the most widespread forests in India. The term ‘Deciduous’ refers to the ability of some plants to lose their leaves annually. They are spread over regions which receive rainfall between 70 and 200 cm.

In these forests, the common animals found are lion, tiger, pig, deer and elephant. A huge variety of birds, lizards, snakes, and tortoises are also found here. [Currently, India is the only country on Earth confirmed to have both lions and tigers in its wilderness.]

On the basis of the availability of water, these forests are further divided into:

Tropical Moist Deciduous Vegetation

• • Climatic Conditions: It thrives in areas having of moderate rainfall of 150-200 cm with a dry season of 4 to 6 months, a mean annual temperature of 26°C to 27°C and an average relative humidity of 60-80%. On the wetter margins, it has a transition to the tropical Semi-Evergreen Vegetation, while on the drier margins to the Tropical Dry Deciduous.
  • Distribution: It is found on the eastern slopes of the Western Ghats, eastern coastal plains, eastern plateaus, Himalayan foothills and in some parts of the Satluj-Ganga plains.
  • Characteristic Features:
    1. The trees shed their leaves during the dry season.
    2. These forests are usually 2 to 3 layered.
    3. Dense undergrowth

• Important Species: The common trees are Sal, Teak, Sandalwood, Ajun, Ebony, Shisham, Hurra, Mahua, Amla, Semul, Mulberry and Kusum.

Tropical Dry Deciduous Vegetation

• Climatic Conditions: The dry deciduous trees grow in areas where rainfall is less than 150cm and the dry period is relatively long. On the wetter margins, it has a transition to the moist deciduous, while on the drier margins to thorn forests.
• Distribution: It is found in Eastern Rajasthan, Kathiawar, rain-shadow areas of the Deccan plateau, central India and Punjab.
• Characteristic Features:
• These forests consist of trees less than 25m high, with a light canopy consisting of deciduous trees. The undergrowth is shrubby and grassy.
• As the hot dry season begins (March-May), the trees shed their leaves completely and the forest appears like a vast grassland with naked trees all around.
• In the higher rainfall regions of the Peninsular plateau and the northern Indian plain, these forests have a parkland landscape i.e. trees are more stunted and widely spaced and are interspersed with patches of grass.
• In the western and southern part of Rajasthan, vegetation cover is very scanty due to low rainfall and overgrazing.

• Important Species: Common plants are Teak, Sal, Laurel, Palas, Khair, Tendu, Amaltas, Bel, Axlewood etc.

3. Tropical Thorny Vegetation

• Climatic Conditions: In areas with 50-70cm of rainfall
• Distribution: It is found in south-western Punjab, western Haryana, western Uttar Pradesh, central and eastern Rajasthan, western Madhya Pradesh, Kachchhand, neighbouring parts of Saurashtra, leeward areas of Sahyadris.
• Characteristic Features:
• Plant life is highly specialized to adapt to the coarse and dry conditions in this area, with long roots, small leaves, stems that store water, and prickly spines that discourage animals from touching or eating them.
• The natural vegetation consists of open stunted (trees with 6-9m height) forest breaking down into xerophytic bush and western Rajasthan grading into deserts.
• In these forests, plants remain leafless for the most part of the year and give an expression of scrub vegetation.
• Plant adaptations:
• These xerophytic plants combat drought with certain devices of water preservation like partial or complete replacement of leaves by thorns, waxy leaves, water storing cells, hair on the stalk etc.
• Tussocky grass grows up to a height of 2 m as the undergrowth.
• Trees are scattered and have long roots penetrating deep into the soil in order to get moisture.
• The stems are succulent to conserve water.
• Leaves are mostly thick and small to minimize evaporation.

• Important Species: Common species are Babul, Acacia, Kokko, Khair, Khajuri, Ber, Neem, Khejri, Palas, etc.
• In these forests, the common animals are rats, mice, rabbits, fox, wolf, tiger, lion, wild ass, horses and camels.