Natural vegetation and biomes

The first principle

Plants grow where they get enough heat, water and nutrients for their way of life, so climate draws the broad map of vegetation and soil and relief fill in the detail. A biome is the large community of plants and animals that matches one climate, such as tropical rain forest, savanna or tundra. Because temperature falls with both latitude and height, and rain depends on winds and mountains, the same logic that sorts biomes from the equator to the poles also sorts belts of vegetation from the foot of a mountain to its summit.

The core

What decides natural vegetation

• Temperature sets the length of the growing season; most plants grow little below about 6°C, so the number of warm months decides whether forest, scrub or moss can survive.
• Rainfall decides how dense the cover is, and its season decides the type: rain all year gives evergreen forest, a long dry season gives deciduous forest that sheds leaves to save water, and very little rain gives thorn scrub with small leaves and deep roots.
• Soil, relief and drainage modify the climatic picture: waterlogged deltas carry mangroves, thin lateritic soils carry scrub, and slopes facing the sun are warmer and drier than shaded ones.
• Altitude cools air by about 6.5°C per kilometre, so mountains compress the whole sequence from tropical to polar vegetation into a few kilometres of height.

World biomes

• Tropical rain forest (Amazon, Congo, South East Asia): over 200 cm of rain and high heat throughout the year, many layered canopy, the richest biodiversity on land, yet poor soils because nutrients are held in living plants.
• Savanna (East Africa, the Llanos, northern Australia): a long dry season, tall grasses with scattered trees, kept open by fire and grazing.
• Hot desert (Sahara, Thar): under 25 cm of rain, with succulents and thorny plants.
• Mediterranean: winter rain and dry summers give hard leaved evergreen shrubs and trees such as cork oak and olive.
• Temperate grassland (steppe, prairie, pampas): moderate rain and cold winters; deep black soils have made them granaries.
• Temperate deciduous forest (Western Europe, eastern United States): oak, beech and maple that shed leaves in winter.
• Taiga (Siberia, Canada): long cold winters; needle leaved conifers such as spruce and fir that shed snow and keep leaves to photosynthesise in the short summer.
• Tundra (Arctic fringe): mean temperature of the warmest month below 10°C; mosses, lichens, sedges and dwarf shrubs on permafrost.
• Mountain vegetation repeats these belts with height.

Dimensions

Why India's natural vegetation is so diverse

India spans about 29° of latitude and about 8,800 m of relief, and its rain is brought by the monsoon, which falls unevenly across the country. Together these produce nearly every forest type found in the tropics and the temperate world.

• Rainfall ranges from over 1,000 cm at Mawsynram to under 20 cm in western Rajasthan, which gives a sequence from evergreen forest to thorn scrub.
• Relief creates rain shadows, such as the dry interior of Karnataka behind the Western Ghats, and the Himalaya packs tropical, temperate and alpine belts into one slope.
• Temperature and latitude separate the frost free south from the cooler north and the hills.
• Soils differ, from alluvium in the plains to laterite, black soil, desert sand and saline coastal soils.
• Biogeographic history brings together Indo Malayan species in the north east and Western Ghats, Palaearctic species in the Himalaya and African species in the arid west.
• Human use, through clearing, grazing, fire and shifting cultivation, has turned many moist forests into dry ones and scrub.

Forest types of India

The classification by H G Champion and S K Seth (1968) groups India's forests largely by rainfall and temperature.

In practice

Wildlife sanctuaries in India's rain forest regions and why they matter

India's tropical rain forests lie in three regions: the Western Ghats, the north east and the Andaman and Nicobar Islands. Their protected areas include Silent Valley National Park (Kerala), Periyar Tiger Reserve and the Anamalai hills, Namdapha National Park in Arunachal Pradesh, Nameri and Dibru Saikhowa in Assam, and the protected areas of the Andaman and Nicobar group.

• Biodiversity hotspots. Three of the four global hotspots in India (Western Ghats and Sri Lanka, Indo Burma, Sundaland covering the Nicobar Islands) fall in these rain forest regions; the fourth is the Himalaya.
• Endemic and threatened species. The lion tailed macaque (Macaca silenus) lives only in the Western Ghats rain forest, and Silent Valley was saved from a hydro project in the early 1980s partly to protect it. The great hornbill (Buceros bicornis) disperses large seeds; Namdapha holds four big cats, including the snow leopard and clouded leopard, and the hoolock gibbon.
• Watersheds. The Western Ghats forests feed the Godavari, Krishna, Kaveri and many west flowing rivers, so they protect water for much of peninsular India.
• Carbon and climate. Dense evergreen forests store large amounts of carbon per hectare and keep local climate humid.
• Livelihoods and culture. Communities such as the Kani of Kerala and the Lisu near Namdapha depend on forest produce; the Forest Rights Act, 2006 (Ministry of Tribal Affairs) recognises their rights.
• Ecotourism and research. Sanctuaries such as Periyar earn income that can be shared with local people through eco development committees.

Threats. Plantations, hydropower, roads, mining and fragmentation have broken up habitats; the Madhav Gadgil panel (2011) recommended declaring much of the Western Ghats ecologically sensitive, and the Kasturirangan committee (2013) proposed a narrower area of about 37 per cent.

Data

Laws and schemes

• Wild Life (Protection) Act, 1972 (Ministry of Environment, Forest and Climate Change): provides for sanctuaries, national parks and conservation and community reserves.
• Green India Mission (2014), under the National Action Plan on Climate Change: aims to increase and improve forest cover.

Issues and way forward

Is the tundra ecologically fragile but economically important?

• Fragile. The growing season lasts only about two months, food chains are short, and plants grow so slowly that a vehicle track or a lichen field grazed bare can take decades to recover. Permafrost, ground frozen for at least two years, holds the surface together; when it thaws the land slumps, lakes drain, and roads, pipelines and buildings crack, as the diesel spill from a failed tank at Norilsk in 2020 showed. The Arctic is warming about three times faster than the world as a whole, according to the Arctic Monitoring and Assessment Programme (2021).
• Important. The Arctic holds large oil and gas reserves, such as Prudhoe Bay in Alaska and the Yamal peninsula in Russia, and minerals such as nickel and palladium at Norilsk. Melting sea ice is opening the Northern Sea Route, which shortens the sea distance between Europe and East Asia by about a third compared with the Suez route. Reindeer herding by the Sami and Nenets, and fishing, sustain indigenous peoples.
• Global significance. Permafrost holds about twice as much carbon as the atmosphere, so its thaw releases carbon dioxide and methane that speed warming everywhere.
• Balance. The economic value is real, but every use presses on the fragility, so development needs strict environmental review, as the Arctic Council's assessments urge, and the rights of indigenous peoples.

Indian forests. Shifting cultivation, invasive species such as Lantana camara, forest fires and diversion for projects degrade forests; recognising community forest rights and restoring native species are better than monoculture plantations.

Common confusions

• Biome and ecosystem. A biome is a large regional community defined by climate; an ecosystem can be any size, from a pond to a forest.
• Forest cover and recorded forest area. Forest cover is land with over 10 per cent canopy seen by satellite, whatever its ownership; recorded forest area is land legally notified as forest.
• Tundra and taiga. Tundra is treeless because summers are too short and cold; taiga, to its south, has coniferous forest.
• Sanctuary and national park. Both are under the Wild Life (Protection) Act; a national park allows no rights inside, while a sanctuary may permit some.

For the exam

• Keyword bank: biome, climax vegetation, Champion and Seth, tropical evergreen, moist deciduous, thorn forest, montane forest, mangroves, altitudinal zonation, endemism, hotspot, lion tailed macaque, permafrost, Northern Sea Route, carbon store.
• Previous year questions: Practise the previous year questions on this topic →
• Use in an answer:
  • Introduction (data): Forests cover about 21.8 per cent of India's area, according to the India State of Forest Report 2023, yet within that cover lie almost every tropical and temperate forest type.
  • Introduction (judgement, quote or report): The Arctic Monitoring and Assessment Programme finds the Arctic warming about three times faster than the global average, which makes the tundra both a resource frontier and a climate warning.
  • Conclusion: India's rain forest sanctuaries are not islands of wildlife alone but the water towers, carbon stores and homes of forest peoples, and their protection must be built with local communities.
  • Conclusion: The tundra's wealth can be used only if its fragility is respected, because what thaws there affects climate everywhere.