Forest types and world biomes
World biomes and forest types: how climate shapes vegetation, tropical to boreal, Champion and Seth's 16 Indian type groups, and India's forest cover.
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Fly from the Western Ghats to the Thar Desert, or from the Assam plains to the Himalayan tree line, and the vegetation changes dramatically. Tall evergreen forest gives way to teak and sal, then to thorny scrub, or to oak, deodar, fir, birch and finally alpine meadows. These patterns are not random. On a global scale, climate, mainly temperature and rainfall and its seasonality, decides what kind of vegetation can grow. Within a climate, soil, topography, fire and human use shape the details.
A biome is a large region with a characteristic climate and vegetation structure, such as tropical rainforest, savanna or boreal forest. A forest type is a finer unit: a forest with a particular composition and structure in a particular region. Foresters use type classifications to plan management, silviculture and conservation.
The world's major biomes
Forests cover about 4.06 billion hectares, roughly 31% of the world's land area (FAO, 2020). The largest share is tropical (45%), followed by boreal (27%), temperate (16%) and subtropical (11%).
Tropical rainforest
Tropical rainforest grows where it is warm all year and wet, with more than about 200–250 cm of rain spread through the year. It has the greatest species diversity of any terrestrial biome. Its features are a tall, multi-layered canopy with emergent trees, buttresses, lianas and epiphytes. Nutrients are held mostly in the living biomass, and the soils are often poor. Major areas are the Amazon, the Congo basin and Southeast Asia. In India it occurs in the Western Ghats, the north-east and the Andamans.
Tropical dry, seasonal and monsoon forests
These grow where rainfall is moderate and falls in a marked wet season, followed by a long dry season. Many trees are deciduous, shedding their leaves to survive the dry months. They include India's teak and sal forests, which are the country's most extensive forest types.
Savanna
Savanna is grassland with scattered trees, found in hot regions with a long dry season. Fire and grazing animals maintain its open structure. It covers large areas of Africa, Australia and South America.
Deserts
Deserts get less than about 25 cm of rain a year. Their plants are xerophytes with deep or shallow spreading roots, succulence, small or no leaves, and thick cuticles. Hot deserts include the Sahara and Thar; cold deserts include Ladakh and Central Asia.
Temperate grassland
Temperate grassland includes the prairies, steppes and pampas. It has rich, deep soils (Mollisols), and today much of it is cropland.
Temperate deciduous and temperate rainforest
Temperate deciduous forest grows in moderate climates with cold winters and adequate rain all year. Typical trees are oak, maple, beech and, in the Himalaya, broadleaf species. Very wet temperate coasts have temperate rainforest, with giant conifers such as redwood and Douglas fir.
Boreal forest (taiga)
Boreal forest is the world's largest land biome, stretching across Canada, Scandinavia and Russia. Long cold winters and short summers favour conifers: spruce, fir, pine and larch. Cold, acid soils (Spodosols) store very large amounts of carbon.
Tundra
Beyond the tree line, the growing season is too short and cold for trees. Tundra has dwarf shrubs, mosses, lichens and grasses over permafrost. Alpine tundra occurs above the tree line on high mountains.
Indian forest types: Champion and Seth
India's standard classification is Champion and Seth (1968), A Revised Survey of the Forest Types of India. It is based on climate, mainly rainfall and temperature, together with physiognomy and composition. It recognises 16 type groups within five major groups, divided into more than 200 individual types.
| Major group | Type groups |
|---|---|
| Tropical | 1. Wet evergreen; 2. Semi-evergreen; 3. Moist deciduous; 4. Littoral and swamp; 5. Dry deciduous; 6. Thorn; 7. Dry evergreen |
| Subtropical | 8. Broadleaved hill; 9. Pine; 10. Dry evergreen |
| Montane temperate | 11. Wet temperate; 12. Himalayan moist temperate; 13. Himalayan dry temperate |
| Sub-alpine | 14. Sub-alpine |
| Alpine scrub | 15. Moist alpine scrub; 16. Dry alpine scrub |
Some examples:
- Tropical moist deciduous forests are dominated by sal in the north and east and teak in the peninsula.
- Tropical dry deciduous forests contain teak, Terminalia, Anogeissus and Boswellia.
- Tropical thorn forests in Rajasthan and Gujarat contain Prosopis, Acacia and Capparis.
- Littoral and swamp forests include the mangroves of the Sundarbans, the largest mangrove forest in the world.
- Subtropical pine forests are dominated by chir pine (Pinus roxburghii).
- Himalayan moist temperate forests contain oaks, deodar, blue pine, fir and spruce.
Tropical moist deciduous and tropical dry deciduous forests together cover the largest share of India's forest area.
Placing a site in its type group
A district in central India receives about 120 cm of rain, almost all of it from June to September, with a hot dry season, and its forests are dominated by teak. That combination of moderate monsoon rainfall, a long dry season and deciduous teak fits tropical moist deciduous forest, near its drier limit. If annual rainfall fell to about 70 cm and Anogeissus and thorny species became common, the site would move toward tropical dry deciduous, and below about 50 cm toward tropical thorn forest. Rainfall thresholds are only guides; soil, fire history and grazing also matter.
India's forest cover
The Forest Survey of India assesses forest cover every two years from satellite imagery. In its India State of Forest Report 2023:
- Forest cover was about 7.15 lakh km2, roughly 21.8% of the geographical area.
- Forest and tree cover together were about 25% of the geographical area.
Forest cover is classified by canopy density as very dense (70% or more), moderately dense (40–70%) and open forest (10–40%). Scrub has less than 10% canopy. The National Forest Policy of 1988 set a goal of one-third of the land area under forest or tree cover, and two-thirds in the hills.
Key points
- Climate, mainly temperature and rainfall seasonality, determines biomes; soil, fire and people shape the details.
- The major forest biomes are tropical rainforest, tropical seasonal forest, temperate deciduous, temperate rainforest and boreal forest. Non-forest biomes include savanna, grassland, desert and tundra.
- Forests cover about 31% of the world's land area, 45% of them tropical.
- Champion and Seth (1968) classify India's forests into 16 type groups within five major groups (tropical, subtropical, montane temperate, sub-alpine and alpine).
- Tropical moist and dry deciduous forests are the most extensive in India.
- FSI density classes are very dense (70% or more), moderately dense (40–70%) and open (10–40%).
What the exams ask
- Describe the main world biomes and their climates.
- List Champion and Seth's 16 forest type groups.
- Give characteristic species of named Indian forest types.
- State India's forest cover and the FSI density classes.
- Explain the climatic basis of forest classification.
Described in general terms: the kind of examination, not a past paper. Laisha never reproduces exam questions.
Questions people ask
Why are tropical rainforest soils poor if the forest is so lush?
High rainfall and temperatures weather the soil deeply and leach nutrients. Most nutrients are held in the living vegetation and the thin litter layer, and they are recycled quickly by decomposers and mycorrhizae. When the forest is cleared, nutrients are lost quickly, and crop yields fall after a few seasons.
What is the difference between forest cover and recorded forest area?
Recorded forest area is land legally designated as forest in government records, whether or not it carries trees. Forest cover is land with more than 10% tree canopy and at least one hectare in size, mapped from satellites, regardless of ownership or legal status. The two overlap but differ considerably.
Are mangroves forests?
Yes. Mangroves are salt-tolerant trees and shrubs of tropical coasts and estuaries, classified under littoral and swamp forests. They protect coasts from storms and erosion, nurse fisheries, and store very large amounts of carbon in their soils.
Sources
- Champion, H. G. and Seth, S. K. A Revised Survey of the Forest Types of India. Manager of Publications, Government of India, New Delhi, 1968.
- FAO. Global Forest Resources Assessment 2020: Main Report. FAO, Rome, 2020.
- Forest Survey of India. India State of Forest Report 2023. FSI, Dehradun, 2024.
- Whittaker, R. H. Communities and Ecosystems, 2nd edition. Macmillan, 1975.
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