Mains Paper II · 4 Environment & Ecology · 4.1 Ecology and ecosystems
4.1.7 Terrestrial biomes: ecology and adaptations
A biome is the largest recognisable assemblage of plants and animals on Earth, shaped mainly by temperature and rainfall, and its species show adaptations to those conditions.
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Core facts
- Biome: the largest recognisable assemblage of plants and animals, whose distribution is controlled mainly by climate, chiefly temperature and precipitation.
- Major terrestrial biomes:
- tropical rain forest
- tropical deciduous (monsoon) forest
- savanna
- desert
- temperate grassland
- temperate deciduous forest
- Mediterranean scrub
- taiga (boreal coniferous forest)
- tundra
- Tropical rain forest: hot and wet all year, very high diversity, multi-layered canopy.
- Savanna: tropical grassland with scattered trees; fire and grazing maintain it.
- Desert: very low rainfall (usually below about 25 cm a year); xerophytes and water-saving animals.
- Taiga: coniferous forest of the cold north, between temperate forest and tundra.
- Tundra: treeless; permafrost below the surface; lichens and mosses; reindeer (caribou).
- India's forests are classified by Champion and Seth (1968) into 16 type groups.
- Tropical dry deciduous and tropical moist deciduous forests are the most widespread forest type groups in India.
Explained
Main biomes at a glance
| Biome | Climate | Typical life |
|---|---|---|
| Tropical rain forest | Hot; heavy rain all year | Tall evergreen trees, lianas, epiphytes; Amazon, Congo, South-East Asia; in India, Western Ghats and the north-east |
| Tropical deciduous | Hot; seasonal (monsoon) rain | Teak, sal; trees shed leaves in the dry season |
| Savanna | Hot; long dry season | Grasses and scattered trees; large herds of grazers in Africa |
| Desert | Very dry; extreme day–night range | Cacti, thorny shrubs; kangaroo rat, camel |
| Temperate grassland | Cold winters, warm summers, moderate rain | Grasses; deep fertile soils; prairies, pampas, steppes, veld, downs |
| Temperate deciduous | Four seasons | Oak, maple, beech |
| Taiga | Long cold winter, short summer | Spruce, fir, pine; moose |
| Tundra | Very cold; short summer | Lichens, mosses, dwarf shrubs; reindeer, Arctic fox |
Temperate grasslands by region
| Name | Region |
|---|---|
| Prairies | North America |
| Pampas | South America (Argentina) |
| Steppes | Eurasia |
| Veld | South Africa |
| Downs | Australia |
Adaptations to desert life
- Plants (xerophytes): thick cuticle; sunken stomata; leaves reduced to spines; photosynthesis in a flattened stem (Opuntia); deep or wide roots; CAM photosynthesis, in which stomata open at night.
- Animals: the kangaroo rat gets water from oxidising fat and passes very concentrated urine; many animals are active at night; camels tolerate water loss.
Adaptations to cold
- Allen's rule: mammals from colder climates have shorter ears and limbs, which cut heat loss.
- Bergmann's rule: within a related group, animals in colder climates tend to have larger bodies. A larger body has less surface area per unit volume, so it loses heat more slowly.
- Thick fur, blubber (seals), hibernation and migration.
Deeper
Why the rain forest is rich but its soil is poor
- Warm, wet conditions speed decomposition. Nutrients are taken up by plants almost as soon as they are released, so most nutrients sit in the vegetation, not in the soil.
- Heavy rain leaches the soil, leaving it poor (lateritic in many places).
- So when the forest is cleared, crops fail within a few years and the land degrades. Shifting cultivation works only with long fallows.
Indian forest types (Champion and Seth)
| Type group | Rainfall (approx.) | Where in India |
|---|---|---|
| Tropical wet evergreen | Above 250 cm | Western Ghats, north-east, Andaman and Nicobar |
| Tropical moist deciduous | 100–200 cm | Eastern slopes of Western Ghats, Odisha, Jharkhand, Terai |
| Tropical dry deciduous | 70–100 cm | Peninsular plateau, much of Andhra Pradesh |
| Tropical thorn | Below 70 cm | Rajasthan, Gujarat, dry rain-shadow parts of the Deccan |
| Montane temperate and alpine | Varies with altitude | Himalaya, Nilgiris |
- Whittaker's biome diagram places biomes on two axes: mean annual temperature and mean annual precipitation. Fire, soil and grazing can shift the boundary (for example, between savanna and forest).
- Altitude mimics latitude. Climbing a Himalayan slope passes through tropical, temperate, coniferous and alpine zones, much like travelling from the equator to the Arctic.
- Tundra and taiga hold large stores of soil carbon in permafrost. Thawing releases carbon dioxide and methane, which adds to warming (see ENV-BC-02).
AP angle
- Most of Andhra Pradesh's forest is tropical dry deciduous, with tropical thorn forest in the drier Rayalaseema districts.
- The Nallamala and Seshachalam hills of the Eastern Ghats are the main forest tracts. Nagarjunasagar–Srisailam Tiger Reserve, in the Nallamala, is India's largest tiger reserve by area.
- Red sanders (Pterocarpus santalinus) is endemic to the southern Eastern Ghats, mainly in AP's Seshachalam and nearby hills. It is a dry deciduous species, now listed as endangered, and smuggling is a major problem.
- Seshachalam Biosphere Reserve (notified 2010) protects this dry deciduous landscape.
Common traps
- ✗ "Biome distribution is controlled mainly by soil." ✓ It is controlled mainly by climate (temperature and rainfall).
- ✗ "Rain forest soils are very fertile." ✓ They are generally poor; nutrients are held in the vegetation.
- ✗ "Pampas are in Australia." ✓ Pampas are in South America. Australia has the Downs; South Africa the Veld.
- ✗ "Allen's rule says cold-climate animals are larger." ✓ That is Bergmann's rule. Allen's rule is about shorter limbs and ears.
- ✗ "Tropical evergreen forest is India's most widespread type." ✓ Tropical dry and moist deciduous forests are the most widespread.
Quick revision
- Biome: largest assemblage; controlled by temperature and rainfall.
- Rain forest: hot, wet, diverse, poor soil.
- Savanna: grassland with scattered trees; fire maintains it.
- Taiga = boreal conifers; tundra = treeless, permafrost.
- Prairies (N. America), pampas (S. America), steppes (Eurasia), veld (S. Africa), downs (Australia).
- Allen's rule: short limbs in cold; Bergmann's rule: larger body in cold.
- Desert plants: CAM, sunken stomata, spines; kangaroo rat makes metabolic water.
- Champion and Seth (1968): 16 forest type groups.
- Deciduous forests most widespread in India.
- Red sanders: endemic to AP's southern Eastern Ghats.
Go deeper: Mains writing (beyond what APPSC Group 2 usually asks)
Mains writing Mains writing
- Frame: biomes are set by climate, so climate change is moving biome boundaries. Species that cannot move fast enough face loss.
- Analysis points:
- Rain forest loss removes a large carbon sink and much of global biodiversity, and the poor soils make recovery slow.
- Grasslands are undervalued: in India, many are classed as "wasteland" and planted with trees, which harms grassland species such as the great Indian bustard.
- Deserts are spreading where land is degraded (desertification), not only where climate is dry.
- Mountain biomes are shifting upward; alpine species run out of space at the top.
- Way forward:
- protect each biome type, including grasslands and scrub
- restore degraded land with native species suited to the biome
- climate-resilient corridors along altitude and latitude gradients
- Example: India's tropical dry deciduous forests (central India, Deccan) hold most of the country's tigers and much of its tribal population, so their protection links conservation with livelihoods.
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