Natural regions I: rainforests, savannas, monsoon lands, taiga and tundra

Detail

1. The natural-region idea

• Natural region: a large area where climate, natural vegetation, animal life and human ways of life are broadly the same. A. J. Herbertson (British geographer) put forward this idea in 1905.
• Why it works:
• Climate (temperature and rainfall) decides which plants can grow.
• Plants decide which animals can live there.

• Plants, animals and climate together shape what people farm, herd, hunt or mine.

• Link to Koeppen: Koeppen's climate letters (A = tropical humid, B = dry, C = warm temperate, D = cold snow-forest, E = polar; small letters f = no dry season, m = monsoon, w = dry winter) can be read as landscapes. For example, Af = rainforest, Aw = savanna, Dfc = taiga and ET = tundra.

• Biome: a large natural zone with similar plants and animals, such as tropical rainforest, savanna or taiga.

Region	Koeppen	Latitude belt (approx.)	Vegetation	Typical economy
Equatorial rainforest	Af	0–10° N/S	Evergreen, layered hardwoods	Shifting cultivation, plantations
Tropical monsoon	Am (Aw in Asia)	10–25° N, mainly South and South-East Asia	Tropical deciduous forest	Wet rice, dense population
Savanna	Aw	5–20° N/S	Tall grass, scattered trees	Pastoralism, big game, ranching
Taiga	Dfc, Dwc	50–70° N	Conifers	Lumbering, pulp, fur
Tundra	ET	Beyond the tree line (about 65–75° N)	Mosses, lichens, dwarf shrubs	Herding, hunting, oil and gas

2. Equatorial (Af) rainforest

• Climate: hot and wet all year. Every month gets rain, and there is no real dry season.
• The sun is high all year → strong heating → air rises → convectional rain (rain from rising, heated air) falls almost daily in the afternoon.

• The difference between the hottest and coldest month (annual range of temperature) is very small, only about 2–3°C.

• Location: the Amazon basin (South America), the Congo basin (Africa), and South-East Asia (Indonesia, Malaysia, Borneo, Sumatra, New Guinea).

• Vegetation: dense, evergreen forest (trees do not shed all their leaves at one time). It grows in layers (storeys):
• Emergents: the tallest trees, which stick out above the rest.
• Canopy: a closed roof of crowns that blocks most sunlight.
• Understorey: young trees and shrubs.
• Forest floor: dark, with little growth.
• Typical hardwoods are mahogany, ebony and rosewood. Many tree species grow mixed together, so there are few pure stands. This makes commercial logging hard.

• Lianas (woody climbers) and epiphytes (plants that grow on other plants) are common.

• Soils are poor:

• Heavy rain → water moves down through the soil → nutrients are washed out (leaching) → a red, poor soil (laterite) is left.

• Most nutrients are stored in the living plants, not in the soil. Once the forest is cleared, fertility drops fast.

• People:

• Mbuti (Congo basin, DR Congo): hunter-gatherers.

• Yanomami (Amazon, on the Brazil–Venezuela border).

• Economy:

• Shifting cultivation: people clear a patch of forest, often by slash-and-burn, farm it for a few years until the soil is tired, then move on and let the forest grow back. Local names: milpa (Central America, Mexico), ladang (Malaysia, Indonesia), roca (Brazil), jhum (North-East India).
• Plantations: large estates that grow one cash crop, such as rubber and oil palm (Malaysia, Indonesia), or cocoa (West Africa).

3. The Amazon rainforest

• The largest tropical rainforest, about 5.5 million sq km.
• Spread: mostly in Brazil, and shared by nine countries and territories: Brazil, Peru, Colombia, Venezuela, Ecuador, Bolivia, Guyana, Suriname and French Guiana (an overseas territory of France).
• Threats:
• Forest is cleared for cattle ranching and soy farming, and fires are set to clear land.
• Tipping point: a point of no return, after which a system changes to a new state and cannot easily go back.

• How it could happen in the Amazon:

  • The forest makes much of its own rain by recycling moisture: trees release water vapour, which falls again as rain further west.
  • Clearing → less water vapour → longer dry seasons → more fires.
  • Past a certain threshold, parts of the forest may turn into degraded savanna.

• Diplomacy:

• The Amazon Cooperation Treaty was signed on 3 July 1978 by Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, Suriname and Venezuela. These eight countries formed the Amazon Cooperation Treaty Organization (ACTO) in 1995 to carry out the treaty [4]. French Guiana is not a member because it is part of France.
• COP30 (the 30th UN Climate Change Conference) was held at Belém, in Brazil's Pará state, in November 2025. It was the first COP held in the Amazon [5]. The conference closed with an agreement on 22 November 2025 [6].

4. The Congo Basin rainforest

• The second-largest tropical rainforest.
• Spread: DR Congo (the largest share), Republic of Congo, Cameroon, Gabon, Central African Republic and Equatorial Guinea. It is drained by the Congo river, which crosses the equator twice.
• Cuvette Centrale: a shallow, saucer-shaped low area in the middle of the basin.
• Peatland: wet land made of half-rotted plants. The plants do not fully rot because the ground is waterlogged, so the land stores carbon.
• The Cuvette Centrale is the largest tropical peatland complex in the world. It covers about 167,600 sq km (mapped in 2017) [2].
• It is about the size of the United Kingdom and lies across DR Congo and the Republic of Congo [3].
• It stores about 30.6 billion tonnes (petagrams) of carbon below ground. This raised the best estimate of the world's tropical peat carbon by about one-third (2017 estimate) [2]. That carbon equals about 15 years of US emissions [3].
• Peat began to form about 10,600 years ago, when central Africa became wetter at the start of the Holocene [2].

• Risk: draining, logging or drought would dry the peat → the peat would rot or burn → the stored carbon would be released as CO₂.

• South-East Asian rainforests: Borneo (Malaysia, Indonesia, Brunei) and Sumatra (Indonesia) lose forest to oil palm plantations. When peat swamps there are drained, peat fires cause haze across the region.

5. Tropical grasslands (Aw: savanna)

• Definition: grassland with scattered trees. It lies between the equatorial rainforests and the hot deserts, roughly 5–20° N and S.
• Climate (Aw): one wet season in summer and one dry season in winter.
• In summer the ITCZ (Inter Tropical Convergence Zone: the low-pressure belt where the trade winds of the two hemispheres meet) moves over the region and brings rain.

• In winter the ITCZ moves away, the dry trade winds blow, and there is drought.

• Vegetation: tall grass (elephant grass, up to about 3–4 m) and drought-resistant trees:

• Acacia: umbrella-shaped.
• Baobab: stores water in a thick trunk.

• Many trees are deciduous (they shed their leaves in the dry season).

• What keeps them open: dry-season fire and grazing by wild and domestic animals stop forests from taking over.

Savanna	Location	Key features
African savanna	East and Central Africa: Serengeti (Tanzania), Maasai Mara (Kenya)	Wildebeest migration; acacia and baobab; Maasai pastoral herders
Llanos	Venezuela and Colombia, in the Orinoco basin	Seasonal flooding; cattle ranching
Campos and Cerrado	Brazilian Highlands	Cerrado = woody savanna; now a soy frontier
Northern Australia	Northern Territory, Queensland	Cattle stations; fire-managed

• The great wildebeest migration:
• About 1.5 million wildebeest move around the Serengeti plains for about seven months of each year, looking for grass and water. They travel in a clockwise loop, following the rains [7].
• Together with zebras, gazelles and predators, they cover about 1,000 km [7].

• UNESCO lists the Serengeti as the site of the largest unaltered animal migration in the world [8].

• Uses: big-game tourism and national parks; pastoralism (keeping cattle, goats and camels on natural grazing land), often nomadic; and commercial ranching in the Llanos and Australia.

6. Tropical monsoon lands (Am; Aw in Asia)

• Location: India, Bangladesh, Myanmar, Thailand, Indo-China, the Philippines and northern Australia.
• Climate: a seasonal reversal of winds.
• Summer: land heats up → low pressure over land → moist winds blow in from the ocean → heavy rain from June to September in India.

• Winter: winds blow from the dry land → a long dry season.

• Vegetation: tropical deciduous forest, such as teak and sal, which sheds its leaves in the dry season to save water. Where rain is very heavy (for example the Western Ghats and Myanmar coast, Am), there is tropical evergreen forest.

• People and economy: wet rice farming that depends on the monsoon, along with jute and sugarcane. These lands have some of the densest rural populations in the world, such as the Ganga delta.

7. Taiga (boreal coniferous forest)

• Definition: the belt of coniferous forest (cone-bearing trees with needle leaves) at about 50–70° N. It is the world's largest land biome. It is found only in the Northern Hemisphere, because the Southern Hemisphere has almost no land at these latitudes.
• Extent: northern North America (Alaska, Canada), Scandinavia and Siberia. Of the closed boreal forest, 73% is in Russia, 22% in Canada and Alaska, and 5% in the Nordic countries [9].
• Climate (Dfc, Dwc):
• Dfc: long, very cold winters; short, cool summers; snow, and no dry season. Found in Canada and Scandinavia.
• Dwc: a dry winter under the Siberian High (a large cold high-pressure area over Siberia in winter). Found in eastern Siberia.

• The annual range of temperature is very large. Interior Siberia has one of the largest ranges on Earth.

• Vegetation: pine, spruce, fir and larch. Larch sheds its needles in winter. The trees are cone-shaped so snow slides off, and their needle leaves lose little water. Large areas have only one or a few species (pure stands), which makes logging easy.

• Economy: softwood lumbering (logs float down rivers in spring); pulp and paper; fur trapping (sable, mink). Population is sparse.
• Warming threats:
• Fire is the main natural disturbance in the taiga [10].
• Between 1981 and 1989, about 3 million hectares burned each year in the Soviet Union, almost all in the Russian taiga. During the 20th century, about 1 million hectares of Canadian taiga burned each year [10].
• How warming feeds fire: warmer, drier summers → drier fuel → more and larger fires, plus insect outbreaks such as bark beetles → the forest releases carbon instead of storing it.

8. Tundra (ET)

• Location: beyond the tree line (the limit beyond which trees cannot grow, roughly where the warmest month averages about 10°C). It covers northern Canada, Alaska, Greenland's coastal fringe, northern Scandinavia and northern Russia.
• Climate (ET): the warmest month is between 0°C and 10°C. There is a very short growing season and little precipitation.
• Permafrost: ground that stays frozen all year. In summer only the top layer thaws (the active layer). Water cannot drain through the frozen ground, so the land becomes bogs and shallow pools.
• Vegetation: mosses, lichens and dwarf shrubs (dwarf willow, birch). Reindeer moss is a lichen that reindeer eat.
• People:
• Inuit: Canada and Greenland. They hunt seals, whales and caribou.
• Sami: northern Norway, Sweden, Finland and Russia. They herd reindeer.
• Nenets: north-west Siberia, Yamal. Reindeer herders.

• Yakuts (Sakha): north-east Siberia.

• Economy today: oil and gas at Prudhoe Bay (Alaska, USA) and on the Yamal Peninsula (Russia, with Yamal LNG). As Arctic sea ice melts, the Northern Sea Route along Russia's Arctic coast is opening up (Section 11).

• Threat: permafrost thaw → buildings and pipelines sink and crack, and stored methane and CO₂ escape → more warming.

9. Other natural regions (sketch)

Region	Koeppen	Where	Way of life
Hot desert	BWh	Sahara, Arabia, Thar, Kalahari, Atacama	Oasis farming (dates), nomadic herding, mining (oil, phosphates)
Mediterranean	Cs	Mediterranean Sea lands, California, central Chile, SW Australia, Cape Town	Winter rain; citrus, grapes, olives (Section 7)
Temperate grassland	BSk/Dfa	Prairies, Steppes, Pampas, Veld, Downs	Wheat, ranching (Section 7)
China type	Cfa	South-east China, south Japan, south-east USA	Rice, tea, silk; dense population
British type	Cfb	NW Europe, British Columbia, New Zealand, south Chile	Mixed farming, dairying, fishing
Laurentian (cool east margin)	Dfa/Dfb	NE USA and SE Canada; NE China, Korea, north Japan	Cold winters; lumbering, fishing, maize and soybean

Prelims Hooks

• Herbertson (1905) put forward the idea of natural regions, not Koeppen. Koeppen classified climates.
• Rainforest size order: Amazon > Congo Basin. The largest tropical peatland is the Cuvette Centrale (DR Congo and Republic of Congo), about 167,600 sq km [2].
• ACTO has 8 members: Bolivia, Brazil, Colombia, Ecuador, Guyana, Peru, Suriname, Venezuela [4]. Trap: French Guiana is in the Amazon but is not a member, because it belongs to France.
• COP30 → Belém, Brazil (November 2025) [5].
• Savanna–country pairs: Llanos → Venezuela and Colombia (Orinoco); Campos and Cerrado → Brazil; Serengeti → Tanzania; Maasai Mara → Kenya.
• Shifting cultivation names: milpa (Mexico, Central America), ladang (Malaysia, Indonesia), roca (Brazil), jhum (NE India).
• Taiga is only in the Northern Hemisphere. Russia holds about 73% of the closed boreal forest [9].
• Larch is a conifer that is deciduous (it sheds its needles in winter). This is a common trap in "all conifers are evergreen" questions.
• People–region pairs: Mbuti → Congo; Yanomami → Amazon; Sami → Scandinavia (reindeer); Nenets → Yamal; Inuit → Canada and Greenland.
• Oil and gas fields: Prudhoe Bay → Alaska (USA); Yamal → Russia.

Mains Points

• Rainforest tipping point (GS-III):
• Cattle and soy clearing plus fire cut the Amazon's moisture recycling, which risks turning the forest into savanna.
• The response is regional cooperation through ACTO (1978 treaty) [4] and Amazon-centred climate diplomacy at COP30, Belém (2025) [5][6].

• Africa's parallel is the peat carbon of the Cuvette Centrale, about 30.6 billion tonnes [2].

• Poor soils under rich forest (GS-I):

• Leaching leaves rainforest soils poor, so cleared land loses fertility within a few years.

• This explains why farmers keep moving (shifting cultivation, as with jhum in North-East India) and why plantations need fertiliser.

• Savanna pressures (GS-I/III):

• Fire and grazing keep savannas open, but conversion is spreading. The Cerrado is now a soy frontier, and fences and settlement block migration routes.

• The Serengeti migration of about 1.5 million wildebeest shows the value of protecting large connected landscapes [7][8].

• High latitudes under warming (GS-I/III):

• Taiga fires (millions of hectares a year in Russia and Canada) [10] and permafrost thaw release stored carbon and damage infrastructure.
• Warming also opens the Arctic to oil and gas (Prudhoe Bay, Yamal) and to the Northern Sea Route. This brings economic gain but threatens the herding livelihoods of the Sami and Nenets.