Natural Vegetation and Major Biomes of the World

1.1 Why do biomes differ?

A biome is a large area with similar plants and climate. UC Berkeley groups biomes by their main plants and how those plants suit the place.

Forests alone cover about one-third of Earth’s land. They hold about 70% of the carbon in living things. Rain is the easiest clue to a biome. Look at the numbers below.

• Desert: under 300 mm a year.
• Grassland: about 500 to 950 mm.
• Tropical forest: over 2,000 mm.

1.2 Which biome is driest?

NASA calls deserts the driest of all biomes. A desert gets only a tenth of the rain a rainforest gets. Tundra gets only 150 to 250 mm a year, so it is much like a desert.

1.3 What is the common mistake?

Many people think the tundra is dry because it looks like a desert. It is dry in rainfall terms.

But NASA says it is usually a wet place. Cold air slows the loss of water, so water stays in bogs and ponds.

2.1 Where do tropical forests grow?

Tropical forests lie near the equator. UC Berkeley puts them between 23.5 degrees north and 23.5 degrees south. They have the greatest variety of species.

2.2 What is a rainforest like?

The tropical rainforest is hot and moist. It rains all year.

NASA gives an average daily temperature of 20 to 25 C. Giant trees in the top layer, the canopy, reach 75 m or more. They block most sunlight from the ground.

2.3 What is a monsoon forest?

Some tropical forests have a dry season. UC Berkeley calls these moist or dry deciduous forests, or monsoon forests. The longer the dry season, the more trees shed leaves. In the driest type, all trees are deciduous.

2.4 Are all rainforests tropical?

No. NASA says there are two types, tropical and temperate. Tropical rainforests lie closer to the equator. Temperate rainforests lie farther north, near coasts.

2.5 Where is an Indian example?

The Western Ghats. IUCN says their forests are among the best examples of non-equatorial tropical evergreen forests anywhere.

The high forests also help shape the Indian monsoon. So here the forest and the rain are linked in both directions.

3.1 Where are they found?

NASA says they lie in the mid-latitudes, between the polar regions and the tropics. UC Berkeley names eastern North America, north-eastern Asia, and western and central Europe.

Sources: NASA Science; UC Museum of Paleontology.

3.2 What do the trees do each year?

These forests have four seasons. In the fall, trees change colour and then lose their leaves. The leaves are broad. They are lost every year, after the fall colours, not in summer.

3.3 Why do the trees drop their leaves?

Winter is cold, so the trees go into a rest period called dormancy. NASA gives the average yearly temperature as about 10 C. Rain of 750 to 1,500 mm is spread fairly evenly through the year.

So the stress here is cold, not drought. That is the key difference from a monsoon forest.

3.4 Which trees grow here?

NASA lists broadleaf trees such as oak, maple, beech, hickory and chestnut.

4.1 Where is the boreal forest?

NASA says it lies between the tundra to the north and the deciduous forest to the south. UC Berkeley calls boreal forests, or taiga, the largest land biome. They lie between 50 and 60 degrees north.

4.2 What are the trees like?

Conifers are evergreen. They bear needles all year. The canopy lets little light through, so the understory is limited.

NASA says needles help conifers survive where it is very cold or dry.

4.3 How much rain do they get?

NASA gives 300 to 900 mm a year. Some temperate coniferous forests get up to 2,000 mm. In lower latitudes, rain is spread more evenly through the year.

In the northern boreal forest, winters are long, cold and dry. Summers are short, moderately warm and moist.

4.4 Is there a Himalayan link?

Yes. In the Great Himalayan National Park, forest changes with height. Mixed forest of horse chestnut, evergreen oak, spruce and deodar gives way to kharsu oak, spruce and fir in the upper temperate zone.

5.1 What is a grassland?

UC Berkeley says grasslands are dominated by grasses, not large shrubs or trees. There are two main kinds: tropical grasslands, called savannas, and temperate grasslands.

5.2 What are the temperate names?

The same biome has different local names. See the chart.

The Prairie of North America and the Steppe of Central Eurasia are both temperate grassland. So the Prairie matches the Steppe.

5.3 What is a savanna?

A savanna is grassland with scattered trees. Climate is the main factor.

Rain falls in six or eight months, then a long drought brings fires. Fires and large grazing animals kill seedlings. That keeps trees and shrubs low. Savannas cover almost half of Africa.

The Serengeti plains and Kenya’s Laikipia plateau are drier savannas.

5.4 What if the rain came all year?

UC Berkeley says many savanna areas would then turn into tropical forest. So the long dry spell is not a side detail. It is what holds the grass in place.

5.5 Are there other kinds of savanna?

• Climatic: made by the rain pattern.
• Edaphic: caused by soil, such as shallow hill soil or waterlogged clay.
• Derived: made by people who clear forest for farming.

5.6 What about India?

UC Berkeley lists India among the places with large savanna areas. A good Indian grassland is Kaziranga in Assam. IUCN says wet alluvial grasslands cover nearly two-thirds of the park.

Annual floods and burning keep them going. They support the one-horned rhinoceros and the wild water buffalo. Note that this is a flood grassland, not a dry savanna.

6.1 What is Mediterranean scrub?

It is the most extensive scrubland. The plants are shrubs. They suit a Mediterranean climate, which has a severe summer drought. They are also adapted to repeated fire.

6.2 What are its names?

The same scrub has a new name on each continent.

• Chaparral: California.
• Maquis: the Mediterranean.
• Mallee: Australia.
• Matorral: Chile.
• Fynbos: south-western South Africa.

6.3 Where does it grow?

NASA places shrublands on west coasts between 30 and 40 degrees north and south. They get 200 to 1,000 mm of rain a year. A CAPF question on this is on the CAPF (ACs) 2020 paper.

7.1 What makes a desert?

Little rain is the key. NASA says most deserts get under 300 mm a year. A rainforest gets over 2,000 mm. So a desert gets about 10 percent of a rainforest’s rain.

7.2 Why are desert nights cold?

The air is so dry that heat escapes fast after dark. NASA gives a daytime average of 38 C. In some deserts the night falls to -4 C.

7.3 How do plants cope?

• Cacti store water in their stems and use it slowly.
• Bushes grow few leaves or large root systems.
• Short-lived plants finish their life cycle in a few weeks, only when rain falls.

7.4 What is the Indian example?

The Thar Desert in western Rajasthan. Down To Earth says sand dunes cover about 48 per cent of the area. Rain is scanty, and drought comes every two to three years.

8.1 Where is the tundra?

Tundra lies just below the Arctic ice caps. It spreads across North America, Europe and Siberia. Much of Alaska and about half of Canada are tundra.

8.2 What is it like?

Tundra is the coldest biome. Yearly precipitation is only 150 to 250 mm, so it is like a desert.

Permafrost is its defining feature. Winters are long and dark. The mean temperature stays below 0 C for six to ten months.

8.3 What grows there?

Mosses, sedges and lichens are common. Few trees grow. Those that do stay close to the ground, where snow insulates them in winter. The word tundra comes from a Finnish word for a treeless plain.

8.4 Is tundra only near the poles?

No. NASA says tundra also occurs at the tops of very high mountains elsewhere in the world. That is why the Himalaya has a look-alike zone high up.

India has no Arctic tundra. Above the forest line, the Great Himalayan National Park has an alpine zone of grasses, herbs and low shrubs such as juniper.

9.1 Can one mountain hold many biomes?

Yes. The Great Himalayan National Park in Himachal Pradesh shows it. IUCN says it includes twenty-five forest types.

Closed forest rises from the valley floor to 3,300 to 3,600 m, depending on the slope. Higher up lie birch, stunted fir and rhododendron. Then comes the alpine zone.

9.2 Where does the tree line sit?

A little over half the park lies above 4,000 m. That height is about the upper limit of subalpine and alpine scrub in this part of the Himalaya.

So climbing a mountain is a bit like travelling toward the pole. Plants change in the same order.

10.1 How do the biomes compare?

Use this table for quick revision. Match each biome to its rain and its Indian example.

Sources: NASA Science; UC Museum of Paleontology; IUCN; Great Himalayan National Park; Down To Earth.

10.2 What pattern should you remember?

More rain and more warmth give more tall, leafy plants. Less rain or more cold gives grass, shrubs or moss. Fire, drought and winter each shape what survives.

11.1 Which mix-ups come up?

• Prairie matches Steppe. Both are temperate grassland.
• Chaparral, maquis, fynbos, mallee. Match each to its place.
• Deciduous forests lose leaves at the end of the growing season, not in summer.
• Coniferous forest lies between tundra and deciduous forest.
• Belarus has no Arctic tundra, unlike the USA, Russia and Canada.
• Tundra is wet, not dry, even with desert-like rain.
• Deserts are cold at night.