Biomes (HL IB ESS OLD COURSE - IGNORE)

Revision Note

Introduction to Biomes

What are biomes?

  • A biome is a group of similar ecosystems that have developed in similar climatic conditions

    • Biomes are large-scale ecological communities or ecosystem types

    • They are characterised by their dominant vegetation, climate and other abiotic factors

    • These factors shape their biotic communities

  • Biomes cover large geographic areas

    • Multiple ecosystems can be found within a single biome

  • Biomes can be categorised into groups including:

    • Freshwater biomes

    • Marine biomes

    • Forest biomes

    • Grassland biomes

    • Desert biomes

    • Tundra biomes

  • Each of these groups has characteristic abiotic limiting factors, productivity and biodiversity

  • These groups can be divided into further categories, for example:

    • Forest biomes are dominated by trees and can be further divided into:

      • Tropical rainforests

      • Temperate forests

      • Boreal forests

    • Grassland biomes are characterised by grasses and herbaceous plants and can be further divided into:

      • Savannas

      • Temperate grasslands

    • Desert biomes are characterised by low rainfall and are dominated by cacti and other drought-resistant plants—they can be further divided into:

      • Hot deserts

      • Cold deserts

      • Coastal deserts

      • Semi-arid deserts

    • Tundra biomes are found in high latitudes and are characterised by low temperatures and permafrost—they can be further divided:

      • Arctic tundra

      • Alpine tundra

Map showing the global distribution of biomes
Biomes of the world
  • Each biome has characteristic limiting factors that affect productivity and biodiversity

    • For example, in the desert biome, water is the limiting factor for plant growth, while in the tundra biome, low temperatures and permafrost limit plant growth

Forest biomes

Forest Biomes

Characteristics

 Tropical rainforest

Temperate forest

Boreal forest

Location

Low latitudes

Within Tropics: 23.5° north and south of equator

E.g. Amazon in South America, New Guinea, Southeast Asia, Zaire Basin

Between 40°–60° north and south of equator

E.g. Western Europe, northeast USA, Eastern Asia

Between 50°–60° north and south of equator

E.g. Canada, Russia, Scandinavia

Annual precipitation

Over 2000 mm

750–1500 mm (all year round)

300–900 mm (all year round)

Temperature range

26 to 28°C

Over 0° C in winter

20 to 25°C in summer

-30°C in winter

Up to 20°C in summer

Seasons

No seasons: hot and wet all year round

Four seasons of equal length

Two main seasons: winter and summer

Growing season

All year round

6–8 months

2–3 months

Soils

Relatively infertile due to leaching and rapid uptake of nutrients by plants

Relatively fertile and nutrient rich due to decomposition of organic matter over autumn and winter

Not very fertile: often acidic, with permafrost

Shallow soil with a thick litter layer due to slow decomposition

Biodiversity

Approx. 50% of world's plant and animal species live within the rainforest biome

Example flora: mahogany, teak trees, lianas, orchids

Example fauna: Toucans, jaguars, frogs, snakes

Wide range of animals and plants with higher biodiversity than boreal forests

Example flora: deciduous trees e.g. beech, oak, birch

Example fauna: deer, rabbits, squirrels, bears

Less biodiverse than temperate forests

Example flora: coniferous trees

Example fauna: squirrels, bears, reindeer, wolves

Grassland biomes

Grassland Biomes

Characteristics

 Savanna

Temperate grasslands

Location

5°–30° north and south of equator

North and south of tropical and monsoon forest biomes

E.g. central Africa: Tanzania, Kenya

40°–60° north and south of equator

E.g." veldts" of South Africa, "pampas" of Argentina, "steppes" of Russia, "plains" of USA

Annual precipitation

800–900 mm

250–750 mm

Temperature range

15–35°C

-40 to 40°C

Seasons

Wet and dry season

Four seasons

Growing season

During wet season (4–5 months)

During summer (dependent on temperature)

Soils

Free draining with thin layer of humus

Not very fertile: most nutrients near the surface

Fertile soil

Biodiversity

Wide range of plant and animal species

Greatest diversity of hoofed animals

Grasses, baobab and acacia trees

Zebras, elephants, giraffes

Large numbers of plant and animal species

Grasses, sunflowers

Bison, antelopes, rabbits

Desert biomes

Desert Biomes

Characteristics

Hot desert

Location

15°–30° north and south of equator

North Africa e.g. Sahara, Southern Africa e.g. Kalahari and Namib, Australia, Middle East

Annual precipitation

Below 250 mm

Temperature range

Daytime temperatures can reach 50°C but average around 25°C

Night time temperatures below 0°C

Seasons

Summer and winter

Growing season

All year round

Soils

Infertile, dry

Biodiversity

Low biodiversity

Cacti, yucca

Spiders, scorpions, camels, meerkats

Tundra biomes

Tundra Biomes

Characteristics

Tundra

Location

North of the Arctic Circle and Antarctica

Annual precipitation

Less than 250 mm

Temperature range

Below 0°C for 6–10 months 

Seasons

Winter and summer

Growing season

6–10 weeks

Soils

Thin infertile soil

Permafrost

Biodiversity

Low biodiversity

Small grasses, mosses, lichen

Snowy owls, snow bunting, tundra swan

Arctic foxes, hares and wolves

Polar bears, musk ox and caribou

The distribution of biomes

  • Insolation, precipitation and temperature are the main factors that determine where a biomes is located on Earth

    • Insolation refers to the amount of solar radiation that reaches the Earth's surface

      • This affects temperature and the rate of photosynthesis in plants

    • Precipitation affects the availability of water

      • This is a key limiting factor for many biomes

    • Temperature determines the rate of photosynthesis and respiration in plants

      • It also affects the metabolic rates of animals

  • The combination of temperature and precipitation determines the distribution of biomes around the world

Factors that determine biome type
Precipitation and temperature are the two most important climatic variables that determine the type of biome in a particular location

Effect of Global Warming on Biomes

  • As the global climate changes, the distribution of biomes is shifting

    • This is leading to significant impacts on ecosystems and the services they provide

    • As climate conditions change, the boundaries of different biomes are moving

    • This is also causing changes in the plant and animal species that live there

  • Biome shifts can occur in two ways:

    • Range shifts—when species move to new areas to find suitable conditions as their current habitats become less hospitable

    • Biome type changes —when a biome transitions to a different type, such as a forest becoming a savanna or a tundra becoming a forest

  • The distribution of biomes is primarily determined by temperature and precipitation

    • As global temperatures rise due to global warming, the boundaries between biomes are shifting:

      • Poleward

      • Upward in elevation (i.e. to higher altitudes)

  • This means that the warmer biomes, such as tropical rainforests and savannas, are expanding, while the colder biomes, such as tundra and boreal forests, are contracting

  • The impacts of biome shifts are significant and far-reaching:

    • As species move to new areas or experience changes in their habitats, they may face new competition, predation, or disease

    • This can lead to declines in population numbers and even extinction in some cases

    • Biome shifts can also have impacts on the vital services that ecosystems provide to living organisms, especially humans, such as water regulation, nutrient cycling, and carbon sequestration

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