Biomes (HL IB Environmental Systems & Societies (ESS))
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
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
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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