Syllabus Edition
First teaching 2015
Last exams 2025
What are Biomes? (DP IB Environmental Systems & Societies (ESS))
Revision Note
Biomes
Biomes Definition
Biomes are large-scale ecological communities that are characterised by their dominant vegetation, climate, and other abiotic factors that shape their biotic communities
Biomes are classified into five major classes:
Aquatic
Forest
Grassland
Desert
Tundra
These major classes can be divided into further categories, for example:
Aquatic biomes are water-based ecosystems that are divided into freshwater and marine ecosystems, including lakes, rivers, oceans, and coral reefs
Forest biomes are dominated by trees and are categorised into tropical rainforests, temperate deciduous forests, and boreal forests
Grassland biomes are characterised by grasses and herbaceous plants and are categorised into savannas and 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 subcategories such as hot deserts, cold deserts, coastal deserts, and semi-arid deserts
Tundra biomes are found in high latitudes and are characterised by low temperatures and permafrost - they can be further divided into subcategories such as arctic tundra and alpine tundra
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
Characteristics | Tropical Rain Forest | Temperature Forest | Boreal forest |
Location | Low latitudes Within the Tropics 23.5° north and south of the equator Amazon in South America, New Guinea, Southeast Asia, Zaire Basin | Between 40°- 60° north and south of the equator | Between 50°- 60° north and south of the equator |
Annual Precipitation | Over 2000mm | 750-1500mm (all year round) | 300-900mm (all year round) |
Temperature Range | 26-28°C | Over 0° C in winter and summer between 20°C-25° C | -30°C in winter and 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 | Infertile due to leaching and rapid uptake of nutrients by plants | Fertile soils | Not very fertile often acidic with permafrost |
Biodiversity | Approx. 50% of the world's plant and animal species live within the rainforest biome Four layers of vegetation: mahogany, teak trees, lianas, orchids Toucans, jaguars, frogs, snakes | Wide range of animals and plants with higher biodiversity than boreal forests | Less biodiverse than temperate forests |
Grassland Biomes
Characteristics | Savanna | Temperate Grasslands |
Location | North and south of the tropical and monsoon forest biomes 5° - 30° north and south of the equator Central Africa - Tanzania, Kenya | The 'veldts' of South Africa, the 'pampas' of Argentina, and 'steppes' of Russia and the 'plains' of the USA 40°- 60° north and south of the equator |
Annual Precipitation | 800-900mm | 250-750mm |
Temperature Range | 15°C to 35°C | -40°C to 40°C |
Seasons | Wet and dry season | Four seasons |
Growing Season | During the wet season (4-5 months) | During the summer (dependent on temperature) |
Soils | Free draining with a thin layer of humus Not very fertile most nutrients near the surface | Fertile soil |
Biodiversity | Wide range of plant and animal species Grasses, baobab and acacia trees Zebras, elephants, giraffes Greatest diversity of hoofed animals | Large numbers of plant and animal species Grasses, sunflowers Bison, antelopes, rabbits Grasses and trees |
Desert Biomes
Characteristics | Hot Desert |
Location | 15° - 30° north and south of the equator North Africa - Sahara, Southern Africa - Kalahari and Namib, Australia, Middle East |
Annual Precipitation | Below 250mm |
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 |
Biodiversity | Low diversity Cacti, yucca Spiders, scorpions, camels, meerkats |
Tundra Biomes
Characteristics | Tundra |
Location | North of the Arctic Circle and Antarctica |
Annual Precipitation | Less than 250mm |
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 Snowy owls, snow bunting and tundra swan Arctic foxes, hares and wolves Polar bears, musk ox and caribou Small grasses, mosses, lichen |
The Distribution of Biomes
Insolation, precipitation, and temperature are the main factors governing the distribution of biomes
Insolation refers to the amount of solar radiation that reaches the Earth's surface and affects temperature
Precipitation affects the availability of water, which is a key limiting factor for many biomes
Temperature determines the rate of photosynthesis and respiration in plants, as well as the metabolic rates of animals
The combination of temperature and precipitation determines the distribution of biomes around the world
Precipitation and temperature are the two most important climatic variables that determine the type of biome in a particular location
Worked Example
The table below shows the net primary productivity (NPP) and species richness for three biomes: tropical rainforest, temperate deciduous forest, and tundra. Analyse the data and discuss the differences in productivity and biodiversity among the three biomes.
Biome | NPP (kJ/m2/yr-1) | Species Richness |
Tropical Rainforest | 2200 | Very high |
Temperate Deciduous Forest | 900 | High |
Tundra | 50 | Low |
Answer
The data suggest that tropical rainforests have the highest rate of photosynthesis and carbon fixation, as well as the greatest number of species, followed by the temperate deciduous forest and then the tundra. One possible reason for the higher productivity and biodiversity in the tropical rainforest and temperate deciduous forest could be the greater availability of water and higher average temperatures compared to the tundra. Higher temperature and higher precipitation contribute to the growth of plants and the cycling of nutrients The difference in temperature is due to the fact that the tropical rainforest is located near the equator, where solar insolation is high and the climate is warm and humid, while the tundra is located in the polar regions, where solar insolation is low and the climate is cold and dry.
Effect of Climate Change on Biomes
Climate change is one of the greatest threats to biodiversity on Earth
As the global climate changes, the distribution of biomes is shifting, leading to significant impacts on ecosystems and the services they provide
Biomes are collections of ecosystems that share similar climatic conditions, such as temperature and precipitation
As these conditions change, the boundaries between biomes shift, 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
Photo by Peter Burdon on Unsplash
A changing biome type in Namibia
The distribution of biomes is primarily determined by temperature and precipitation
As global temperatures rise, the boundaries between biomes shift poleward or upward in elevation
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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