What are Biomes? (SL IB Environmental Systems & Societies (ESS))

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 Western Europe, northeast USA, Eastern Asia	Between 50°- 60° north and south of the equator Canada, Russia, Scandinavia
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 Nutrient rich due to the 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 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 Deciduous trees: beech, oak, birch Deer, rabbits, squirrels, bears	Less biodiverse than temperate forests Coniferous trees  Squirrels, bears, reindeer, wolves

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

• 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