Nature of Biomes (AQA A Level Geography)
Revision Note
Concept of the Biome
A biome is a term for a large naturally occurring community of flora and fauna occupying a major habitat, usually at a continental scale
There are different biomes, named after its dominant vegetation and based on the climate, soil, latitude, and altitude
Each biome has its own distinct characteristics which are determined by its climate, this affects:
Length of the growing season
Temperature and precipitation levels, which in turn, impacts on the amount of plant growth
Therefore, vegetation distribution is limited by its environment
If any environmental factor changes, this will become a limiting factor in plant growth
Limiting factors are also responsible for the geography of plant distribution
E.g. cacti are only found in arid regions due to limited water supplies
Biome Distribution and Characteristics
Biome | Location | Climate Characteristics | Other Characteristics |
|---|---|---|---|
Tropical Rainforests | Low latitudes within the tropics 23.5° north and south of the equator Found in South America, Asia and Africa | Annual rainfall - 2000mm High temperatures 26-28°C Convectional rainfall | Ideal conditions for plant growth High levels of biodiversity Distinct layers of vegetation |
Tropical Monsoon Forest | 5-30° north and south of the equator Located in India, Central America and South-east Asia | Rainfall between 700-2000mm Temperatures 30-45°C in summer and 15-30°C in winter Monsoon rainfall in the rainy season | High levels of biodiversity Mahogany, teak, lianas, orchids Monkeys, Jaguars, snakes, frogs |
Mediterranean | Approximately 40-45° north of the equator Southern Europe and North Africa | Hot dry summers, wet, mild winters Temperatures usually between 20-25°C. In Winter temperatures are around 10°C Rainfall averages 800mm | Dense scrubland Vegetation includes herbs such as lavender and rosemary Trees include citrus and olives |
Deciduous Forest | Approximately 50° north of the equator Europe and North America | Wet, mild winters and warm, drier summers Average temperature around 10°C with no extremes | Deciduous trees which lose their leaves in winter due to the cooler temperatures - include oak, beech, ash Wide range of animals and plants Deer, rabbits, squirrels, bears |
Coniferous Forest | Approximately 60° north of the equator Northern Europe, Canada and Russia | Cold winters and mild summers Winter temperatures can reach -40°C and summer temperatures 20°C | Many trees are evergreen Include species such as spruce, pine Less biodiversity than temperate forests Bears, squirrels, foxes, wolves |
Savanna (tropical) Grassland | Between 15-30° north and south of the equator South America, Central Africa, Australia | Distinct wet and dry seasons Temperatures vary between 15-35°C Annual rainfall 800-900mm | Dominated by grasses Baobab and Acacia trees Savanna animals include giraffes, lions, zebras, elephants |
Temperate Grassland | Between 30-40° north and south of the equator Southern Africa, Russia, North America | Hot summers 40°C, Cold winters -30°C Annual rainfall 250-750mm a year | Dominated by grasses, very few trees Animals include bison, deer, snakes |
Desert | Approximately 20-30° north and south of the equator Africa, Australia, South and North America | Hot daytime temperatures up to 50°C but average 25°C Night time temperatures below 0°C Precipitation below 250mm | Low diversity Plants include yucca and cacti Animals include spiders, scorpions, camels |
Polar/tundra | Above 60° north and south of the equator Arctic, Antarctic, Northern Canada, Siberia | Cold year round, brief cool summers in tundra areas Below 0° C for 6-10 months Precipitation often below 250mm | Low biodiversity Short growing season Small grasses, lichens and mosses Arctic fox, polar bears, penguins, caribou |
Global Distribution of Major Biomes
Factors in global biome distribution
The distribution of biomes can also be affected by local factors including:
Climate
Soil and its ability to hold water
Slope angle - too steep and soil cannot form
Altitude
A biome's boundaries are determined by climate more than any other factor
Precipitation - areas of high pressure experience low rainfall, and areas of low-pressure experience high rainfall
The high rainfall and temperatures in equatorial areas are ideal for tropical rainforests found across Africa, south-east Asia and South America
Temperature - differences in temperature helps determine the types of plants that grow in a given area
Generally, height, density, and species diversity decreases from the warm, wet climates of equatorial regions to the cool, dry climates of the temperate and polar regions
Latitude - distance from the equator, temperatures and sunshine hours decrease
There are closer links between biomes and the climate zones - sub-Arctic tundra, European temperate forests etc.
Altitude/relief - as altitude (height) increases, the temperature falls (approx. 10°C per km)
Vegetation rates decrease as does biodiversity
Rock and soil type - soil pH (acidity/alkalinity) affects the plant species which will grow and the mineral content of soil is affected by the types of rock
Rainforest vegetation have shallow roots, as nutrients are held in the upper layer of soil due to excess leaching by its continuous humidity
Drainage - the moisture content of the soil affects the type of plant species which will grow
Plants of arid (desert) regions need to retain as much moisture as possible, so tend to be succulents
Continentality - locations further inland heat up more quickly in the summer and cool more quickly in the winter
High temperatures and low rainfalls links to semi-arid and arid (desert) regions
Ocean currents - warm and cold currents circulate in the oceans either warming or cooling the adjacent land
Marshlands, coral reefs and swamps are found along coastlines with sediment being brought on currents
Examiner Tip
The specification asks that you understand the connection between altitude (relief) and distribution of biomes
As altitude (height) increases, the temperature drops at an approximate rate of 1°C per 100m
Therefore, all vegetation must adapt to less soil, bare rock, cold temperatures, exposure to wind, etc.
These changing conditions are reflected in the vegetation type - conditions become polar the higher you go
Similarly, the further north/south you travel from the equator, the colder it gets and the vegetation changes in the same manner
So, we can say that, increases in altitude and latitude, mirror vegetation succession
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