Environmental Systems and Societies

1. Topic 2.4
Biomes

2. Biosphere and Biomes
• Biosphere – Regions of the planet able to
support life
• Biome – A large patch of land with similar
conditions throughout which characteristic
plants are adapted to survive
• You can show the positions of different
biomes on a climograph

3. Biomes
• There are 3 factors which determine a biome:
– Amount of water (rainfall)
– Amount of sunlight (insolation)
– Temperature
• All of these factors affect photosynthesis
• The rate of photosynthesis determines the net primary
productivity (NPP) of a system and therefore
determines the location and make-up of a biome
http://www.windows2universe.org/earth/ecosystems.html
http://www.marietta.edu/~biol/biomes/biome_main.htm

4. DifferentBiomes
BIOME
CLIMATE
ADAPATED PLANT
LIFE
Tropical rain forest
20oC
Rainfall throughout the year. Short
dryseason
Verydiverse
Savanna
25-35oC
Semiarid– low rainfall in winter and
heavy in summer
Perennialgrasses
Temperate deciduous forest -5 – 25oC
Snow
inwinterandmoderatesummer rain
Richdiversityoftrees
andshrubs
Grassland
0 – 25oC
Lowrainfall
Diversegrasses,sedg
es broad leaved
plans
Cold desert
0 – 22oC
Verylowrainfall
Fewspecies of
plantsand shrubs
Tundra
-22 – 5oC
Verylowrainfall
Fewspeciesofshrubs
,mossesandlichens

5. http://www.marietta.edu/~biol/biomes/biome_main.htm

6. A Climograph

7. A Climograph

8. The Tri-cellular Model
• The distibution of biomes can be understood by
looking at patterns of atmospheric air circulation
• The most used model is the ‘tri-cellular’ model:

9. The Tri-cellular Model
• There are 3 cells types (one of each in the northern and southern hemisphere:
– The Hadley Cells
– The Ferrel Cells
– The Polar Cells
• In the Hadley Cells (close to the equator), air heats up, rises, then cools and
condenses, forming large cumulonimbus (rain) clouds. Pressure is low as air
rises. Due to the high temperatures and high rainfall, tropical rainforest biomes
form
• In the Ferrel Cells (approx 30o N and S of the equator), the air cools and starts
to descend. Descending air causes high pressure. Since the air has lost its
moisture, it causes desert biomes to form.
• Air now heads either back to the Hadley Cell at ground level, or to polar
regions as warm winds (south-westerlies in northern hemisphere and northeasterlies in the southern hemisphere). When the air reaches the poles, it
forms the Polar Cells (approx. 60o N and S of the equator). The air cools as it
hits colder winds. It condenses and rain falls. These conditions create
temperate forest biomes.

10. The Tri-cellular Model

11. Questions
1. What is the difference between a biosphere, a biome
and an ecosystem?
2. Make a table to show the following biomes, with
information about insolation, precipitation and
temperature for each:
- Tropical rainforest
- Desert
- Tundra
- Temperate forest
3. Which biomes have (a) the highest (b) the lowest net
primary productivity? Why?