Topic 2.4

Biomes

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

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.htmlhttp://www.marietta.edu/~biol/biomes/biome_main.htm

Different BiomesBIOME CLIMATE ADAPATED PLANT

LIFE

Tropical rain forest 20oCRainfall throughout the year. Short dry season

Very diverse

Savanna 25-35oCSemiarid – low rainfall in winter and heavy in summer

Perennial grasses

Temperate deciduous forest -5 – 25oCSnow in winter and moderate summer rain

Rich diversity of trees and shrubs

Grassland 0 – 25oCLow rainfall

Diverse grasses, sedges broad leaved plans

Cold desert 0 – 22oCVery low rainfall

Few species of plants and shrubs

Tundra -22 – 5oCVery low rainfall

Few species of shrubs, mosses and lichens

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

A Climograph

A Climograph

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:

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 north-easterlies 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.

The Tri-cellular Model

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?