IB Environmental Systems and Societies/Biomes

2.4 Biomes

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2.4.1 Define the term biome.

• A collection of ecosystems sharing similar climatic conditions; for example, tundra, tropical rainforest, desert.
• Int: Biomes usually cross national boundaries (biomes do not stop at a border; for example, the Sahara, tundra, tropical rainforests).

2.4.2 Explain the distribution, structure and relative productivity of tropical rainforests, deserts, tundra and any other biome.

- Tropical Rainforests:

• High productivity
• High precipitation (2500 mm yr¹) throughout the year
• High insolation
• High temperature (26 ʻC)
• Good nutrient cycling = High rate of decomposure
• Highest NPP

- Temperate Forests:

• Medium productivity
• 4 seasons (Insolation and temperature varies)
• Good growing season in the summer but limited in the winter
• High temperatures and insolation in the summer = Greater productivity
• Rainfall between 500 and 1500 mm yr¹
• Second highest NPP

- Tundra:

• Low productivity
• Lowest of precipitation (50 mm yr¹)
• Low insolation (Days are shorter)
• Low Temperature
• Poor nutrient cycling because itʼs locked in the permafrost therefore low rate of decomposure
• For 1-2 months the productivity is very high because the sun is up for almost the whole day

- Deserts:

• Very low productivity
• Low precipitation (Under 250 mm yr¹)
• High insolation, but all water is evaporated or absorbed by the ground
• Hot days & Cold nights
• Low nutrient cycle
• Species adapted to survive

- Grassland:

• Wide diversity, but low levels of productivity
• Enough precipitation to prevent deserts forming, but not enough to support forests
• Nutrient cycle is sufficient
• Insolation, precipitation and evaporation rates are balanced
• Grass can grow under the surface even in cold periods, waiting to emerge until the ground warms