Fly across North America and you pass desert, grassland, forest and frozen tundra. Ecologists group the world's ecosystems into biomes. The question is what decides where each one is. Start from the abiotic parts in Living and Nonliving Parts.
Key idea
A biome is a large region with a similar climate (temperature and yearly rainfall) and similar kinds of plants and animals. Climate decides the plants, and the plants decide which animals can live there.
| Biome | Rain per year (about) | Temperature | Plants |
|---|---|---|---|
| Tropical rainforest | 200–450 cm | warm all year | tall broadleaf trees in layers |
| Desert | under 25 cm | hot days, often cold nights | shrubs and other plants that store or save water (cactuses in the Americas) |
| Grassland | 25–75 cm | hot summers, cold or mild winters | grasses, few trees |
| Temperate deciduous forest | 75–150 cm | four seasons | trees that drop leaves in fall |
| Taiga (boreal forest) | 30–85 cm | long cold winters | evergreen conifers |
| Tundra | 10–25 cm | very cold; frozen ground | mosses, lichens, low shrubs |
Why it works
Plants are rooted in place, so they must survive the local climate all year. Tall broadleaf trees need lots of water. Grasses survive drought and fire because they grow from the base. Conifers' needles handle snow and short summers. Animals follow their food and shelter, so they match the plants.
Worked example: Name the biome
A place gets about 15 cm of rain a year, the ground is frozen most of the year, and the plants are mosses and lichens. Which biome?
- 15 cm is very little rain: desert or tundra.
- Frozen ground and mosses and lichens mean very cold.
Answer: Tundra.
Common mistake
Students define biomes by place names ("the Sahara") or by animals ("where camels live"). A biome is defined by temperature and rainfall. Deserts exist on several continents with different animals, and they are all deserts because they are dry.