Terrestrial Biomes
Terrestrial Biomes Overview
Definition of a Biome
- A biome is a type of terrestrial ecosystem unique to a specific region characterized by distinct vegetation types.
- Associated with varying temperature and moisture conditions.
- Categorized based on average annual temperature, precipitation, and their variation.
Biome Characteristics
- Biomes are geographic regions housing communities of organisms with similar adaptations due to convergent evolution.
- Similar adaptations arise from unrelated species evolving under comparable selective forces.
Major Temperature Ranges in Biomes
- Biomes are grouped based on temperature:
Climate Diagrams
- Climate diagrams: Visual graphs plotting average monthly temperature and precipitation for specific locations.
- Growing season: Months suitable for plant growth (temps > 0°C).
- Plant growth constrained when temperature falls below or rises above certain precipitation levels.
Description of Major Biomes
1. Tundra
- Coldest biome, dominated by treeless expanse above permafrost.
- Low plant diversity; upper soils thaw during a brief summer growing season.
- < 600 mm precipitation; soils are acidic and nutrient-poor.
- Plants grow close to the ground for protection from harsh conditions.
2. Boreal Forest
- Characterized by evergreen, needle-leaved trees; short growing season, severe winters.
- Temperatures can drop below 5°C (as low as -60°C); rainfall ranges from 50–1,000 mm.
- Forms largest organic carbon reservoir due to slow decomposition.
- Species diversity is low, important for lumber and paper industries.
3. Temperate Rainforest
- Known for mild temperatures and abundant rainfall; dominated by evergreen forests.
- Warm conditions influenced by nearby ocean currents.
- Common species include coast redwood and Douglas fir, growing up to 60–70 m tall.
4. Temperate Seasonal Forest
- Moderate temperatures and precipitation; dominated by deciduous trees (e.g. maple, beech, oak).
- Conditions fluctuate due to distance from warm ocean currents; precipitation exceeds transpiration.
- Acidic and podsolized soils support vegetation under dominant trees.
5. Woodlands/Shrublands
- Characterized by hot, dry summers, mild, wet winters.
- Supports drought-tolerant grasses and shrubs (often called Mediterranean climate).
- 12-month growing season; frequent fires limit plant growth.
6. Temperate Grasslands / Cold Deserts
- Hot, dry summers and cold winters feature grasses and drought-adapted shrubs.
- Soils are nutrient-rich, low in acidity; organic matter abundant.
- Cold deserts prevail where precipitation is less than 250 mm.
7. Tropical Rainforests
- Warm and rainy (>2,000 mm annually); diverse vegetation layers.
- Canopy features 30–40 m trees, high species diversity.
- Rapid decomposition; poorly retains nutrients in soils.
8. Tropical Seasonal Forests/Savannas
- Warm temperatures with distinct wet and dry seasons; dominated by deciduous trees.
- Savannas consist of grasses and a few trees; fire and grazing maintain ecosystems.
- Soil less nutrient-retentive; warm climate favors quick growth.
9. Subtropical Deserts
- Hot temperatures, scarce rainfall, and long growing seasons characterize these areas.
- Associated with Hadley cell dynamics; shallow, nutrient-poor soils.
- Supports succulents like cacti, shrubs, and some small trees.
Conclusion
- Differences in climate (temperature, precipitation, soil types) determine dominant plant forms within biomes.
- Plants and animals have evolved special adaptations to thrive in their respective environments.