Sustaining Ecosystems Revision Notes

Climate and Location

Tropical rainforests are situated within 23.5 degrees North and South of the Equator, in a band known as the tropics. Key climatic features include high average annual temperatures (typically 20-28°C) with little seasonal variation, and very high annual rainfall (over 2000mm) distributed throughout the year, often with daily convectional storms. This climate is influenced by the Intertropical Convergence Zone (ITCZ), where trade winds meet, forcing warm, moist air to rise, cool, condense, and form clouds and precipitation. The consistent heat and moisture are fundamental to the biome's characteristics.

Vegetation Structure and Adaptations

Rainforests exhibit a distinct vertical stratification or layering: the emergent layer (tallest trees, 50m+), canopy layer (dense, interlocking crowns, 30-45m), understory (shorter trees, lianas, epiphytes, 10-30m), and forest floor (dark, humid, sparse vegetation due to lack of light). Adaptations include buttress roots for stability in shallow soil, drip tips on leaves to shed water quickly, smooth bark to prevent water accumulation, and lianas and epiphytes to access sunlight by growing on other plants. These adaptations help plants thrive in the competitive, water-rich, but often nutrient-poor soil environment.

Biodiversity and Nutrient Cycling

Tropical rainforests are biodiversity hotspots, containing over half of the world's plant and animal species despite covering less than 7% of the Earth's land surface. This high biodiversity is supported by the stable, warm, and wet climate. Nutrient cycling is rapid: dead organic matter decomposes quickly due to high temperatures and humidity, releasing nutrients that are immediately absorbed by plants. This results in very fertile vegetation but thin, poor soils that quickly lose fertility if the forest is removed, as most nutrients are stored in the biomass rather than the soil.