Tropical rainforests · GCSE Geography

Physical characteristics

Climate: hot all year (about 27 °C) and very wet (over 2,000 mm of rain a year), with heavy convectional rain most afternoons. There are no real seasons.
Soils (latosols) are red and poor in nutrients, because heavy rain washes the nutrients away (leaching) and plants take them up quickly.
Layers: emergent trees (up to 50 m tall), the canopy (a dense layer of treetops), the under-canopy, and the shrub layer on the dark forest floor.
Biodiversity is extremely high: rainforests cover a small part of the Earth but are home to around half of the world's species of plants and animals.

The climate, soil, plants, animals and people all depend on each other. Leaf litter rots quickly in the warm, wet climate, and the nutrients are taken up fast by the plants.
Plants: buttress roots support tall trees in shallow soil; drip tips on leaves let heavy rain run off; lianas (woody vines) climb trees to reach sunlight; epiphytes grow on other plants to reach the light.
Animals: sloths move slowly to save energy and have algae in their fur for camouflage; spider monkeys have long limbs and tails for climbing; flying frogs glide between trees.

Causes: logging for valuable hardwood; commercial farming, especially palm oil plantations (Malaysia is one of the world's biggest producers); subsistence farming; road building; mineral extraction, such as tin; energy development (the Bakun Dam in Sarawak flooded about 700 km² of forest); settlement and population growth.
Impacts: economic development (jobs, export income and electricity); soil erosion (no roots hold the soil, and no canopy shelters it from the rain); loss of biodiversity and of indigenous people's homes; and climate change (fewer trees absorb carbon dioxide, and burning them releases it).

Rainforests provide medicines, food, timber and jobs, store huge amounts of carbon, and help to control the water cycle and the local climate.
Sustainable management: selective logging (only some mature trees are cut), replanting, conservation areas and national parks, education, ecotourism, international agreements (such as certified, sustainably logged timber) and debt reduction (swapping debt for protecting forest).

The taiga (boreal forest) is a wide belt of forest across northern Canada, Scandinavia and Russia. Winters are long and very cold, often below −20 °C; summers are short and mild; and precipitation is fairly low, with snow lying for much of the winter.
Coniferous trees such as spruce, pine and fir dominate. Their cone shape lets snow slide off, their needles lose little water, and staying evergreen lets them photosynthesise as soon as it is warm enough.
Biodiversity is much lower than in rainforests, and the soils (podzols) are acidic and poor, because needles decompose slowly in the cold.
Threats: logging for timber and paper, mining, oil and gas extraction (such as the tar sands in Alberta, Canada), hydroelectric dams, forest fires, pests and acid rain.
Protection: national parks and wilderness areas where development is limited, sustainable forestry with replanting, and certification schemes for timber.

Biodiversity: The variety of plant and animal species in an area.
Canopy: The dense layer of treetops in a rainforest.
Emergent: A very tall tree that rises above the canopy.
Buttress roots: Large roots above the ground that support tall trees.
Drip tip: A pointed leaf tip that lets heavy rain run off.
Epiphyte: A plant that grows on another plant to reach the light.
Deforestation: Cutting down or burning large areas of forest.
Selective logging: Cutting down only some mature trees and leaving the rest.
Ecotourism: Tourism that protects the environment and benefits local people.
Taiga: The cold, coniferous (boreal) forest of northern Canada, Scandinavia and Russia.