Tropical rainforests: biodiversity, deforestation and management

OCR J383 Paper 2 tests the rainforest topic with case-study questions and 8-mark evaluate questions about management. You need to know why rainforests are biodiverse, why they are being destroyed, and how destruction can be managed sustainably.

Characteristics and biodiversity

Location: tropical regions (10°N–10°S of equator); Brazil, DRC, Indonesia, Malaysia.

Climate: hot (25–30°C year-round); very wet (2,000–10,000 mm rainfall/year); no dry season. Temperatures and rainfall are high because the equator receives direct solar radiation year-round.

Layered structure:

• Emergents (50–80 m): giant trees above the canopy; waxy leaves to shed heavy rain.
• Canopy (25–45 m): dense, continuous layer; most animal species live here.
• Under-canopy/shrub layer (5–15 m): plants adapted to low light; large leaves to maximise photosynthesis.
• Forest floor: dark; leaf litter; home to large animals and decomposers.

Biodiversity: tropical rainforests cover 6% of Earth's land surface but contain over 50% of all species. High biodiversity is due to:

• Year-round warmth and moisture → continuous plant growth.
• Stability over millions of years → long time for species to evolve and specialise.
• Huge variety of ecological niches (different layers, light levels, food sources).

The nutrient cycle

The critical difference from temperate forests: nutrients are NOT stored in the soil — they are stored in the living biomass (trees, plants, animals).

The cycle:

1. Dead organic matter (leaves, animals) falls to the forest floor.
2. Decomposers (bacteria, fungi) break it down rapidly (heat + moisture accelerate decomposition).
3. Nutrients are quickly absorbed by shallow tree roots.
4. Trees grow and store nutrients in their biomass.

Why deforestation is so damaging: when trees are removed, the nutrient store is removed. Rain leaches remaining nutrients from the exposed, thin soil → soil becomes infertile within a few years of clearing.

Causes of deforestation

Cause	Example
Commercial cattle ranching	Brazil: soya/beef for export; 80% of Amazon deforestation
Logging	Hardwood timber (mahogany, teak) for export
Mining	Gold, iron ore (Carajás complex, Brazil)
Road building	Trans-Amazonian Highway opened interior to settlers
Hydroelectric power	Belo Monte Dam (Brazil) flooded large areas
Population growth	Subsistence farming; transmigration (Indonesia)

Consequences of deforestation

• Biodiversity loss: species extinction; keystone species removed.
• Climate change: forests absorb CO₂; deforestation releases it; reduced transpiration.
• Soil erosion: without tree roots to anchor soil, rain erodes it.
• Hydrological cycle disruption: less interception → more surface runoff → flash flooding.
• Indigenous people: displacement and cultural destruction (e.g. Kayapo people, Amazon).

Sustainable management

Strategy	How it works
Selective logging	Only certain trees cut; allows forest to recover
Ecotourism	Income from tourism; protects forest as an economic asset
Agro-forestry	Growing crops among trees; maintains some forest structure
Buffer zones	Protected areas around national parks; controlled access
International agreements	REDD+ (UN): payments to countries that protect forests
Debt-for-nature swaps	Wealthy countries cancel debt in exchange for forest protection
Education and enforcement	Ranger programmes; community involvement

Case study: Amazon (Brazil)

• Amazon covers 5.5 million km²; 60% in Brazil.
• Deforestation rate: 11,000 km²/year (2019–20 under Bolsonaro's government — increased significantly).
• Brazil's Forest Code (2012): requires farmers to keep 80% of their land as forest in the Amazon region.
• Funai agency: protects indigenous groups.
• Deforestation fell by ~80% between 2004 and 2012 through monitoring and enforcement — then rose again.

Common OCR exam mistakes

1. Saying the Amazon soil is very fertile — the opposite is true; nutrients are in the biomass, not the soil.
2. Forgetting the role of transpiration in the water cycle — trees release water vapour, contributing to local rainfall; deforestation reduces this.
3. Not being able to suggest specific sustainable management strategies with examples — "protect the rainforest" earns nothing.