Cambridge International AS & A Level Geography (9696): Topic 7 – Tropical environments – Study Guide

This guide covers topic 7, Tropical environments (sections 7.1 to 7.4), of the Cambridge International AS & A Level Geography (9696) syllabus for examination in 2025 and 2026. It is one of four Advanced Physical Geography Options assessed in Paper 3, which is an A Level paper. On Paper 3 you answer questions on two of the four options, so you study this topic only if your school has chosen it.

Use it with the Cambridge A Level Geography hub and the 9696 checklist. When you have finished, condense it with the revision notes and test yourself with the practice questions. Chemical weathering and the atmosphere are first taught in the AS core, so revisit the Core Physical Geography study guide before you start.

Coverage table

Syllabus reference	What you must know or be able to do (from the syllabus)	Where assessed
7.1	Global distribution and climatic characteristics of humid tropical and seasonally humid tropical environments: the roles of the ITCZ, subtropical anticyclones and monsoons	Paper 3
7.1	Key features of temperature and rainfall and their annual and diurnal variations in both environments	Paper 3
7.2	Formation of granite landforms: deep weathering profiles, tors, inselbergs and bornhardts	Paper 3
7.2	Formation of limestone landforms: tropical karst (cone karst, tower karst and cockpit karst)	Paper 3
7.3	Plant communities: development of climax, subclimax and plagioclimax; vegetation characteristics	Paper 3
7.3	Nutrient cycling: Gersmehl diagrams, soil fertility, energy flows and trophic levels	Paper 3
7.3	Soil formation: processes, soil types and profiles (oxisols/latosols, tropical red and brown earths)	Paper 3
7.4	Case study: threats to (exploitation) and problems of sustainable management of areas within either the rainforest or the savanna ecosystem, and evaluation of attempted solutions	Paper 3

How Paper 3 works

The syllabus prints these facts. Paper 3 lasts 1 hour 30 minutes, is worth 60 marks and forms 25% of the A Level. There are three questions on each option. For each of your two options you answer a structured question worth 10 marks and choose one of two essay questions worth 20 marks. You may be asked to draw and label diagrams or sketch maps and to integrate them into your answers. The syllabus gives AO4 (evaluation) an approximate weighting of 40% on Paper 3, so essays must reach judgements, not just describe.

7.1 Tropical climates

Distribution. Humid tropical (rainforest) climates lie close to the equator: the Amazon basin, the Congo basin and much of Indonesia and Malaysia. Seasonally humid tropical (savanna) climates lie towards the outer margins of the tropics on either side, for example the Llanos of Venezuela and Colombia, much of East Africa and northern Australia. Monsoon climates occur mainly in South and Southeast Asia.

The ITCZ. The intertropical convergence zone is a belt of low pressure where the north-east and south-east trade winds meet. Converging air is forced to rise. Strong surface heating adds convection, so towering cumulonimbus clouds give heavy rain. The ITCZ moves north and south through the year, following the zone of greatest heating (the overhead sun) with a lag of a few weeks. Places near the equator are under its influence for most of the year, so they have no real dry season. Some get two rainfall peaks, as the ITCZ passes over twice.

Subtropical anticyclones. Air that rises at the ITCZ flows polewards and sinks at about 30°N and 30°S. Sinking air warms and dries, so these high-pressure cells bring clear, stable weather. When the ITCZ moves away from a savanna location, the subtropical high extends over it and the dry season begins. The further a place is from the equator, the shorter its time under the ITCZ and the longer its dry season.

Monsoons. A monsoon is a seasonal reversal of wind direction. In South Asia, land heats faster than the sea in the high-sun season. Low pressure forms over the land and the ITCZ shifts far north, so moist air flows onshore and brings the wet season. In the low-sun season the land is cooler than the sea and winds blow offshore, giving a dry season.

Temperature and rainfall.

Feature	Humid tropical	Seasonally humid tropical
Mean monthly temperature	High all year, roughly 26-28 °C	High all year, with a hottest period just before the rains
Annual temperature range	Very small, often only 1-3 °C	Larger, often several degrees
Diurnal range	Larger than the annual range; cloud limits it	Large in the clear dry season, smaller in the cloudy wet season
Rainfall	Heavy all year, often 2,000 mm or more; afternoon convective storms	Distinct wet season when the ITCZ arrives and dry season under the subtropical high

A useful phrase is “night is the winter of the tropics”: in humid tropical places the difference between day and night is often larger than the difference between the warmest and coolest months.

7.2 Granite landforms

Deep weathering profiles. High temperatures and plenty of water speed up chemical reactions. In granite, hydrolysis breaks feldspar down to clay minerals such as kaolinite, while quartz grains survive. Weathering follows joints, so it reaches deepest where joints are close together. The result is a thick layer of rotted rock (regolith or saprolite) above a sharp boundary with fresh rock, called the weathering front. Unweathered blocks surrounded by rotted rock are corestones.

Tors. In the two-stage model, deep weathering first rots the closely jointed granite (stage 1). Later, a change in climate or base level lets erosion strip the regolith (stage 2). The widely jointed corestones are left standing as piles of blocks. In southern Africa such features are called kopjes.

Inselbergs and bornhardts. An inselberg (“island mountain”, a term coined by Wilhelm Bornhardt in 1900) is an isolated hill rising abruptly from a plain. A bornhardt is a dome-shaped, steep-sided, bare rock inselberg, usually granite, at least 30 m high and several hundred metres wide. Two explanations compete:

• Etching (deep weathering and stripping). Massive, widely jointed granite resists rotting while the surrounding rock weathers deeply. Stripping exposes a dome. Curved sheeting joints parallel to the surface then help keep the dome shape.
• Scarp retreat (pediplanation). Slopes retreat parallel to themselves across a plain, leaving the last remnants as inselbergs. This idea is linked to Lester King.

Example: Matobo Hills, Zimbabwe. About 35 km south of Bulawayo, this landscape is entirely granite (the Matopos batholith). It has smooth whaleback domes (dwalas), broken kopjes and balancing rocks, and was made a UNESCO World Heritage Site in 2003. It shows bornhardts and tors in the same rock, which supports the role of joint spacing. Sugarloaf Mountain in Rio de Janeiro is the classic bornhardt shape.

Evaluation. The etching model explains corestones and weathering fronts seen in road cuttings. But stripping could happen in many climates, and some granite domes stand in deserts today, so present climate is not always the cause. Many geographers now accept that both processes can operate over millions of years.

7.2 Tropical karst

Limestone dissolves by carbonation: rainwater containing carbon dioxide forms weak carbonic acid, which reacts with calcium carbonate. In the humid tropics, heavy rain and high carbon dioxide from rapid decay in the soil make solution fast.

• Cockpit karst. Star-shaped, enclosed hollows (cockpits) separated by rounded hills and ridges. Water drains down into the hollows and dissolves them deeper. In Cockpit Country, west-central Jamaica, hollows reach depths of up to about 120 m.
• Cone karst (fengcong). Many conical hills sharing a common base, with closed depressions between them. Cockpit karst is a type of cone karst in which the hollows dominate.
• Tower karst (fenglin). Steep-sided, isolated towers rising from a flat plain of alluvium. Towers form where depressions have been lowered to the water table. Swamps and rivers then undercut the bases and form foot caves, keeping the sides steep. Guilin, along the Li River in southern China, is the classic area. The South China Karst World Heritage property is described as the global type-site for fenglin and fengcong.

Evaluation. Many geographers see an evolution from cone to tower karst as the land surface is lowered towards the water table. But structure, uplift rate and rock purity matter as much as climate, so tower karst is not simply a later stage everywhere.

7.3 Plant communities

• Climax: the final, stable community in balance with climate. Rainforest is the climatic climax of the humid tropics.
• Subclimax: succession halted by a natural factor, such as poor drainage or natural fire.
• Plagioclimax: succession deflected or held back by people, for example by burning, grazing or clearance.

Savanna is the main debate. Some argue it is a climatic climax caused by the dry season. Others see it as an edaphic subclimax on poor or badly drained soils. Many see it as a plagioclimax kept open by fire set by people and by grazing. Evidence that woody plants invade when fire is excluded supports the plagioclimax view. However, savanna also exists where human influence is low, so climate and soils still matter.

7.3 Vegetation characteristics

Rainforest. Layered structure: emergents above a dense canopy, then an understorey and a shrub layer. Shallow roots and buttresses support tall trees. Drip-tip leaves shed water. Lianas and epiphytes use other plants to reach light. Evergreen, with very high biodiversity.

Savanna. Grasses with scattered trees. Many grasses die back above ground in the dry season and regrow from roots. Trees such as acacias and baobabs have deep roots, small or waxy leaves, thick fire-resistant bark (pyrophytes) and may shed leaves in the dry season (xerophytic and deciduous features).

7.3 Nutrient cycling and energy flows

Gersmehl’s model (1976) shows three stores (biomass, litter and soil) as circles sized by the nutrients they hold. Arrows show flows: litterfall, decomposition and uptake. Inputs come from weathering and precipitation; outputs leave by leaching and runoff.

• Rainforest: biomass is by far the largest store. Litter is small because decomposition is fast in hot, wet conditions. The soil store is small because nutrients are taken up quickly or leached. Flows are large and fast.
• Savanna: biomass is much smaller. The soil store is relatively larger. Litter is small because fire and termites remove it.

Soil fertility. Rainforest looks fertile but its soils are poor; most nutrients are in the plants. Clearing the forest removes the main store and exposes soil to leaching, so crop yields fall within a few years.

Energy flows and trophic levels. Producers (plants) fix solar energy. Primary consumers eat plants, secondary and tertiary consumers eat animals. Only a small share of energy (often taken as about 10%) passes to each level. Rainforest has the highest net primary productivity of any land biome; savanna is lower because water limits growth for part of the year.

7.3 Soil formation

• Ferrallitisation: intense chemical weathering removes silica in solution and leaves iron and aluminium oxides, which give a red or yellow colour.
• Leaching: heavy rain carries soluble bases down and out of the profile.
• Laterisation: iron oxides can harden into a laterite (ferricrete) crust, especially where wetting and drying alternate.

Oxisols (latosols) form under rainforest. They are very deep (often many metres), with a thin humus-rich A horizon, a deep red or yellow B horizon rich in sesquioxides and kaolinite, and low ability to hold nutrients. Tropical red and brown earths form under savanna. Leaching in the wet season is followed by upward capillary movement in the dry season, so profiles are shallower, less leached and may contain ironstone concretions. Both are less deeply weathered than oxisols. Their colour reflects how much iron oxide and organic matter they hold.

7.4 Case study: the Brazilian Amazon

The syllabus requires one case study in either the rainforest or the savanna. This guide uses the Brazilian Amazon rainforest.

Threats (exploitation). Cattle ranching is identified as the main cause of deforestation, often cited at about 80%. Soy farming, logging, mining and roads add to it. Roads open the forest: the Trans-Amazonian Highway was opened, still unfinished, in 1972, and most clearing happens close to roads.

Attempted solutions.

• PPCDAm (2004): a federal plan combining satellite monitoring (the DETER near-real-time alert system), law enforcement, land registration and new protected areas. Annual deforestation measured by Brazil’s PRODES system fell from 27,772 km² in 2004 to 4,571 km² in 2012. Enforcement weakened after 2019, and a new edition of the plan was launched in June 2023, with a target of zero deforestation by 2030.
• The Soy Moratorium (2006): traders agreed not to buy soy from land deforested after a cutoff date (later set in 2008). In September 2025 Brazil’s competition regulator, CADE, decided that it should be suspended from January 2026, which put its future in doubt.
• The Amazon Fund (2008): managed by Brazil’s development bank BNDES, funded mainly by Norway and Germany. Donors froze payments in 2019 and resumed in 2023.
• Community reserves: Mamirauá Sustainable Development Reserve (1996) in Amazonas state protects about 11,000 km² of flooded várzea forest between the Solimões and Japurá rivers, with local people living and managing resources inside it.

Evaluation. Monitoring plus enforcement worked when it had political backing, as the 2004-2012 fall shows. The rise after 2019 and the fall to 6,288 km² in 2024 show that success depends on government priorities, not technology alone. Supply-chain deals can push clearing into other areas, such as the Cerrado savanna. Community reserves give local people a stake, but they are small compared with the scale of ranching.

Worked example paragraph

Question: Evaluate the success of attempts to manage the rainforest sustainably.

In Brazil, the PPCDAm combined DETER satellite alerts with fines and new protected areas (knowledge). This targeted ranchers directly, because alerts let officials act within weeks of clearing (application). As a result, deforestation fell from 27,772 km² in 2004 to 4,571 km² in 2012, which suggests that enforcement, not just satellites, cut the profit of illegal clearing (analysis). However, enforcement weakened after 2019 and clearing rose again, so its success was fragile and depended on politics rather than lasting change in land use (evaluation).

Common errors

• Saying the ITCZ “follows the sun” exactly. It lags the overhead sun and shifts further over land than over oceans.
• Treating the rainforest’s high biomass as proof of fertile soil. The nutrients are in the plants, not the soil.
• Calling every inselberg a bornhardt. A bornhardt is a dome-shaped, bare rock type of inselberg.
• Mixing up cone, cockpit and tower karst. Towers stand isolated on a plain; cones share a common base.
• Calling savanna a climax without discussing fire, grazing and soils.
• Drawing a Gersmehl diagram without scaling the circles and arrows.
• Writing a case study with no dates, numbers or named schemes, or with no judgement of success.

Next, compare this option with Coastal environments and read the 9696 exam preparation guide for timing advice.

Official syllabus

This guide follows the Cambridge International AS & A Level Geography (9696) syllabus for examination in 2025 and 2026, topic 7 (sections 7.1-7.4). Check the latest version on the Cambridge International website; your teacher will confirm anything the syllabus does not print, including which options your school takes.