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

These notes condense the Tropical environments study guide; go back to it for full explanations and the worked paragraph.

They cover 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. The topic is one of four Advanced Physical Geography Options assessed in Paper 3, where you answer on two of the four options. Track your progress on the Cambridge A Level Geography hub and checklist, then try the practice questions.

Paper 3 at a glance

• 1 hour 30 minutes, 60 marks, 25% of the A Level (as printed in the syllabus).
• For each of your two options: one structured question (10 marks), then one essay chosen from two (20 marks each).
• You may be asked to draw and label diagrams or sketch maps and integrate them into answers.
• The syllabus gives AO4 (evaluation) an approximate weighting of 40% on Paper 3, the largest share of any objective on this paper.
• Rough timing: 45 minutes per option, so about 15 minutes for the structured question and 30 for the essay.

Key terms

Term	Meaning
ITCZ	Low-pressure belt where the trade winds converge; rising air gives convective rain
Subtropical anticyclone	High-pressure cell near 30°N/S where air sinks, warms and dries
Monsoon	Seasonal reversal of wind direction, driven by land-sea heating contrasts and the ITCZ shift
Diurnal range	Difference between day and night temperatures
Annual range	Difference between the warmest and coolest monthly means
Hydrolysis	Reaction of minerals with water; turns feldspar in granite into kaolinite clay
Weathering front	Sharp boundary between rotted regolith and fresh rock
Corestone	Unweathered block surrounded by rotted rock
Tor / kopje	Pile of granite blocks left after regolith is stripped
Inselberg	Isolated hill rising abruptly from a plain (“island mountain”)
Bornhardt	Dome-shaped, bare rock inselberg, usually granite
Cockpit karst	Star-shaped enclosed hollows between rounded hills
Cone karst (fengcong)	Conical hills with a common base and closed depressions
Tower karst (fenglin)	Isolated steep towers rising from an alluvial plain
Climax	Stable final community in balance with climate
Subclimax	Succession halted by a natural factor
Plagioclimax	Succession deflected or held back by human activity
Pyrophyte	Plant adapted to survive fire
Ferrallitisation	Silica removed, iron and aluminium oxides left behind
Laterite	Hardened iron-rich crust (ferricrete)
Oxisol / latosol	Deep, red or yellow, highly leached rainforest soil

Climate controls in one table

Control	What it does	Effect on rainfall
ITCZ	Convergence plus convection lift moist air	Heavy rain while overhead; two peaks possible near the equator
Subtropical high	Sinking air suppresses cloud	Dry season when it extends over savanna areas
Monsoon	Onshore flow in the high-sun season, offshore in the low-sun season	Very wet summer, dry winter

Humid tropical: hot all year, annual range often only 1-3 °C, diurnal range larger than annual, rain all year. Seasonally humid: wet season under the ITCZ, dry season under the high; hottest just before the rains; larger annual range.

Landforms at a glance

Landform	Key process	Example	One evaluation point
Deep weathering profile	Hydrolysis along joints in hot, wet conditions	Granite regolith in many tropical areas	Some profiles may be relics of past climates
Tor / kopje	Two-stage: deep weathering then stripping	Kopjes of the Matobo Hills, Zimbabwe	Stripping can happen in any climate
Bornhardt	Massive, widely jointed granite resists weathering; sheeting joints keep the dome	Sugarloaf Mountain, Rio de Janeiro	Scarp retreat (Lester King) offers a rival explanation
Cockpit karst	Solution concentrated in enclosed hollows	Cockpit Country, Jamaica	Rock purity and uplift also control form
Tower karst	Lowering to the water table, then undercutting at the base	Guilin, southern China	Not always a later stage of cone karst

Inselbergs also appear in the piedmont zone of the Hot arid and semi-arid environments study guide; in this option, focus on granite and deep weathering.

Ecosystems at a glance

Idea	Rainforest	Savanna
Community status	Climatic climax	Debated: climatic climax, edaphic subclimax or fire-and-grazing plagioclimax
Structure	Emergents, canopy, understorey, shrub layer	Grass with scattered trees
Adaptations	Buttresses, drip tips, lianas, epiphytes	Deep roots, thick bark, small leaves, dry-season leaf fall
Gersmehl stores	Biomass very large; litter and soil small	Biomass smaller; soil relatively larger; litter small (fire, termites)
Flows	Large and fast	Seasonal; slow in the dry season
Productivity	Highest of any land biome	Lower; water limits growth part of the year
Soil	Oxisol / latosol	Tropical red and brown earths

Theories and studies at a glance

Who / what	Idea	Use in an answer	One evaluation point
Gersmehl (1976)	Three-store nutrient model	Explain why rainforest soils are infertile	Simplified; no time dimension
Two-stage (etching) model	Deep weathering, then stripping	Explain tors, corestones and some bornhardts	Hard to date the two stages
Scarp retreat (King)	Parallel slope retreat leaves inselbergs	Rival explanation for inselbergs	Does not explain corestones
Trophic levels	Roughly 10% energy passed upward	Explain few top predators	The 10% figure is a rule of thumb

Case study summary: Brazilian Amazon (7.4)

• Threats: cattle ranching (about 80% of clearing), soy, logging, mining, roads (Trans-Amazonian Highway, opened 1972).
• PPCDAm (2004): DETER satellite alerts, enforcement, protected areas. PRODES clearing fell from 27,772 km² (2004) to 4,571 km² (2012). Weakened after 2019; new edition June 2023.
• Soy Moratorium (2006): traders refused soy from newly cleared land; in September 2025 CADE decided to suspend it from January 2026.
• Amazon Fund (2008): BNDES-managed, mainly Norway and Germany; frozen 2019, resumed 2023.
• Mamirauá (1996): community-managed reserve of flooded forest in Amazonas state.
• Judgement: success follows political will; 6,288 km² cleared in 2024 shows recovery, but leakage to the Cerrado and weak land titles remain.

Must-know distinctions

• Annual vs diurnal range: in the humid tropics the diurnal range is larger.
• ITCZ vs monsoon: the ITCZ is a pressure belt; a monsoon is a seasonal wind reversal that the ITCZ shift helps cause.
• Inselberg vs bornhardt: every bornhardt is an inselberg, but not every inselberg is a dome of bare rock.
• Cone vs tower karst: cones share a base; towers stand alone on a plain.
• Subclimax vs plagioclimax: natural cause vs human cause.
• Biomass vs fertility: a large biomass store does not mean fertile soil.

Mini essay plan

“Savanna vegetation is the result of human activity rather than climate.” How far do you agree?

1. Introduction: define climax, subclimax and plagioclimax; locate savanna between rainforest and desert.
2. Climate case: dry season under the subtropical high; drought adaptations; savanna boundaries broadly match rainfall gradients.
3. Soil case: laterite crusts and poor drainage can stop trees (edaphic subclimax).
4. Human case: burning and grazing keep trees out; woody plants spread when fire is excluded (plagioclimax). Derived savanna on forest margins.
5. Judgement: climate sets where savanna is possible; fire and grazing decide the tree-grass balance within that zone. Agree in part.

Quick self-test

1. Why does the ITCZ give heavy rain?
2. What causes the dry season in a savanna climate?
3. Why is the diurnal range larger than the annual range in the humid tropics?
4. Which mineral in granite is broken down by hydrolysis, and to what?
5. What is a weathering front?
6. Name the two stages of the two-stage model.
7. How does a bornhardt differ from a tor?
8. How does tower karst differ from cone karst?
9. Define plagioclimax and give a tropical example.
10. In Gersmehl’s rainforest diagram, which store is largest and why?
11. Name the main soil-forming process under rainforest.
12. Give one sign that Brazil’s Amazon policies depended on politics.

Answers

1. Converging trade winds and strong heating force moist air to rise, cool and condense into cumulonimbus clouds.
2. The ITCZ moves away and the subtropical high extends over the area, bringing sinking, dry air.
3. Temperatures stay high all year, but clear nights lose heat and days gain it, so day-night differences exceed month-to-month ones.
4. Feldspar, broken down to clay minerals such as kaolinite.
5. The sharp boundary between rotted regolith and fresh rock.
6. Deep chemical weathering, then stripping of the regolith.
7. A bornhardt is a large bare dome of massive rock; a tor is a smaller pile of jointed blocks.
8. Tower karst has isolated steep towers on a flat plain; cone karst has cones sharing a base with closed hollows.
9. A community held back by human activity, such as savanna kept open by burning.
10. Biomass, because nutrients are taken up quickly and decomposition is fast.
11. Ferrallitisation.
12. Clearing rose when enforcement weakened after 2019 and fell again after a new edition of PPCDAm in 2023.

Where marks are usually lost

• Describing ITCZ movement without linking it to the timing of wet and dry seasons at a named latitude.
• Giving rainforest temperature figures but not comparing the annual and diurnal ranges.
• Explaining granite landforms without mentioning joint spacing, which controls where weathering goes deepest.
• Naming cockpit karst without describing the star-shaped hollows or the process that deepens them.
• Calling savanna “a climax” without weighing fire, grazing and soils.
• Drawing Gersmehl circles all the same size, so the diagram shows nothing.
• Saying rainforest soils are “fertile” because the vegetation is lush.
• Using the case study only as description; Paper 3 rewards judgement on how far schemes succeeded.
• Quoting figures without a year or source system (for example, PRODES annual clearing).

Official syllabus

These notes follow 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.