Tropical rainforests and deforestation

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Notes de leçon

What is a tropical rainforest?

Tropical rainforests are dense, warm forests with high rainfall, typically found between 10° north and south of the Equator.
They lie within the torrid zone, between the Tropic of Cancer and the Tropic of Capricorn.
True rainforests have no dry season: every month averages at least 60 mm of rain.
They are a type of tropical moist broadleaf forest, which also includes seasonal tropical forests.
Seasonal tropical forests have a wet summer and a dry winter, and some trees drop their leaves in the dry season.

Climate

Mean monthly temperatures exceed 18 °C in every month of the year.
Average annual rainfall is at least 1,680 mm, often between 1,750 mm and 3,000 mm, and can exceed 10 m.
The climate is consistently hot and wet, with little seasonal variation.
High rainfall causes leaching, washing soluble nutrients out of the soil.

Layers of the rainforest

The rainforest is stratified into layers, each with its own ecosystem.
The emergent layer contains the tallest trees, which tower above the canopy.
The canopy layer is densely packed with leaves and branches and is the most populated layer.
The understory layer is shaded and rich in wildlife.
The forest floor is sparse because very little light reaches it.

Soils

Rainforest soils are nutrient-poor and acidic.
Heavy rainfall leaches soluble nutrients downwards, out of reach of most roots.
Despite poor soils, the rapid recycling of nutrients by plants supports dense forest.

Biodiversity and value

Tropical rainforests contain 40–75% of all species globally.
They are home to half of the world's animal and plant species and two-thirds of all flowering plant species.
A single hectare may contain 42,000 insect species, up to 807 trees of 313 species, and 1,500 species of higher plants.
They are called the 'world's largest pharmacy' because over a quarter of natural medicines come from them.
Many species remain undiscovered.
Rainforests are vital for carbon sequestration and climate regulation.
Indigenous peoples have lived in rainforests for millennia, relying on them for food and shelter.

Causes of deforestation

Logging removes valuable timber, often legally and illegally.
Agricultural expansion clears land for crops and pasture.
Cattle ranching is a major driver, especially in the Amazon.
Mining for minerals such as gold and iron ore destroys forest.
Roads open up remote areas to further settlement and exploitation.
Hydroelectric power schemes flood large areas of forest.

Impacts of deforestation

Habitat fragmentation and loss threaten species with extinction.
Deforestation contributes to climate change by releasing stored carbon.
It disrupts the water cycle, affecting rainfall locally and regionally.
Indigenous communities lose their homes and traditional ways of life.
Soil erosion increases when tree cover is removed.

Sustainable management

Conservation efforts focus on both preservation and sustainable use.
International programmes such as REDD and REDD+ aim to reduce emissions from deforestation and forest degradation.
Sustainable management balances conservation with human development needs.
Despite efforts, rainforests still face significant threats from deforestation and climate change.

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1.Between which lines of latitude are tropical rainforests typically found?
Easy
- A10° north and south of the Equator
- B28° north and south of the Equator
- CThe Tropic of Cancer and the Tropic of Capricorn
- D60° north and south of the Equator
2.In a tropical rainforest climate, what is the minimum average monthly precipitation?
Easy
- A60 mm
- B100 mm
- C1,680 mm
- D1,750 mm
3.Which layer of the tropical rainforest is described as densely populated and located below the emergent layer?
Easy
- AThe canopy layer
- BThe understory layer
- CThe forest floor
- DThe emergent layer
4.Why are the soils of tropical rainforests nutrient-poor?
Medium
- ABecause of leaching of soluble nutrients by heavy rainfall
- BBecause of frequent volcanic eruptions
- CBecause of low temperatures
- DBecause of a long dry season
5.Approximately what percentage of all species globally are found in tropical rainforests?
Medium
- A40–75%
- B10–20%
- C80–90%
- D25–30%
6.Which statement best describes the value of tropical rainforests as a source of medicines?
Medium
- AOver a quarter of natural medicines have been discovered in them
- BThey provide all of the world's medicines
- CThey have no known medicinal value
- DOnly a few medicines come from them
7.Which human activity is a major cause of deforestation in the Amazon?
Medium
- ACattle ranching
- BHydroelectric power
- CMining
- DLogging
8.What is the main impact of deforestation on the global carbon cycle?
Medium
- AIncreased carbon dioxide in the atmosphere
- BDecreased carbon dioxide in the atmosphere
- CNo change in carbon dioxide levels
- DIncreased oxygen in the atmosphere

Plus de questions

9.Which of the following is an example of sustainable management of tropical rainforests?
Hard
- AAgroforestry
- BClear-cutting for cattle ranching
- CBuilding new roads
- DMining
10.Tropical rainforests are found between 10° north and south of the Equator.
Easy
True or false?
11.The soils of tropical rainforests are rich in nutrients.
Medium
True or false?
12.Tropical rainforests are home to 40–75% of all species globally.
Medium
True or false?
13.Match each layer of the tropical rainforest with its description.
Medium
- Emergent layer
- Canopy layer
- Understory layer
- Forest floor
- Sparse due to low light penetration
- Towering trees that emerge above the rest
- Densely populated with trees and wildlife
- Rich in wildlife but receives less light than the canopy
14.Put the layers of the tropical rainforest in order from highest to lowest.
Medium
- Canopy layer
- Forest floor
- Emergent layer
- Understory layer
15.Which of the following are causes of deforestation in tropical rainforests? (select all that apply)
Medium
- ALogging
- BCattle ranching
- CMining
- DHydroelectric power schemes
- EReducing Emissions from Deforestation and Forest Degradation (REDD+)
16.Which of the following are impacts of deforestation on the tropical rainforest ecosystem? (select all that apply)
Hard
- AHabitat fragmentation
- BSpecies extinction
- CIncreased carbon sequestration
- DLoss of biodiversity
- EReduced leaching of soluble nutrients
17.Match each human activity with the reason it leads to deforestation in the Amazon.
Medium
- Logging
- Cattle ranching
- Mining
- Road building
- Trees are cut down for timber
- Land is cleared for grazing
- Land is excavated for minerals
- Access is created for further clearance
18.Put these layers of the tropical rainforest in order from highest to lowest.
Medium
- Emergent layer
- Canopy layer
- Understory layer
- Forest floor
19.Which of the following best describes the climate of a tropical rainforest?
Medium
- AHot and dry with a distinct winter dry season
- BHot and wet all year round with no dry season
- CWarm summers and cool winters with moderate rainfall
- DCool and wet with frequent frosts
20.Which of the following is a sustainable management strategy for tropical rainforests?
Medium
- AClear-cutting large areas for cattle ranching
- BLogging all mature trees in one operation
- CSelective logging and replanting
- DBuilding more roads through the forest
21.Why do tropical rainforest soils contain few soluble nutrients despite the heavy rainfall and dense vegetation?
Medium
- AHeavy rainfall leaches soluble nutrients out of the soil, leaving it nutrient-poor and acidic
- BThe dense canopy blocks sunlight, so dead leaves cannot decay and release nutrients
- CRainforest trees store all their nutrients in their leaves, so none reach the soil
- DThe constant high temperatures destroy nutrients before plants can absorb them
22.A rainforest is cleared and the land is used for cattle ranching. Which sequence best explains why this leads to soil erosion?
Medium
- ATree roots no longer bind the soil, so heavy rain washes the exposed topsoil away
- BCattle hooves compact the soil, which stops rain from infiltrating and causes leaching
- CRemoving trees lowers rainfall, so the soil dries out and blows away in the wind
- DCattle manure acidifies the soil, which kills the remaining plant roots
23.Which statement best explains why building new roads through a rainforest can increase the rate of deforestation?
Medium
- ARoads give loggers, miners and farmers easier access to previously remote forest
- BRoads physically cut trees down as they are constructed across the forest
- CRoads increase local rainfall, which kills trees and causes them to fall
- DRoads prevent the forest from regrowing by blocking the movement of seeds
24.Which human activity is most directly responsible for clearing large areas of Amazon rainforest to raise beef?
Medium
- ACattle ranching
- BHydroelectric power
- CEcotourism
- DSelective logging
25.Which of the following are consequences of tropical rainforest deforestation? (select all that apply)
Medium
- AHabitat fragmentation and loss of biodiversity
- BIncreased release of carbon dioxide into the atmosphere
- CIncreased leaching of nutrients from the soil
- DRising local temperatures and drier conditions
- EAn increase in the total area of rainforest worldwide
26.Which of the following statements about tropical rainforests are true? (select all that apply)
Medium
- AThey help regulate the global climate by absorbing and storing carbon
- BThey are home to around 40–75% of all species on Earth
- CThey have deep, fertile soils that are ideal for farming
- DMany indigenous peoples have lived in them for thousands of years
- EThey contain no species that are useful for medicine
27.Deforestation can reduce local rainfall because trees release water vapour into the atmosphere through transpiration.
Easy
True or false?
28.The nutrient-poor soils of tropical rainforests mean that cleared land stays fertile for many decades without fertiliser.
Medium
True or false?
29.Match each human activity to the main reason it causes deforestation in the Amazon.
Medium
- Logging
- Cattle ranching
- Mining
- Road building
- Clearing forest to extract timber for sale
- Clearing forest to create pasture for grazing
- Clearing forest to reach minerals underground
- Opening up remote forest to loggers, miners and farmers
30.Put these steps in order to show how building a road can lead to widespread deforestation.
Medium
- A road is built through remote rainforest
- Loggers, miners and farmers gain easier access
- Large areas of forest are cleared along the road
- Habitat is fragmented and biodiversity declines
31.Which statement best explains why tropical rainforests are found near the Equator?
Medium
- AThe Equator receives high and consistent solar energy all year, giving hot, wet conditions
- BThe Equator is far from the oceans, which keeps the air permanently moist
- CThe Equator lies in the rain shadow of the world's highest mountains
- DThe Equator has a strong seasonal dry season that favours dense forest
32.A true tropical rainforest climate has no dry season.
Easy
True or false?
33.A climate graph for a rainforest location shows the following average monthly precipitation, in mm: Jan 92, Feb 85, Mar 102, Apr 130, May 210, Jun 185, Jul 160, Aug 145, Sep 170, Oct 155, Nov 120, Dec 98. Does this location have a true tropical rainforest climate?
Medium
- AYes, because no month has an average precipitation below 60 mm
- BNo, because annual rainfall is too low for a rainforest
- CNo, because some months have less rainfall than others
- DYes, because the total annual rainfall exceeds 1,680 mm
34.A student writes: 'Deforestation is mainly caused by climate change, which kills trees and leads to the land being cleared for farming.' Which statement best evaluates this interpretation?
Medium
- AIt is accurate, because climate change is the main driver of deforestation
- BIt reverses cause and effect: deforestation is mainly driven by human activities such as logging and agricultural expansion, and it contributes to climate change rather than being caused by it
- CIt is accurate, because farming only happens after trees have died from drought
- DIt is inaccurate, because deforestation is caused only by volcanic eruptions
35.A map shows a rainforest reserve at grid reference 234567 on a 1:50,000 scale map. The distance between two points on the map is 4 cm. What is the real-world distance between them?
Medium
- A2 km
- B4 km
- C0.8 km
- D8 km
36.A data table shows the following changes in a rainforest region between 1990 and 2020: forest cover fell from 100,000 km² to 78,000 km²; cattle pasture increased from 15,000 km² to 40,000 km²; soy farming increased from 5,000 km² to 12,000 km²; logging roads increased from 200 km to 1,500 km. Which statements are supported by the data? (select all that apply)
Medium
- AForest cover decreased by 22,000 km² over the period
- BCattle pasture expanded more than soy farming in absolute area
- CLogging roads more than doubled in length
- DThe total area of forest increased
- ESoy farming was the largest single land use in 2020
37.An extract from a travel blog states: 'The rainforest here is so thick that the canopy blocks out almost all sunlight, and the forest floor is surprisingly open and easy to walk through.' How useful is this extract as evidence about the structure of a tropical rainforest?
Hard
- AVery useful, because it correctly describes the sparse forest floor caused by low light penetration
- BNot useful, because it confuses the canopy with the emergent layer
- CVery useful, because it proves that all rainforests have an open forest floor
- DNot useful, because it does not mention rainfall or temperature
38.A primary-source account from an early explorer describes the rainforest as having a 'dark and gloomy' forest floor with few plants. This description is consistent with the modern scientific understanding that the forest floor is sparse due to low light penetration.
Easy
True or false?
39.Match each type of evidence with what it can tell you about tropical rainforests.
Medium
- A climate graph showing monthly rainfall
- A map of global rainforest distribution
- A table of species numbers in a hectare
- A photograph of the canopy
- Whether the location has a true rainforest climate
- Where rainforests are found in relation to the Equator
- The high biodiversity of the ecosystem
- The layered structure of the forest
40.Put the following steps in order to show how evidence from a map and a data table could be used to investigate deforestation in a region.
Medium
- Identify the area of forest cover on the map for the first date
- Identify the area of forest cover on the map for the second date
- Calculate the change in forest cover between the two dates
- Compare the change in forest cover with changes in land use from the data table
- Draw a conclusion about the main cause of deforestation in the region
41.Name the layer of the rainforest that is the highest, with towering trees that emerge above the canopy.
Easy
42.What is the term for the process by which soluble nutrients are washed out of the soil by heavy rainfall?
Easy
43.Name one major cause of deforestation in the Amazon rainforest.
Medium
44.What is the minimum average monthly precipitation (in mm) for a true rainforest climate?
Easy
45.What is the minimum average annual rainfall (in mm) for a tropical rainforest?
Medium
46.Complete the sentence about the layers of the tropical rainforest.
Easy
The four main layers of the tropical rainforest are the ____, the canopy, the ____, and the forest floor.
47.Complete the sentence about the value of rainforests.
Medium
Tropical rainforests are often called the "world's largest ____" because over a ____ of natural medicines have been discovered in them.
48.What term describes the process by which soluble nutrients are washed out of the soil by heavy rainfall?
Medium
49.In a true tropical rainforest climate, what is the minimum average monthly precipitation, in millimetres?
Medium
50.Complete the sentences about the effects of deforestation.
Medium
When rainforest is cleared, the soil is no longer held together by tree ____, so heavy rain washes away the ____ soil.
51.Complete the sentence about the global importance of rainforests.
Medium
Tropical rainforests help regulate the climate by absorbing and storing ____, and they are home to around ____% of all species on Earth.
52.According to the information given, what is the minimum average monthly rainfall, in millimetres, for a true rainforest climate?
Medium
53.Explain two ways in which plants are adapted to life in the tropical rainforest.
Hard
54.Describe two impacts of deforestation on the tropical rainforest ecosystem.
Hard
55.Explain how sustainable management can help protect tropical rainforests.
Challenge
56.Explain how deforestation can affect the global carbon cycle.
Hard
57.Explain why the nutrient-poor soils of tropical rainforests are a consequence of the climate.
Hard
58.What is the minimum average monthly precipitation (in mm) for a true rainforest climate?
Easy
- A72 mm
- B66 mm
- C54 mm
- D60 mm
59.What is the minimum average annual rainfall (in mm) for a tropical rainforest?
Medium
- A2016 mm
- B1512 mm
- C1680 mm
- D1848 mm
60.In a true tropical rainforest climate, what is the minimum average monthly precipitation, in millimetres?
Medium
- A66 mm
- B72 mm
- C54 mm
- D60 mm
61.According to the information given, what is the minimum average monthly rainfall, in millimetres, for a true rainforest climate?
Medium
- A60 mm
- B54 mm
- C66 mm
- D72 mm

Notes de révision

## Tropical Rainforests — Key Facts **Location & climate** - Found between 10° north and south of the Equator; broadly within the tropics (Tropic of Cancer to Capricorn). - Hot all year: mean monthly temperatures **exceed 18 °C (64 °F)**. - Very wet: average annual rainfall **no less than 1,680 mm (66 in)**, typically **1,750–3,000 mm (69–120 in)**, and can exceed 10 m (390 in). - True rainforest has **no dry season** — every month averages at least **60 mm (2.4 in)** of rain. **Soils** - Heavy rain **leaches** soluble nutrients, leaving soils **nutrient-poor and acidic**. **Layers (stratified structure)** - **Emergent layer** — towering trees above the rest. - **Canopy layer** — densely populated; main continuous cover. - **Understory layer** — rich in wildlife, shaded. - **Forest floor** — sparse because little light penetrates. **Biodiversity** - Home to **40–75% of all species** globally; **half** of the world's animal and plant species; **two-thirds** of all flowering plants. - One hectare may hold **42,000 insect species**, up to **807 trees of 313 species**, and **1,500 species of higher plants**. - Called the **"world's largest pharmacy"** — over a quarter of natural medicines come from rainforests. **Value & threats** - Crucial for **carbon sequestration** and **climate regulation**. - Threatened by human activity: **logging, agricultural expansion, cattle ranching, mining, roads, hydroelectric power**. - Causes **habitat fragmentation** and loss, driving species extinction. - **Indigenous peoples** have lived in rainforests for millennia, relying on them for food and shelter. **Conservation** - Focus on **preservation** and **sustainable management**. - International policies: **REDD and REDD+** (Reducing Emissions from Deforestation and Forest Degradation). - Challenge: balancing conservation with human development needs. **Other tropical forests** - **Moist seasonal tropical forest** — warm wet summer, cooler dry winter; some trees drop leaves. - **Montane rainforest** — cooler mountain areas; becomes **cloud forest** at higher elevations (roughly 1500–2500 m lower limit, 2400–3300 m upper limit).

Tropical rainforest: Dense, warm rainforest with high rainfall, typically found between 10° north and south of the Equator; a type of tropical moist broadleaf forest where no dry season occurs.
Leaching: The washing out of soluble nutrients from the soil by heavy rainfall, leaving soils nutrient-poor and acidic.
Emergent layer: The top layer of the rainforest, made up of towering trees that rise above the canopy.
Canopy layer: The densely populated main layer of the rainforest, forming a continuous cover below the emergents.
Understory layer: The layer below the canopy, shaded and rich in wildlife.
Forest floor: The lowest layer, sparse because little light penetrates the layers above.
Biodiversity: The variety of plant and animal species; tropical rainforests hold 40–75% of all species globally.
Habitat fragmentation: The breaking up of a habitat into smaller, isolated patches, often caused by human activity such as logging and agricultural clearance.
Deforestation: The removal of forest, often for logging, farming, cattle ranching, mining, roads or hydroelectric power, leading to habitat loss.
Carbon sequestration: The capture and storage of carbon dioxide from the atmosphere; a key global function of tropical rainforests.
REDD and REDD+: Reducing Emissions from Deforestation and Forest Degradation — international programmes aiming to curb deforestation and forest degradation.
Sustainable management: Using and conserving rainforest resources in a way that meets present needs without damaging the forest for the future.
Moist seasonal tropical forest: Tropical forest with high overall rainfall, a warm wet summer and cooler dry winter; some trees drop leaves in the dry season.
Montane rainforest: Rainforest in cooler mountainous areas, becoming cloud forest at higher elevations.

Cartes mémo

Where are tropical rainforests typically found?

They are typically found between 10° north and south of the Equator, roughly within the 28° latitudes between the Tropic of Cancer and the Tropic of Capricorn.

What is the defining climate characteristic of a true tropical rainforest?

True rainforests occur where no dry season occurs; all months have an average precipitation of at least 60 mm.

What are the temperature and rainfall conditions in a tropical rainforest?

Mean monthly temperatures exceed 18°C in all months, and average annual rainfall is no less than 1,680 mm, typically between 1,750 mm and 3,000 mm.

Why are tropical rainforest soils nutrient-poor?

High rainfall causes leaching, which washes soluble nutrients out of the soil, leaving it nutrient-poor and acidic.

What are the four main layers of a tropical rainforest?

The emergent layer, the canopy layer, the understory layer, and the forest floor.

Which layer of the rainforest is densely populated and why?

The canopy layer is densely populated because it receives the most sunlight and supports a wide variety of plant and animal life.

Why is the forest floor sparse in a tropical rainforest?

The forest floor is sparse because little light penetrates through the dense canopy above, limiting plant growth.

How biodiverse are tropical rainforests?

They are home to 40–75% of all species globally, including half of the world's animal and plant species and two-thirds of all flowering plant species.

Why are tropical rainforests called the 'world's largest pharmacy'?

Over a quarter of natural medicines have been discovered in them.

What is a key adaptation of plants in the emergent layer?

They are towering trees that emerge above the canopy to access the most sunlight.

What are the main causes of deforestation in tropical rainforests?

Logging, agricultural expansion, cattle ranching, mining, road building, and hydroelectric power development.

What is habitat fragmentation and why is it a threat?

Habitat fragmentation is the breaking up of large habitats into smaller, isolated patches. It threatens species by reducing their habitat and isolating populations, leading to extinction.

What is the Amazon rainforest a case study for?

It is a major case study for deforestation, illustrating causes such as cattle ranching, logging, and farming, and the resulting impacts.

What are the impacts of deforestation on the environment?

Deforestation leads to habitat loss, species extinction, soil erosion, and contributes to climate change by reducing carbon sequestration.

How do tropical rainforests help regulate the global climate?

They sequester carbon and influence weather patterns through transpiration, helping to regulate global climate.

What is sustainable management of rainforests?

It involves using rainforest resources in a way that meets current needs without compromising the ability of future generations to meet their own needs, such as through selective logging and agroforestry.

What are REDD and REDD+ programs?

REDD (Reducing Emissions from Deforestation and Forest Degradation) and REDD+ are international programs that aim to curb deforestation and forest degradation by providing financial incentives to developing countries.

Why are indigenous peoples important for rainforest conservation?

Many indigenous peoples have inhabited rainforests for millennia and rely on them for sustenance and shelter; their traditional knowledge and sustainable practices can help protect the forest.

What is the difference between tropical rainforests and moist seasonal tropical forests?

Tropical rainforests have no dry season, while moist seasonal tropical forests have a warm summer wet season and a cooler winter dry season, and some trees drop their leaves in the dry season.

What are montane rainforests and where are they found?

Montane rainforests are found in cooler-climate mountainous areas, often becoming cloud forests at higher elevations, typically between 1500–2500 m and 2400–3300 m depending on latitude.

How much of the world's animal and plant species are found in tropical rainforests?

Half of all living animal and plant species on the planet are found in tropical rainforests.

What is the role of ecotones in tropical forests?

Ecotones are transition areas where different biomes merge, such as between tropical rainforest and seasonal tropical forest, allowing species to mix.

Why are tropical rainforests important for biodiversity?

They support an immense variety of species, including many that are still undiscovered, making them crucial for global biodiversity.

What is the impact of cattle ranching on the Amazon rainforest?

Cattle ranching is a major cause of deforestation in the Amazon, as large areas of forest are cleared to create pasture for cattle.

How does logging contribute to deforestation?

Logging involves cutting down trees for timber, which directly removes forest cover and can lead to further degradation through road building and access for other activities.

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