GCSE · Geography · AQA · Spec 8035

Biodiversity issues in tropical rainforests

It looks like the richest, toughest place on Earth. But the soil is poor, and its species lean on each other so closely that one loss can pull on many.

Geography · Rainforest biodiversity

One cut, many knock-ons

What leads to what? Pick a factor, pick the factor it makes happen or makes worse, and add the link. Build as many links as you can before you compare.

  1. Deforestation: clearing forest for agriculture, logging, mining and urbanisation
  2. Logging and road building
  3. Species lose their habitat
  4. The forest is split into small, disconnected patches
  5. Populations decline; species become endangered or extinct
  6. Food chains and ecosystem services are disrupted
  7. Potential benefits for medicine, agriculture and science are lost
Add a link

No links yet.

Exam line: Chain it: name the threat, say what it does to species, then say what that loss does next. 'Roads split the forest into patches, so animals can't find mates, so populations decline.'

Geography · Rainforest biodiversity

How much life fits on 6% of the land?

Biodiversity is the variety and number of different species living in an ecosystem. Tropical rainforests cover only about 6% of Earth's land. What share of the world's plant and animal species do you think live in them? Slide to your estimate before you look.

Your estimate

50%

0%100%

Watch out: Keep the two figures apart: about 6% is a share of Earth's LAND, and about 50% is a share of the world's SPECIES. Swap them and the whole point disappears.

Why so rich? Reason 1: the climate

?

Reason it through

How does a warm, wet climate lead to so many animals?

Link 1 of 3

First link · your turn

Rainforests are warm all year and get high rainfall. What does that let plants do?

2
Locked — reveal the link above first
3
Locked — reveal the link above first

Geography · Rainforest biodiversity

What else makes it so rich?

The climate keeps plants growing all year. But climate is not the whole story of why a rainforest holds so many different species.

Which is closest to what you think right now?
How sure are you?

Geography · The nutrient cycle

Rebuild the nutrient cycle, then break it

2 stages are missing. Use the rest of the loop to work out which goes where.

  1. Stage 1: Living forest (biomass)

    The biggest store of nutrients: the living plants and animals.

  3. Stage 3: Decomposition

    Warm, wet conditions make dead material decompose quickly, releasing its nutrients.

…and stage 4 leads back to stage 1.

Exam line: Follow the loop in your answer: 'Clearing removes the biomass, so the litter is not replenished, and rain washes nutrients from the bare soil, so soil fertility declines.'

Geography · Put it together

Write it, then mark it

Explain how deforestation threatens biodiversity in tropical rainforests. [4 marks]

0 words · your answer stays on this page and is not sent anywhere.

Exam line: Every point should have a 'so': 'Trees are cleared, so species lose their habitat, so populations decline.' A threat on its own is only half a point.

WHAT YOU'VE LEARNED

A quick recap of today's lesson.

Half the world's species on a sliver of its land, and every one of them leaning on the others.

What you need to know

  • Biodiversity is the variety and number of different species living in an ecosystem.
  • Tropical rainforests cover about 6% of Earth's land but are home to about 50% of the world's plant and animal species, many found nowhere else, so they are called biodiversity hotspots.
  • Four reasons for high biodiversity: a warm, wet climate lets plants grow all year, giving lots of food for lots of animals; rainforests are ancient, so many species have had time to evolve; different layers give different conditions; and nutrients are recycled rapidly.
  • The main threats: deforestation destroys habitats; logging and road building fragment the forest; species loss spreads through interdependence; and clearing breaks the nutrient cycle.

The big picture

Tropical rainforests cover only about 6% of Earth's land but are home to about 50% of the world's plant and animal species, so they are biodiversity hotspots. A warm, wet climate, great age, layered habitats and fast nutrient recycling explain that richness. But the species depend on each other, and the nutrients are held in the living forest rather than the poor soil, so the ecosystem is delicate. Deforestation and fragmentation destroy and split habitats and push species towards extinction; the losses spread to food chains and ecosystem services, break the nutrient cycle and threaten potential benefits for medicine, agriculture and science.

Key points

1The Amazon rainforest is at least 33 million years old, which has given time for many different species to evolve.
2Rainforest species are interdependent. Some plants need animals to spread their seeds, and some animals eat only one type of plant, so if one plant species dies out an animal may have no food. This makes the ecosystem delicate.
3The largest nutrient store is the biomass and the soil is nutrient-poor. Warm, wet conditions make dead material decompose quickly, and plants rapidly take up the released nutrients.
4Deforestation is the large-scale removal or clearing of forest, for agriculture, logging, mining and urbanisation. The habitat loss it causes is why species such as the orangutan and the jaguar are classified as vulnerable or endangered.
5Fragmentation: logging and road building split the forest into smaller, disconnected patches. Isolated animals lack the space to find food, shelter or mates, which can lead to population decline and extinction.
6Many species pollinate plants, control pests and distribute seeds. Without them ecosystems could collapse, disrupting food chains and services such as soil regeneration and carbon storage.
7Clearing the forest stops dead matter replenishing the litter, and heavy rain washes nutrients from the exposed soil, so fertility declines. A drier rainforest would slow decomposition and release fewer nutrients, affecting plant growth and the whole food web.
8Losing rainforest species also affects people: many rainforest plants and animals have potential benefits for medicine, agriculture and science.

Worked example

Problem

Explain why the tropical rainforest ecosystem is described as 'delicate'. (3 marks)

⚠ Watch out

Saying rainforests have high biodiversity 'because the soil is so fertile'. It's the reverse: the soil is nutrient-poor. The nutrients are stored in the living plants and animals and recycled fast, which is exactly why clearing the forest leaves poor land behind.

🧠

Memory hook

Rich because it's WARM and WET, OLD, LAYERED and RECYCLING fast. Fragile because the treasure is in the trees, not the soil, and every species is leaning on another.

✓

Check yourself

Cover the page. Sketch the rainforest nutrient cycle as four boxes in a loop. Then say what clearing the forest does to it, and what a drier forest does.

Flashcards

(15)
What is biodiversity?
The variety and number of different species living in an ecosystem.
Why are tropical rainforests called biodiversity hotspots?
They cover only about 6% of Earth's land but are home to about 50% of the world's plant and animal species, many found nowhere else.
How does the rainforest climate lead to high biodiversity?
Warm all year + high rainfall → plants grow continuously → abundant plant growth → lots of food for lots of animals.
Why does the great age of rainforests help explain their biodiversity?
They are ancient (the Amazon is at least 33 million years old), so there has been time for many different species to evolve.
How do the rainforest's layers add to its biodiversity?
Each layer has different conditions, and different species have evolved to be adapted to each one.
Where is a rainforest's largest store of nutrients?
In the biomass: the living plants and animals. The soil is nutrient-poor.
Why are nutrients recycled so fast in a rainforest?
Warm, wet conditions make dead material decompose quickly, and plants rapidly take up the nutrients released.
Rainforest species are 'interdependent'. What does that mean for a single extinction?
One extinction can lead to others: species that relied on the lost one may be left without food, or without the animals that spread their seeds.
Define deforestation.
The large-scale removal or clearing of forest, e.g. for agriculture, logging, mining and urbanisation.
Name two rainforest species classified as vulnerable or endangered because of habitat loss.
The orangutan and the jaguar.
What is fragmentation, and why can it lead to extinction?
Logging and road building split the forest into smaller, disconnected patches. Isolated animals lack the space to find food, shelter or mates, so populations can decline and die out.
Species pollinate plants, control pests and spread seeds. What could happen without them?
The ecosystem could collapse, disrupting food chains and services such as soil regeneration and carbon storage.
How does clearing the forest break the nutrient cycle?
Dead matter no longer replenishes the litter, and heavy rain washes nutrients from the exposed soil, so soil fertility declines.
What would a drier rainforest do to the nutrient cycle?
Decomposition would slow, releasing fewer nutrients, which affects plant growth and the whole food web.
How could losing rainforest species affect people?
Many rainforest plants and animals have potential benefits for medicine, agriculture and science, so extinctions could hinder advances.

Tap any card to flip it, or use Study as deck to go through them one at a time. In the full lesson these run as a spaced-repetition deck — you rate each card Hard, Good or Easy and the tricky ones keep coming back until they stick.

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