Rainforest processes and nutrient cycling

Overview

Where a rainforest holds its nutrients, the biomass, litter and soil stores, leaching, how the forest makes its own rain, what clearance does, and how a coral reef recycles nutrients.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   Where is most of the nutrient store of a tropical rainforest held?

   Model answer

   In the living biomass — the trees and other plants themselves — rather than in the ground beneath them.

2. 2

   Which three stores are used to describe the movement of nutrients through a forest?

   Model answer

   Biomass, litter and soil, with nutrients transferred between them and lost by leaching or gained from weathered rock and rainfall.

3. 3

   Why do rainforests grow so tall on soils that are so poor?

   Model answer

   Because dead material rots within weeks in the constant heat and damp and the trees take the released nutrients straight back up before rain can wash them away.

4. 4

   What is leaching, and why does it matter in a rainforest?

   Model answer

   Heavy rain washing dissolved nutrients down out of reach of roots, which is why any nutrient not taken up quickly is lost from the ecosystem.

5. 5

   How does a rainforest generate much of its own rainfall?

   Model answer

   Trees draw water up from the ground and release vapour through transpiration, which rises, cools and condenses into the afternoon downpours.

6. 6

   What happens to the water and nutrients of a rainforest once the trees are cleared?

   Model answer

   With no leaves to intercept rain or transpire it back, water runs straight off into rivers, the air grows drier, and the exposed soil loses its nutrients within a few years.

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