Rainforest Nutrient Cycle
How nutrients cycle through a tropical rainforest using the Gersmehl model - the biomass, litter and soil stores, the transfers between them, and why the soil is surprisingly poor.
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Lush forest, poor soil 🌴
A tropical rainforest is bursting with life, so you might expect very rich soil beneath it. In fact the soil is surprisingly **poor**. To see why, geographers follow the **nutrient cycle**. The **Gersmehl model** shows nutrients moving between three stores. In this module you will learn the stores, the transfers between them, and why clearing the forest quickly ruins the soil.
The three stores 🔑
In the Gersmehl model, nutrients are held in three stores, drawn as circles:
Match each transfer 🔗
- Uptake
- Litterfall
- Decomposition
- Leaching
- Roots absorb nutrients from the soil into the biomass
- Dead leaves fall from the biomass to the litter
- Decomposers break down litter, returning nutrients to the soil
- Water washes nutrients down out of the soil and away
Go round the cycle 🔄
An interactive activity.
The biggest store 🎯
In a tropical rainforest, which nutrient store is the largest?
- Biomass
- Litter
- Soil
- All three are the same size
Inputs and outputs ⚖️
Nutrients also enter and leave the whole cycle, not just move between stores.
Spot the losses ✅
Select the TWO processes that are outputs, taking nutrients out of the cycle.
- Surface runoff
- Leaching
- Uptake by roots
- Decomposition of litter
Why the soil is so poor 💡
It seems strange that such a green forest grows on poor soil. The reason is the **speed** of the cycle. The hot, wet climate makes decomposition and **uptake** very fast, so nutrients are pulled into the **biomass** almost as soon as they are released. Heavy rain also causes strong **leaching**, washing nutrients out of the soil. So most nutrients stay locked in the living biomass, and the soil store stays thin.
The cycle in words 🧱
In the Gersmehl model, nutrients are held in three stores. Plants absorb nutrients from the soil through their roots, a transfer called _____. When leaves and plants die, they drop to the ground to form _____. In the hot, wet climate, decomposers break down the dead material quickly, a transfer called _____. These nutrients return to the _____. The largest store in a tropical rainforest is the _____.
Transfer, input or loss? 🖍️
An interactive activity.
Clearing the forest 🧭
An interactive activity.
Explain the poor soil ✍️
An interactive activity.