Woodland Nutrient Cycle

A woodland through the seasons

A deciduous woodland, like an English oak wood, changes with the seasons: leaves burst out in spring and fall in autumn. Nutrients move through it in a nutrient cycle. The Gersmehl model shows that cycle as three stores linked by arrows. This module follows the cycle and, importantly, shows how a woodland differs from a tropical rainforest.

The three stores

In the Gersmehl model, nutrients are held in three stores, drawn as circles:

Match each transfer

Go round the cycle

Follow the nutrients around the cycle. Put these stages in order, starting from the soil store.

• Nutrients are held in the soil store
• Roots take the nutrients up into the trees
• The nutrients become part of the living biomass
• In autumn, dead leaves fall as litter
• Decomposers slowly return the nutrients to the soil

Why so much litter?

Compared with a tropical rainforest, the litter store in a deciduous woodland is much larger. Why?

• Leaves fall together in autumn and the cold slows decomposition, so litter builds up
• Deciduous trees never drop their leaves
• The climate is hotter, so leaves pile up faster
• There is no soil for the nutrients to go into

Rainforest vs deciduous woodland

Both biomes use the same Gersmehl model, but the sizes of the stores are very different.

Which describe a woodland?

Select the TWO statements that describe a deciduous woodland nutrient cycle.

• The three stores are more balanced in size
• A large litter store builds up after autumn leaf fall
• The biomass store completely dominates the other two
• Litter decomposes almost instantly all year round

The seasons drive the cycle

The big difference is the seasons. In autumn, deciduous trees drop all their leaves at once, so the litter store suddenly grows. Through the cold winter, decomposers work slowly, so the litter and soil stores stay larger than in a warm rainforest. In spring, nutrients are taken back up as new leaves grow. The cycle is seasonal, not constant.

Complete the cycle

The Gersmehl model shows three stores: biomass, _____ and soil. Nutrients move from soil into the trees when roots carry out _____. In a deciduous woodland, decomposition is _____ because the winters are cold. Compared with a rainforest, the three stores are more _____. When the woodland is cleared, the cycle is broken and the soil becomes less _____.

True for a woodland?

Tap the TWO statements that are TRUE for a deciduous woodland, not a tropical rainforest.

• The leaves fall together in autumn, building up the litter store.
• The biomass store is enormous and dwarfs the other two.
• Cold winters slow the decomposers down.
• Warm, wet conditions decompose the litter almost instantly all year.
• Heavy daily rain leaches most nutrients out of the soil.

Clearing the woodland

Think through what happens in and around a deciduous woodland.

• Why does the litter store reach its largest size in autumn?
• A woodland is cleared for a new housing estate. What is the main cause of this deforestation?
• After the trees are removed, what happens to the nutrient cycle?

Compare the cycles

Describe the nutrient cycle of a deciduous woodland and explain how it differs from a tropical rainforest.

• Name the three Gersmehl stores and one transfer between them
• Explain why the litter store is large in a deciduous woodland
• Describe how the store sizes differ from a tropical rainforest
• Give one cause of deciduous woodland deforestation, such as urbanisation