Climate, vegetation and soil form a linked system: climate sets what can grow, vegetation supplies the dead material, and decomposition turns that material into soil. Questions ask you to explain one of these links, or to use a model to say why two places differ.
This lesson opens the module on ecosystems and environmental change. The later lessons reuse the chain you build here.
How does the chain work, step by step?
- Climate gives the temperature and the rainfall. These decide how fast plants grow and how fast dead material rots.
- Vegetation responds. Warm, wet conditions support tall, dense growth with many layers, while dry or cold conditions support sparse or low growth.
- Litter is the dead leaves, twigs and roots that fall to the ground. More growth means more litter.
- Decomposition is done by fungi and bacteria. It is fast when it is warm and moist, and slow when it is cold or dry.
- Soil is built from rock fragments plus the humus and nutrients that decomposition releases.
Add one more idea: the nutrient cycle. Nutrients move between soil, plants and litter. Which store is largest depends on how quickly each transfer happens.
Worked example
All figures are invented for practice. Place A has a mean temperature of 27 °C and 2,400 mm of rain a year.
Place B has a mean temperature of 8 °C and 400 mm of rain a year. Explain how the climate affects the soil in each place.
Place A, step by step. Warmth and rain give fast growth, so a great deal of litter falls. Warm, moist conditions make decomposition fast, so the litter rots within weeks. The plants take the nutrients up again quickly, which means most nutrients sit in the biomass and the humus layer stays thin.
Place B, step by step. Low temperature and little rain give slow growth, so less litter falls. Cold slows decomposition, so litter breaks down slowly and may build up on the surface. Little rain means few nutrients are washed out, although the plants can use only what is released.
Compare. Rain per year is 2,400 ÷ 400 = 6 times greater in A. The nutrient store in A is mainly the plants. In B the nutrient store is mainly the slowly rotting litter and soil.
The mistake to watch for
A common answer is: “The rainforest has lush vegetation, so the soil is very fertile.”
Mistaken reasoning: thick vegetation must mean rich soil.
The vegetation is thick because nutrients are recycled quickly through the plants, not because the soil stores a lot.
The correction is to ask where the nutrients are stored. In a rainforest, most are in the biomass, and the soil can be poor once the trees are removed. Say “fast recycling”, not “fertile soil”.
Check yourself
1. Give two reasons why litter breaks down faster in a warm, moist place than in a cold, dry one.
Show answer
Warmth speeds the activity of fungi and bacteria, and moisture helps them work and spread. Both increase the rate of decomposition, so litter rots faster.
2. A place has 200 mm of rain a year and sparse vegetation. Explain the link in one chain.
Show answer
Little rain limits plant growth, so vegetation is sparse. Sparse vegetation gives little litter, so the soil receives little humus.
3. Place C receives 1,200 mm of rain a year and Place D receives 300 mm. How many times more rain does C receive?
Show answer
1,200 ÷ 300 = 4 times more. Check: 300 × 4 = 1,200.
Where this leads next
Next, practise reading data about energy and land cover in interpreting a food-web or land-cover dataset. The food-web and energy-flow explorer lets you see how a change in one store moves through the others, and the statistics and distribution explorer helps with the arithmetic.
Some students follow each step in class but find it hard to build the chain alone under time pressure. Our teachers work on exactly that in online one-to-one Geography tuition.