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Tropical rainforests: how they work
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Tropical rainforests are the richest ecosystems on land. Everything in them depends on everything else.
Abiotic characteristics
Climate: hot (about 27 °C) all year with a small temperature range, and very wet, with heavy convectional rain most afternoons.
Soils: red latosols, deep but poor in nutrients, because heavy rain washes nutrients away (leaching).
The forest has layers: emergents, canopy, under-canopy and the shrub layer on the dark forest floor.
Soils: red latosols, deep but poor in nutrients, because heavy rain washes nutrients away (leaching).
The forest has layers: emergents, canopy, under-canopy and the shrub layer on the dark forest floor.
The nutrient cycle
Gersmehl's model shows nutrients stored in biomass, litter and soil.
In a rainforest the biomass store is by far the largest. Fallen leaves decompose very quickly in the hot, wet conditions, so the litter store is small, and plants absorb nutrients fast, leaving the soil store small.
If the trees are cleared, the nutrients are lost and the soil quickly becomes infertile.
In a rainforest the biomass store is by far the largest. Fallen leaves decompose very quickly in the hot, wet conditions, so the litter store is small, and plants absorb nutrients fast, leaving the soil store small.
If the trees are cleared, the nutrients are lost and the soil quickly becomes infertile.
Biodiversity and adaptations
Rainforests have very high biodiversity because the climate is stable and warm and wet all year, giving many niches.
Plants: buttress roots support tall trees in shallow soil; drip tips shed water; lianas climb to the light; leaves form layers.
Animals: strong limbs and tails for climbing (spider monkeys), large beaks for reaching fruit (toucans), camouflage (sloths with algae in their fur), gliding flaps (flying frogs).
Plants: buttress roots support tall trees in shallow soil; drip tips shed water; lianas climb to the light; leaves form layers.
Animals: strong limbs and tails for climbing (spider monkeys), large beaks for reaching fruit (toucans), camouflage (sloths with algae in their fur), gliding flaps (flying frogs).
Explain why rainforest soil becomes infertile when trees are cut down.
- Most nutrients are stored in the trees (biomass), not the soil.
- When trees are removed, there is no leaf litter to replace nutrients.
- Heavy rain leaches the remaining nutrients out of the bare soil.
Answer: The nutrient store is removed and heavy rain leaches the soil.
Rainforests: hot, wet, stable climate; nutrient-poor latosols; layered structure. Most nutrients are in the biomass and cycle quickly. Very high biodiversity. Adaptations: buttress roots, drip tips, lianas; animals with strong limbs, large beaks and camouflage.
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