Rainforest nutrient cycling, high biodiversity, and complex food webs

Why tropical rainforests have a very high rate of nutrient cycling – and how this supports biodiversity and complex food webs

Tropical rainforests (TRFs) are famous for their incredible biodiversity. A key reason is their very rapid nutrient cycling: dead material is broken down quickly, and nutrients are reused almost immediately by plants. This tight, fast cycle keeps productivity high productivity and supports complex, stable food webs.

Climate: the engine of rapid cycling

• High temperatures (around 26–28 °C all year) speed up chemical reactions and biological activity.
• High rainfall (often >2,000 mm/year) keeps the system moist, ideal for decomposers.
• Little seasonal change means there’s year-round growth, leaf fall and decomposition.

So what? Warm, wet conditions allow decomposers to work at maximum speed, releasing nutrients quickly.

Decomposers and detritivores: the rainforest’s recyclers

• Fungi and bacteria break down leaf litter, wood and dead organisms within days to weeks, not months.
• Termites, ants, beetles and earthworms shred and mix litter, increasing surface area for microbes.
• Mycorrhizal fungi (root–fungus partnerships) act like extensions of roots, supercharging nutrient uptake.

So what? Decomposition is fast and efficient, so nutrients don’t sit around—they are recycled back into living biomass quickly.

Nutrient stores and flows

• Biomass store = very large. Most nutrients are locked up in living plants (trees, lianas, epiphytes).
• Litter store = very small. Litter decomposes rapidly; there’s rarely a thick layer on the ground.
• Soil store = relatively small and often nutrient-poor. Constant uptake keeps soils depleted despite intense weathering (lateritic soils).

Key flows

• Rapid transfer from litter → soil → biomass.
• High inputs from constant leaf fall, dead organisms, and atmospheric inputs (e.g. rainfall bringing dissolved nutrients).
• High outputs via leaching in heavy rain—countered by rapid root uptake.

Plant and root adaptations that keep nutrients in play

• Shallow, wide-spreading roots (including buttress roots) sit near the surface to catch nutrients before they leach downward.
• Root mats and mycorrhizae maximise uptake of phosphorus and nitrogen the moment they’re released.
• Evergreen canopies → continuous photosynthesis and year-round nutrient demand.
• Epiphytes (plants growing on branches) trap dust and organic debris; lianas link canopy layers, helping circulate nutrients vertically.
• Drip tips on leaves shed excess water, reducing fungal growth on leaf surfaces and keeping leaves productive for longer.

So what? Plants are highly efficient at hoovering up nutrients, keeping them in the living biomass where they fuel growth.

How fast nutrient cycling boosts biodiversity

• High primary productivity (lots of plant growth) → more energy and biomass available for herbivores, then predators.
• Vertical stratification (forest floor, understorey, canopy, emergent layer) creates many niches; different species specialise at
• different heights, light levels and micro-habitats.
• Resource partitioning (e.g., different-sized beaks, night vs day activity) reduces competition, allowing many similar species to coexist.
• Mutualisms (e.g., specialised pollinators and seed dispersers) evolve in response to continuous resource availability, further increasing species diversity.

So what? Fast, continuous cycling supports a large, complex web of life, with many feeding relationships.

Complex rainforest food webs

• Producers: Tall evergreen trees, shrubs, epiphytes, vines (high productivity thanks to rapid recycling).
• Primary consumers: Leaf-eating insects, sloths, deer, and fruit-eating birds.
• Secondary consumers: Insect-eating birds, small primates, frogs, and lizards.
• Tertiary consumers/apex predators: Jaguars, harpy eagles, large snakes.
• Decomposers: Fungi, bacteria, termites, and ants recycle dead matter back into plant-available nutrients.

So what? Numerous species at each trophic level + year-round food = very complex, interlocking food webs.

The role of soils and leaching

• Despite rapid cycling, many TRF soils are nutrient-poor due to heavy rainfall leaching soluble nutrients downwards.
• The system remains productive because nutrients are held in biomass and reused quickly, not because soils are inherently rich.

So what? If the forest is removed, nutrients are lost quickly, making farming without inputs hard to sustain.