The canopy can be described as the seal on the rainforest. If there is no seal, then there is no rainforest.
It is the search for light that creates the canopy.
The rainforest canopy may be as high as 45 m above the floor. Its height is controlled by competition. If there are a few high trees, then others will be forced to grow taller too.
It may be even or uneven with several layers of trees, and if a gap appears in the top layer, wait-a-while and adjoining trees will be fast to plug up the holes in their competition for light.
The canopy provides an enormous food source for the many insects, birds, possums, and other creatures, as well as a habitat for some tree-dwelling species such as the snake. The large quantities of epiphytes provide more habitats for lizards, birds and other small animals.
In young rainforests there are generally many small trees and in old rainforests there are generally fewer but larger trees. As one tree dies or is removed, others will grow up and fight for the available light.
Giant emergent trees often project well above the canopy and reach even more impressive heights, spreading their crown over it. Leaves are of great variety, differing in shape, size, texture and colour. These sometimes provide food for species like the ringtail possum and tree-kangaroo.
Fruits are also an important food source for many fruit and seed-eating canopy-dwellers. The pericarp (outer fruit case) may be soft and succulent or hard and woody. It may enclose one or many seeds. Fruit-eating pigeons, bowerbirds, and flying foxes eat succulent fruits whereas parrots eat harder woody nuts and seeds. Indigestible seeds voided by the birds will germinate in a tree crevice or hole.
Most tree seedlings have to start their struggle for survival on the forest floor. Others, such as the strangler fig, begin life as an epiphyte in the canopy, slowly growing and putting out long cable-like roots that travel down the trunk of the host tree to the soil beneath. This allows it to readily absorb nutrients and water so it can flourish.
Mistletoes, partial parasites that also start life up in the canopy, have developed a fascinating way of ensuring the dispersal of their fruits. Mistletoebirds and other fruit eating birds eat its soft berries. These berries have sticky seeds inside that when digested and gotten rid of as waste stick to a branch and germinate.
Flowers in the canopy often provide a contrast to the colours of the dense green background. Their size, shape, colour and scents are considerably different, and are designed to attract nectar-feeding tree-dwellers to ensure their pollination. This may be from butterflies, bees, lorikeets, and other species during the day and from moths, blossom bats, flying foxes and others during the night.
Some species of the Wet Tropics are the Northern Silky Oak, Brown Silky Oak and Ivory Curl Flower.

Between the forest floor and the canopy is called the understorey.
It supports many plant species including the rainforest trees, ground ferns, tree ferns, zamias, cunjevois, cordylines or palm-lilies, native bananas, palms, climbing plants and epiphytes.
Epiphytes (lichens, mosses, ferns and orchids) use trees for attachment purposes only, and do no hurt their host. Their roots absorb moisture from rainwater as it runs downs tree trunks, and nutrients from rotting vegetation trapped by the epiphytic structure itself or from crevices in the tree.
Large tree branches in the understorey support many ferns such as the Bird’s Nest, Elkhorn, Staghorn and Basket Fern. These can reach great sizes and provide excellent catchment areas for falling leaves and plant debris. This rotting plant material then provides the fern with nutrients while supporting a miniature community of its own. Insects and other small creatures thrive in these damp aerial micro-habitats and frogs and reptiles commonly shelter within the foliage.
Tropical rainforests in high rainfall and cloudy areas support the greatest abundance and diversity of epiphytic ferns, as most prefer shady situations beneath the canopy.
Most orchids also grow in shady conditions as epiphytes in the understorey. There are about 150 species that have been recorded in the Wet Tropics, with at least 25percent of them being endemic to the region.
Their brightly coloured flowers attract insect pollinators such as wasps, bees, moths and butterflies. They all have similar structures – three inner petals and three outer sepals. Usually one petal is larger and acts as a landing platform for the pollinator.
Hundreds of tree trunks of all shapes, sizes and colours can be seen in the understorey, their bark often decorated with epiphytic lichens and mosses giving it a mottled appearance. Trunks may be smooth, ridged, furrowed or noticeably bumpy.
There are also many palm trees that are found in the Wet Tropics, several of them endemic. One is the Atherton Palm found only in rainforest above 800m altitude, and another is the majestic palm found only in dense upland regions.
The Lawyer Vine (Wait-a-While) is a palm without a large woody trunk. It is a climber with long wiry stems that have hooks growing out and upward from axils of the leaves to help grip as a climbing aid.
There are many other climbing plants that can be seen in the understorey too. The seeds of climbing plants germinate on the forest floor, and the successful seedlings grow up (with the support from a host tree) towards the light they need to survive until maturity.
Many animal species are supported by the diversity of plant life in the understorey. Some of the understorey invertebrates are moths, butterflies, bees, ants, flies, preying mantids, stick insects, beetles, crickets, cicadas and spiders. These are preyed upon by skinks, geckos, monitors and birds (eg. robins, fantails, scrubwrens, gerygones, shrike-thrushes and treecreepers). Other birds such as pigeons and bowerbirds build their nests in sites amongst the understorey.

The forest floor is home to old fallen leaves and fruits, rotten branches, ancient or diseased trees, mosses, lichens, fungi and many animal species.
Mosses of different greens cover the fallen tree trunks, which as they rot, also find bracket shaped fungal fruiting bodies growing on them. The fungi contain millions of microscopic single-celled reproductive spores, which are dispersed by wind, rain-splash, animals or by the fruiting body itself by exploding when mature. Many fungi look like the familiar mushroom, but others can be unusually shaped, resembling corals, staghorns, shells, tongues or slimes. Bright colours often add to the forest floor, as they may be red, yellow, orange, purple, blue or even luminescent at night.
Fungi and bacteria break up the rotting vegetation into smaller pieces and make food available for many creatures.
Living within leaf litter are the worms, springtails, amphipods, mites, millipedes and snails who graze upon small bits of detritus, which breaks it down further.
Seeing leaf skeletons on the forest floor is an indication that the nutritious soft, once green parts of the leaf have been digested away by both fungi and small detritivores.
To further speed up the breakdown process, rainforest cockroaches and beetles feed directly upon rotting wood.
At the same time as receiving their own nourishment, the decomposers release the important nutrients from the dead plant material through their own body waste and when they die, their own bodies. Tree roots can then recycle the nutrients as they absorb them from the soil for new plant growth.
The plant roots generally grow on or just beneath the forest floor as this is where the nutrients are concentrated. Shallow roots are therefore more efficient than deep roots in rainforest environments. The systems extend out horizontally either from the trunk base or from buttresses at the base of the tree.
Buttresses comprise woody flanged extensions that radiate outwards from the lower part of the tree base. They can reach enormous proportions around the base of a tree – they may even be 10 m high. They help support a tree’s weight in the shallow soil by taking up strains and stresses.
Continuing the food web, carnivorous invertebrates (eg scorpions, spiders and beetles) feed on tiny detritivores. In turn, these are then food for larger ground-dwelling carnivores such as frogs, skinks, birds and mammals. The larger. Warm-blooded animals provide food for blood-sucking leeches.
Birds such as chowchillas, whipbirds, scrubwrens and fernwrens search for small invertebrates in the leaf litter during the day. At night, bandicoots nose their way through the litter and rotting logs looking for grubs, native rats search for fruits and small invertebrates, and rainforest dingoes stalk any suitable prey.