Structure of Rainforests
The Emergent Layer
This layer describes the umbrella-like upper branches of the very tallest rainforest trees, which emerge from the main canopy of leaves and branches and often reach heights of greater than 60m (200ft) [1]. The emergent trees can be quite far apart and do not form a continuous layer like the canopy. Despite extreme weather conditions, such as intense heat, strong winds and heavy rain, the emergent layer is home to many forms of life, including butterflies, gliders, eagles, small monkeys, bats, snakes and insects.
The Canopy Layer
Canopy trees grow to around 30-40m (100-130 ft). These trees' branches are packed very closely together, creating a ‘ceiling' of foliage, or canopy, below the emergent layer. Although branches from several trees may overlap, they never actually touch each other, which some scientists believe may have evolved to hinder the passage of infectious disease and parasites. The canopy consists not just of trees, but also of lianas (climbing vines, such as rattan) and epiphytes, plants that root on tree trunks and branches, including many species of orchid.
The billions of leaves in the canopy compete for sunlight, resulting in dense foliage that shades the forest floor from sunlight, as well as protecting it from heavy rains and possible soil erosion. The leaves act as mini solar panels, using the energy in sunlight for converting atmospheric carbon dioxide and water into oxygen and simple sugars, a process called photosynthesis. This exchange of gases means that the canopy layer has an effect on both local and global climates, removing carbon from the atmosphere and storing it.
The canopy layer contains a multitude of fruit and seeds, providing an excellent food source for the many animals that dwell there, including insects, primates, bats and birds, many of which are unknown to science. For example, a canopy crane set up in Australia enabled the identification of over 15,000 new insects in just four years. An estimated 70-90 percent of rainforest life lives in the canopy layer [4].
The Understorey Layer
From halfway to two thirds down the height of the tallest trees is the understorey layer, where little sunlight, perhaps only 3% of that reaching the canopy, penetrates [5]. Because of the lack of light, the understorey is quite sparse. The smaller trees with thin trunks found in this layer remain at around 20m (66 ft) tall, often "waiting" decades for a big tree to die and leave a gap that provides them with the light they need to grow into the canopy. The conditions of the understorey are quite sheltered and the dark humid environment is a haven for insects as well as birds, butterflies, frogs, lizards and snakes and predators such as jaguars and leopards.
The Shrub Layer
This layer, sometimes considered to be part of the understorey layer, lies between the understorey and the forest floor, at around 8m (25 ft) high. A plethora of tree ferns, ferns and shrubs thrive here and many of these plant species have medicinal properties.
The Floor Layer
As only around 2% of available sunlight reaches the dark, humid forest floor [1], this layer can be relatively free from dense vegetation, with just a few vines and tree seedlings thriving. Instead, detritus feeders (or detritivores), such as millipedes, woodlice, dung flies, fungi and a host of micro-organisms consume and decompose dead plants and animal parts on the forest floor. By breaking down this organic matter, nutrients are released back into the soil, and can be absorbed by the roots of the rainforest trees as part of an ongoing nutrient recycling system.
The moist, dark climate of the forest floor provides a habitat for many species, including, beetles, frogs, lizards, snakes (such as the giant Anaconda), termites, insects, and many larger animals such as the giant anteater, apes and even elephants.
