Layers of a rainforest
Rain forests have different layers that support different animals and insects. Some plants and animals occupy specific layers, while others live and feed wherever they can. Scientists divide the rainforest into strata (zones) based on the living environment. Starting at the top, the strata are:
Above a sea of green, which is called the "upper canopy", with just a few ˇ§emergent treesˇ¨ per acre, sometimes towering as much as 200 feet above the forest floor is the tallest layer, emergent. They are like islands floating in a bright green sea of leaves. They have trunks that measure up to 16 feet around, huge mushroom-shaped crowns and very shallow roots because of the lack of nutrients in the soil. The trees establish large root systems which fan out rather than dig deep into the soil and add support and balance to fortify the tree. Most of these trees are broad-leaved, hardwood evergreens. These trees enjoy the greatest amount of sunlight but also must endure high temperatures, low humidity and strong winds. The ways in which they disperse their seedsˇXby windˇXand the creatures who inhabit themˇXbirds like the harpy eagle, and the toucanˇXare very different from those found below. Scientists build platforms in the tops of giant trees and study birds and insects that live in the canopy and the emergent layer.
This is the primary, densest, most luxuriant forest layer (60 to 150 feet above the ground) and forms a broad, tight, irregular crown. The vast carpet of green which Alexander von Humboldt called a ˇ§forest above a forestˇ¨ absorbs as much as 90% of the sunlight falling on the forest, darkening the lower regions. They also stop the rain from falling directly on the plants below. Rain must run down the trunks of the trees or drip off the leaves. The canopy is hot (reaching 32˘XC or 96˘XF) and a little drier than the understory and the forest floor ( humidity is only 60%, compared to 90% down below). Most photosynthesis occurs in the canopy where productivity is greatest: each year a tropical rainforest produces about 25-30 tonnes of new growth per acre (10-12 tons), twice as much as a temperate oak forest. The branches are often densely covered with other plants (epiphytes or air plants) and tied together with vines (lianas, which sometimes are as thick as a person). The canopy is home to 90% of the organisms found in the rain forest since food is abundant.
Understory layer (shrub / sapling layer)
Receiving only 2-15% of the sunlight that falls on the canopy, the understory is a dark place. It is relatively open and contains young trees and leafy herbaceous plants that tolerate low light. These plants have adapted to poor soil with few nutrients and seldom grow to 12 feet. They do not produce flowers helping them to conserve energy, and grow broad leaves allow the plants to take in as much light as possible. The temperature is cooler (averaging about 28˘XC or 82˘XF with humidity of about 90%) and there is a large concentration of insects here.
Forest floor (Ground layer)
The forest floor forms the lowest level in the forest. It receives less than 2% of the sunlight and consequently, little grows here except plants adapted to very low light. Only a thin layer of decaying organic matter is found, unlike temperate deciduous forests. Since hardly any sun reaches the forest floor things begin to decay quickly. A leaf that might take one year to decompose in a regular climate will disappear in 6 weeks. The floor is sometimes crowded with baby trees, called "seedlings." These little trees are working hard to grow up to the sunlight blocked by older, taller trees.