November/December 2000

Life at the Top: The Rainforest Canopy

By Diane Jukofsky

The expansive, wild tangle of green for which this newsletter is named is one of the most diverse and least known ecosystems on Earth. The forest canopy is formed by the intertwining, uppermost branches of forest trees -- in a rainforest, trees that may tower more than 100 feet high.

Just as rainforests in Latin America and the Caribbean are different from those in Africa and Asia, the canopy in these forests varies -- from the intertwining branches of Latin America's forest treetops, which are bound together by plants and vines, to the narrow crowns of tropical Asia's forests, to the umbrella-shaped canopy of forests in Africa. But in all these forests, the canopy teems with life.

Until recently, little was known about life in tropical forest treetops, because getting up there was nearly impossible. Early explorers used ropes and pulleys or ladders carved into tree trunks. Today, biologists explore the canopy via towers, suspension bridges, rafts lowered gently onto treetops by dirigibles, and even construction cranes.

Biologists now know that about 90 percent of all organisms in a rainforest are found in the canopy. The sun that barely reaches the forest floor strikes treetops with full force, fueling the photosynthesis that results in leaves, fruit, and seeds. Since there's so much good food way up there, animals abound in the canopy.

Bats and birds, of course, are canopy inhabitants, though many species also fly beneath the forest ceiling, in the understory (the next level below the canopy). Insects are everywhere in the rainforest, and particularly in the canopy. Some are canopy residents; others are just passing through.

Arboreal animals, or those that live in trees -- such as monkeys (see photo at right) and lemurs -- may have prehensile tails, meaning that they can be used like a fifth appendage to grab onto branches as these animals jump and swing from tree limb to tree limb. Canopy dwellers also include many animal species you might assume stick to the ground floor such as cockroaches, mice, earthworms, and scorpions.

Other arboreal fauna are good gliders, such as flying squirrels, colugos (Cynocephalidae), Draco lizards, and flying frogs (Rhacophoridae). These animals don't actually fly, but rather control their falls, by spreading their limbs and flattening their bellies, maximizing their undersurfaces to slow their descents. Another canopy animal, the sloth (Bradypodidae and Megalonychidae), doesn't leap or glide; in fact, it barely moves at all, but clings to tree trunks and branches with razor-sharp claws.

The blooms in a rainforest canopy's garden are flowers of the trees themselves and of the plants that climb up tree trunks. But the most numerous and most spectacular canopy flowers are epiphytes, which take nutrients and moisture from the air, rather than from the soil via a root system. Epiphytes festoon tree branches, sometimes in such large numbers that the entire branch gives way from the weight. But even at the risk of loss of limb, trees can benefit from providing a home to epiphytes. Organic matter accumulates around the roots of the hitchhiking plants, creating a mass of rich soil. Trees send out roots from their branches that reach through this fertile earth and collect nutrients.

The epiphytes include orchids, bromeliads, cacti, ferns, mosses, lichens, and liverworts, totaling some 30,000 species. One tree may hold hundreds of species of orchids and more than a thousand species of epiphytes. Biologists can pick out the paths of canopy wildlife along certain tree branches that are stripped clean of epiphytes, signaling heavy traffic along a principal aerial highway.

The complex structure of the rainforest canopy allows a huge range of plant species to exist, while providing different microhabitats to wildlife, both vertebrates and invertebrates. Some scientists believe that half of the world's animal species make their airy home in the forest canopy.

From "The Encyclopedia of Rainforests", a Rainforest Alliance book by Diane Jukofsky; scheduled for publication spring 2001, Oryx Books, Phoenix.

The mission of the Rainforest Alliance is to protect ecosystems and the people and wildlife that depend on them by transforming land-use practices, business practices and consumer behavior. Companies, cooperatives and landowners that participate in our programs meet rigorous standards that conserve biodiversity and provide sustainable livelihoods.