Giant Kapok tree in Brazil. Click image for more photos. (Photo by R. Butler)
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THE OVERSTORY LAYER OF THE RAINFOREST CANOPY
By Rhett Butler | Last updated 30, 2012
The overstory consists of giant emergent trees that tower above the surrounding canopy. These trees are huge, at least by tropical standards, some exceeding a height of 213 feet (65 meters) with horizontal limbs that stretch over 100 feet (30 m). These trees live in a different climate from the trees of the canopy. The air is much drier and moderately strong winds blow through their branches. These overstory species have adapted to take advantage of the wind for seed dispersal and typically the seeds of these species are light and equipped with some sort of mechanism to allow the winds to carry the seeds great distances away from the parent tree. The Kapok (Ceiba), or Silk-cotton tree, of South America releases its seeds attached to cotton-like material, which drifts in the wind currents for miles before reaching earth. Before fruiting, the tree sheds all its leaves so breezes pass unimpeded through its branches. In Asia, the seeds of emergent tree species Dipterocarps are equipped with "wings" that cause the spinning seed to slow as it falls and enable it to be carried long distances by the breeze.
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Emergent tree in Venezuela
(Photo by R. Butler).
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These emergent tree species are often covered with epiphytes (non-parasitic plants which take no nutrients from the host plant but use it for support). Over 2,000 epiphytes may be found on a single tree, making up one-third of the tree's total weight and 40 percent of the leaf biomass in some forests. Lianas, too, cling in mass numbers to emergent trees with over 1,500 regularly found on a single tree, making up about 20 percent of the total leaf biomass of the forest.
The most successful and most plentiful predators of vertebrates in the canopy are the birds of prey. Each continental forest region has its own species of giant eagle characterized by short wings, a long tail, and razor-sharp talons. These birds are most abundant in the overstory where they build nests near the top of giant emergent trees and raise single hatchlings. Because these eagles generally nest in the tallest trees, which are often the most valuable timber trees, they are especially threatened by selective logging, which not only destroys their habitat and nesting grounds, but also frightens away their prey. These giant eagles fly through the canopy with great speed and agility as they hunt their prey of primates, parrots, and other large mammals. When their prey is spotted, the eagle dives beneath the canopy and attacks its prey from underneath. The harpy eagle of South and Central America is the largest of these eagles attaining a height of 3 feet (1 m) and a wingspan of 6 feet (1.8 m). Because of its size, one of the harpy eagle's favorite foods is the sloth. From Southeast Asia, although now limited to four islands in the Philippines, comes the highly threatened monkey-eating eagle (100-300 left), while the crowned eagle hails from West Africa.
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WEEKLY NEWSLETTER
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Recent news
The faster, fiercer, and always surprising sloth, an interview with Bryson Voirin
(10/25/2009) Sloths sleep all day; they are always slow; and they are gentle animals. These are just some of the popular misconceptions that sloth-scientist and expert tree-climber, Bryson Voirin, is overturning. After growing up among the wild creatures of Florida, spending his high school years in Germany, and earning a Bachelors degree in biology and environment at the New College of Florida, Voirin found his calling. At the New College of Florida, Voirin "met Meg Lowman, the famous canopy pioneer who invented many of the tree climbing techniques everyone uses today."
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(11/28/2006) Home to perhaps half the world's terrestrial species, rainforests are the most biodiverse ecosystems on the planet. However, when one strolls through the forest, this biodiversity is rarely apparent for the simple reason that most activity in the rainforest occurs in the canopy, a layer of overlapping branches and leaves some 60-120 feet off the ground. Here, a wealth of ecological niches creates opportunities for plants and animals, including species generally considered to be ground-dwellers: crabs, kangaroos, and even earthworms. Beyond housing biodiversity, the canopy is the power source of the rainforest, with billions of tree leaves acting as miniature solar panels to convert sunlight into energy through photosynthesis. Since the rate of photosynthesis of canopy trees is so high, these plants generate higher yields of fruits, seeds, flowers, and leaves which attract and support a wide diversity of animal life. Further, as the principal site of the interchange of heat, water vapor, and atmospheric gases, the canopy also plays an important role in regulating regional and global climate.
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(09/20/2005) This month's issue of The Ecological Finance Review details Greenheart conservation Company, a for-profit company that designs, builds and operates conservation based canopy walkways (canopy trails) and other nature-based attractions around the world. Operating on the premise that conservation can be economically viable, Greenheart believes that is has already become a "model of how to shift gears from an industrial to a green economy." Greenheart has developed or is developing canopy walkways in Peru, Nigeria, Madagascar, Ghana, Brazil, Guyana, the United Kingdon, and Canada.
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