Even with all the endlessly varied life sizzling far below, the emergent layer of a tropical rainforest is among that rich ecosystem's most striking characteristics. The dominion of towering trees often bursting through low clouds, this high place is home to great birds of prey and bristling epiphytes.
The emergent layer refers to the highest level of the rainforest, comprising its very tallest trees, sometimes called the overstory. Below lies the canopy layer, a denser crowd of lower trees. This, in turn, shades the understory layer of shrubs and vines and, ultimately, the forest floor. The foliage of the emergent and canopy layers shade layers below, so that in a typical tropical rainforest the understory and forest floor are often bathed in shadow. The emergent trees, meanwhile, bask in full, fierce sunlight; this layer is usually the driest level of the rainforest.
Rainforest emergents often have huge buttressed bases to enhance support, as well as broad, oblong leaves with sharp tips to shed their environment's plentiful precipitation. The profile of a rainforest canopy will be broken by emergent trees soaring 100 to 200 feet or even more above the forest floor. Such tropical emergents are among the tallest broadleaved trees in the world, though they are outsized by the conifers of temperate rainforests such as those of the Northwest coast. Emergents blasted by lightning or partly toppled by cyclones may continue standing as dramatic snags.
In the rainforests of Southeast Asia, many of the great emergent-layer trees belong to the family Dipterocarpaceae. Indeed, according to the World Wildlife Fund, some 80 percent of the emergent trees in the lowland rainforests of the island of Borneo may be dipterocarps. These include such exceptionally lofty trees as the yellow meranti, Shorea faguetiana, which can exceed 280 feet in height. Another common Southeast Asian rainforest emergent is not a dipterocarp but a legume: the tualang, Koompassia excelsa, which may be 250 feet tall. Big legumes are widespread in the extensive rainforest of the Congo Basin in equatorial Africa. In South America, among the most towering of emergents is the kapok or ceiba, which can grow beyond 200 feet in height and spreads thick-bodied branches into a muscular canopy.
The prominence of emergent trees – their often-massive height and size – make them extremely important components of the rainforest landscape. Many other organisms take advantage of their structure: Bromeliads often nestle in the nooks and crannies of big kapok trees in the tropical Americas, for example. The harpy eagle, one of the world's largest birds of prey, ranging from southern Mexico into South America, typically nests in emergent trees. The eagle will also perch atop these rainforest giants, using their supreme vantage to scan for favored prey like monkeys, sloths and birds. Emergent trees in lowland rainforests of Borneo and Sumatra help support the impressive weight of adult orangutans, the most arboreal of the great apes.