Rainforests comprise some of the most species-diverse and interesting biomes in the world. Tropical rainforests possess a stratified environment of various plants, represented by different layers. These layers include the ground layer, the shrub and sapling layer, the closed canopy and the emergent layer at the highest point in the rainforest. The emergent layer is home to unique plants and provides special habitat for the animals who can reach the top of the rainforest.
TL;DR (Too Long; Didn't Read)
The emergent layer of the rainforest refers to the tallest trees that emerge from the canopy of surrounding trees. Emergent trees can reach tremendous heights, and they provide unique ecosystems for animals and other plants that live among their crowns.
What Is the Emergent Layer of the Rainforest?
A rainforest’s continuous warmth and plentiful precipitation ensure the prolific growth of many plants, yielding spectacular species diversity. Among the rainforest’s different layers, the uppermost is called the emergent layer. It is from this peak of rainforest that certain trees emerge from the canopy beneath. Not every kind of tree in a rainforest can reach this lofty height. Another name for the emergent layer is the overstory layer.
The Unique Environment of the Emergent Layer
Each rainforest layer provides a different climate for the plants that live there. Living at the rainforest roof means that emergent trees soak up unrestricted sunlight compared to shaded layers below. In the emergent layer, tall trees and the plants that live on them experience drying winds, inclement weather, and the influence of animals who can reach that uppermost point. Because emergent trees experience the winds at their height, some trees species are deciduous in the limited dry season of the rainforest.
Emergent Layer Adaptations
One adaptation emergent trees have for this environment is horizontal limbs that can stretch as much as 100 feet. These trees have also adapted their seed dispersal methods for the windy environment. This helps carry the seeds far from the parent tree.
For example, the Kapok tree, also known as the silk-cotton tree, in South America uses a cottony substance for its very lightweight seeds, and they are sent in drifts along with the wind. Other species, such as the Dipterocarps in Asia, use wing-like structures that spin and send seeds parachuting away on the wind.
Emergent Trees in the Rainforest
From the ground floor of a rainforest to its very roof, the canopy, some of the tallest trees rise above the rest in the emergent layer. Emergent trees can reach heights of 100 to 120 feet tall. They possess an umbrella-like shape that spreads above the underlying canopy. The canopy below, called the closed canopy, also bears tall trees, from 60 to 80 feet in height. This makes emergent trees even more remarkable in size and scale.
The tallest emergent trees of the Amazon rainforest are quite huge. Researchers found that angelim vermehlho trees (Denizia excels) can grow over 80 meters tall; in fact, one such discovered emergent tree had reached 88.5 meters, or over 290 feet.
Researchers found these giant trees near the Jari River, a tributary of the Amazon River. That area seemed to be shielded from human development and the highest winds. The giant angelim vermehlho trees are believed to be approximately 400 to 600 years old. Scientists estimate that just one of the giant trees stores the same amount of carbon as a regular forest of 500 smaller trees. Protecting and conserving such giants is therefore a priority.
Other kinds of trees that make it to the overstory of the rainforest include hardwoods like teak, mahogany, the silk-cotton tree, and trees in the Dipterocarp family.
Other Emergent Plants
As with many forms of rainforest vegetation, the overstory possesses unique plants living in concert with the trees. Emergent plants include epiphytes, and sometimes there can be thousands on one tree, adding to its weight and biomass. Other emergent plants included lianas, sometimes numbering over 1,500 on one tree.
Intriguingly, researchers have found some interactions between overstory or emergent trees and understory trees. Ceiba speciosa especially seems to have greater species richness in its understory when compared to Senegalia polyphylla, Centrolobium tomentosum, Savia dictyocarpa, Astronium graveolens, and Esenbeckia leiocarpa. Ceiba speciosa’s uniquely rich environment might be due to producing less leaf litter or having a large crown that is attractive to animals.
Some of these stratified ecosystems are hundreds of years old. Scientists hypothesize that the emergent trees work as a filter for the trees in their surrounding canopies. More research is needed to study the influence of emergent trees on the shorter trees below them.
A Vibrant Ecosystem for Animals
The tallest trees in the emergent layer of the rainforest provide unique habitats to animals as well. Eagles perch atop them, and monkeys, bats, snakes and flying insects abound.
Predators such as eagles and other birds of prey like to nest in the tops of the huge emergent trees. They tend to raise single babies. Giant eagles can spot many kinds of prey from this high perch and swoop in dives to catch them in the canopy beneath. Central and South America’s enormous harpy eagle, at about three feet in height and with a wingspan of around six feet, represents one such species of giant eagles that excels at life in the emergent layer.
The Kapok tree also provides fibers that bird species find attractive for nesting material. Various primates and birds help disperse the seeds of these huge emergent trees, adding to the vibrancy of the ecosystem and their continued survival.
- Radford University Department of Geospatial Science: Biomes of the World: Tropical Rainforest
- Smithsonian Magazine: Researchers Discover the Tallest Known Tree in the Amazon
- Arbor Day Foundation: Layers of the Rain Forest
- Mongabay: The Overstory Layer of the Rainforest Canopy
- Acta Botanica Brasilica: Species-Specific Associations Between Overstory and Understory Tree Species in a Semideciduous Tropical Forest
About the Author
J. Dianne Dotson is a science writer with a degree in zoology/ecology and evolutionary biology. She spent nine years working in laboratory and clinical research. A lifelong writer, Dianne is also a content manager and science fiction and fantasy novelist. Dianne features science as well as writing topics on her website, jdiannedotson.com.
nature's wonderland 38. image by mdb from Fotolia.com