Distinguishing the differences between the vegetative layers of the tropics
DESCRIPTION
If you look at a cross-section of a tropical forest (although not obvious at casual glance), you will see four major vegetative layers. Within these layers animals find food, safety, and their own specialized niches. The four major layers which the students will help construct are the emergent layer, the canopy, the understory (which includes lower trees, shrubs and seedlings) and the forest floor. The conditions that exist with each layer promote difference that dictate the types of plants and animals that will live in or visit that layer. Some animals will occupy a specific layer, others will move where opportunities present themselves. By illustrating the structure of the forest, the students can begin to understand the physical changes with each section that provide areas for animals to live.
OUTCOME
The student will be able to describe a tropics ecosystem and identify some of the species the ecosystem supports.
ACTIVITY
Materials Needed
Mist bottle containing water
Tape recorder
Tape recording of tropical sounds
Umbrellas
Directions:
1. Introduce the four main vegetative layers of the tropical forest: emergent, canopy, understory (with lower trees, shrubs and seedling), and forest floor. Note: in some literature, additional layers could include lower trees and shrubs to create six layers.
2. Select students to represent each of the forest layers: as you call up each group to construct a tropical forest, either you or the students should describe the different layers of the rain forest in detail. Have one student begin as the sun, standing on a chair.
1) Emergent Layer Group: Stand on chairs with arms up in the air.
2) Canopy Students: Stand with fingers joined to form interlocking tree cover.
(Umbrellas could be used as this layer.)
3) Understory Students: Kneel with arms extended to each side.
4) Forest Floor Students: lie or sit on floor.
The Sun:
Sunlight, a key to the growth of plant life in the tropics, shines about twelve hours each day. The daily temperature remains close to 80 degrees F all year round. Tropical forests have different amounts of sunlight depending on the clouds and the amount of rainfall in a particular region of the world.
Description of the Layers:
From the ground floor, visitors to the tropical forest see large branchless trunks of trees that rise vertically all around. Plants and shrubs reveal little in the way of a layering or tiering of vegetation. Yet, many tropical forests are stratified in a way that is not obvious to the casual observer.
Emergent Layer
The emergent trees include the giant trees of the forest. The crowns of these trees may reach over 160 fee in height (as tall as a 15 story building) and spread out above the rest of the trees. They are usually the oldest trees in the forest. The emergent trees receive the most sunlight and are subjected to the highest temperatures, lowest humidity, and strongest winds. Here the eagle perches, watching for prey. Monkeys and apes leap and swing; parrots call loudly, and iridescent butterflies flash in the sun.
Canopy Layer
Located just beneath the emergent layer, tree trunks (75-90 feet above the forest floor) branch into umbrellas of trees that "rub shoulders" with each other. The canopy layer is found in most mature forests. The closely spaced trees with flat spreading crowns form a dense layer of vegetation 100 feet deep. The heavy layer of plant life blocks the rainfall. Water reaches the forest floor by rolling down branches, leaves and trunks or as a fine spray. The canopy forms the body of the tropics, shading shrubs and small saplings found below. Holes in this layer provide light gaps that encourage other plants below to grow. Rain forest plants must guard against the rain, which is everywhere. Water pooling on the leaf encourages the growth of algae or mosses, so water is quickly channeled away via the "drip tip" and hairless surfaces.
Many epiphytic plants, such as orchids, ferns and bromeliads are found in the forest canopy. In addition, vines grow on the trees forming a maze that helps tie the canopy together. The abundance of food at this level attracts a majority of insects and animals that come for the fruit, flowers and seeds.
Larger animals scamper along familiar pathways through canopy with ease. Bright birds and a vast number of smaller animals also make their homes in the canopy community. Adversity of insects hides among the leaves. In fact, most of the individual animals found in the canopy are ants.
Understory
The understory consists of vegetation between the canopy and forest floor. It is made up of smaller trees and shrubs that grow to a height of about 12 feet. This layer experiences a milder climate moderated by the large trees above. Only diffuse sunlight penetrates the canopy, less rain reaches the vegetation here; winds are greatly reduced and humidity is high/ Some trees in this layer mature at lower heights, while others do not mature until one of the taller trees in the canopy falls and creates a gap. Many animals adapted for climbing, such as the slow loris, tree kangaroos and coatis, are found in the lacework of runways in the understory.
Forest Floor
On the sheltered forest floor, the air is still, humidity is high (about 90 percent) and there is little variation in the temperature. Flecks of sunlight reach to this level. In this darkness only shade-tolerant plants can survive. Seed from trees may be dormant up to two years before germinating when a light gap may occur. A spurt of growth occurs creating fierce competition from young climbers. Antelope, frogs and ground dwelling birds may live here among termite castles and a myriad of insects and reptiles.
At the conclusion, use your mist bottle and spray water lightly on the forest layers.
3. Ask the following questions: How do the different layers adapt to the wet climate? What might happen when an emergent tree falls? Why are leaves so large in the tropics? (Maximum light - absorbing surface.) Where do some animals you are familiar with live within the layers of the tropics?
4. Identify the relationships between the producers, consumers, and decomposers in the ecosystem.
EXTENSIONS
1. Reconstruct your "forest" after learning more about the animals and place stuffed or paper mache tropical animals in the various layers.
2. Play a recording of the forest sounds as each group becomes part of the forest.
3. Students can hypothetically increase or decrease the water supply to a tropical area. Explain how plants and animals would be impacted, making clear predictions with justification.
GRADING CRITERIA
* Describe a stratified tropical forest ecosystem.
* Identify a species found in each of the four layers and describe the relationships between them.
