Related National Standards
Grade Level: 5-9
Estimated Time: One class period to watch each of the videos, though a single video will allow students to see a variety of trees. One class period to construct a broom tree and sketch the different support systems.
In this lesson, students will better understand that the environmental factors of an area affect a species's characteristics over time. The shallow, nutrient-poor nature of the soil in the Amazon basin has caused many trees to have rapid growth as they seek sunlight, and also develop interesting support strategies to hold the top-heavy trees without using taproots. By using a model, students will construct support structures similar to those used by the tall Amazon trees. Students will understand the limitations of the support structures and how environmental damage may affect the trees.
- Construct a support system that will support a top-heavy tree for one minute.
- Draw and label pictures of the three major support structures exhibited by rainforest trees.
- "Journey To Amazonia" video
- Common household brooms with rounded handle end, 1 per student group
- Duct tape
- Masking tape
- Cardboard sheets
Discuss the wide biodiversity of the rainforest areas in terms of climate, making note of the long growing seasons and high amount of moisture available. The information in the "Enter Amazonia" section of this site may help you present this information. As students watch video segments, discuss examples of competition between species as they fight over food and other resources. Relate these examples of competition to plant species growing in the jungle.
Have students describe the trees that they see in the video clips. Students should understand that the ground is relatively clear of vegetation and that wide branches in the canopy allow trees to collect sunlight to produce food.
For the broomstick exercise, divide the class into pairs or larger groups, depending on the supplies that are available. Have a materials area with rolls of duct tape, scissors, masking tape, poster board, newspaper and other materials in one part of the room. Use the items from the materials list, but include a number of other items that may or may not be used. Give each student group one broom. The object of the exercise is for the students to construct a support system that will hold the broom vertical for a period of one minute.
A fan is used at the end of the assignment to provide wind to check the trees for stability. If the trees are placed close to one another, the fall of one tree will affect those surrounding it.
The rainforest of South America covers over 2,700,000 square miles with little large-scale human development. Trees, shrubs, woody plants and vines cover the forest, though it is not like the picture most people have of a jungle. The majority of the forest is fairly clear of underbrush and easy to walk through. The bases of tall trees are seen in all directions, with the trunks disappearing into the heights of the canopy layer far above. The trees grow quickly, causing them to have very straight, narrow trunks with few lower branches. Many of the trees in the mature rainforest reach heights of 150 feet or more, which is comparable to the tall trees in most deciduous forests in the United States. However, unlike many tall trees in the forests we know, Amazon trees do not produce a deep taproot for stability.
The trees have to compete with their neighbors throughout their life. Each tall tree once started out on the forest floor in an area where a previous tall tree once stood. When that first tree fell, it brought sunlight onto the forest floor and a tangle of small plants sprouted. The current tall trees survived the tangle amd grew large enough to spread wide branches with leaves to absorb as much sunlight as possible. Over 80% of the forest's food is produced in the canopy and up to 2/3 of the animals and plants live there on the branches of the trees. The branches tend to radiate out from one area at the top of the tree, much like the ribs on an umbrella. The canopy of a tall tree may exceed 80 feet wide, making it a top-heavy monster on a thin trunk.
At one time in South America, the water in the Amazon River flowed from east to west and wore down most of the land to a broad, flat expanse. As the continental plate containing South America moved, it collided with the Nazca plate of the Pacific, which caused the Andes Mountains to form on the western part of the continent. The waters reversed and now the Amazon basin drains across the old, erosion-worn drainage basin, a distance of several thousand miles. The land that is left has few minerals and nutrients and is covered in a base of compacted clay that prevents the passage of water and the deep growth of plant roots.
Most of the roots of the tall trees can only penetrate a short distance, leaving them with little support. They have developed several unique support strategies that students will discover in this activity.
Tall trees in the Amazon basin are dependent on the other trees around them. The wide canopies at the top which touch one another keep the wind from striking the tree from the side. At the forest floor, it is rare to feel any wind at all. Thus, the support structures of individual trees have evolved to provide vertical support, not support from sideways stresses. When an area of the forest is opened due to cutting, a larger area of trees will be affected as the wind takes its toll.
The bases of the trees take on one of three distinct shapes to provide support. One group has a network of wide roots that connect to the base and run across the surface of the ground. They may run for many feet in all directions so that any sideways stresses can be distributed throughout the network. This is represented by tape that runs across the floor to the base of the broom. Another strategy is the formation of large buttresses much like those found on gothic cathedrals. The buttresses are thin extensions at the tree's base that give the tree's trunk a deeply folded appearance. Each buttress acts as a prop against stresses. Cardboard strips or other thin props alongside the broom handle represents this strategy. The last strategy is the formation of many prop-roots that come from the lower part of the trunk. Prop-roots are many small roots that surround the tree to such a density that the trunk may not be seen through them. Strings running from the broom handle to the ground represent this strategy.
- Bring in examples (or have students locate while walking around school grounds) plants with taproots versus fibrous root systems. Explain how some plants use taproots to anchor themselves firmly into the ground. Using the background information above, explain to students why plants in the rainforest can't employ this support strategy.
- To learn more about rainforest plants, especially tall trees, watch segments from the "Journey To Amazonia" videos.
- Episode Two, "Life On Land" 6:00: Treetops from the air
- Episode Two, "Life On Land" 40:00: Various views of the tall trees
- Episode Three, "The Big Top" 4:18: Shows canopy
- Divide students into groups of two (or more if you have fewer materials) and distribute one household broom to each group. Clear the center of the floor and assign an area for each group.
- Explain that each group is to construct a support system that will cause the broom to stand up by the handle for a minimum of one minute. Each student or group will explain why their solution works and problems they addressed to arrive at their solution.
- Examine the different structures and identify similarities between each group's solution. Usually, the solutions will naturally fall into the three groups that correspond to the three strategies found in the rainforest.
- Have students sketch and label the three major support structures.
- Place the trees within four feet of each other and turn on a fan in the room. Slowly direct a greater airflow at the grove of trees until one of more falls. Discuss how logging in the Amazon affects a larger number of trees than the ones actually cut.
- Using the videos (particularly Episode Three, "The Big Top"), observe the general flatness of the canopy as seen from the air. Identify the support system of trees seen throughout the video.
Students may be assessed though their participation in the construction of their tree's support system. Students may be graded on their verbal description of how their support design distributes the forces and helps the tree to stand. This description may also be done as a written assignment.
- Students may be asked to populate their tree with smaller plants and animals to represent the great number of epiphyte species that live in the branches. These organisms can be made out of clay and other materials.
- In many communities, the state Department of Agriculture or a naturalist from a park could present information on local plants and their special adaptations.
Related National Standards
This lesson addresses the following national content standards found in the McRel Standards Database at http://www.mcrel.org/standards-benchmarks/ :
- Knows that plants and animals have features that help them live in different environments
- Knows that animals and plants have a great variety of body plans and internal structures that serve specific functions for survival (e.g., digestive structures in vertebrates, invertebrates, unicellular organisms, and plants)
- Knows basic ideas related to biological evolution (e.g., diversity of species is developed through gradual processes over many generations; biological adaptations, such as changes in structure, behavior, or physiology, allow some species to enhance their reproductive success and survival in a particular environment)