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Please the Trees, But Not These, Please!

Keywords: tree growth, invasive plants, tree competition; Grade Levels: third through sixth grade (ES); Total Time for Lesson: 2-hour field trip; Setting: outdoors

Objectives

Students will be able to:

  • Identify basic requirements for tree survival and indicate how these needs are met (4.6.4.A)(4.7.4.A).

  • Explain that adaptations can determine a tree's ability to compete for basic survival needs (4.7.4.B).

  • Explain that the introduction of exotic invasive species is often a human activity that has altered the environmental condition of forests (4.8.4.C).

  • Describe how changes in the forest ecosystems can affect tree growth (4.6.4.C)(4.6.4.A).

Materials Needed

Activity 1

  • "What a Tree Craves: Air, Sunlight, Food and Water"

  • "Needs of a Tree Are More Than Three" student worksheet #1

  • "What a Tree Craves" role cards, strung with loops of yarn to fit over students' heads

  • "Tree Needs" cards, 50 each, made of squares (approximately 3 inch x 3 inch) of colored paper in blue (water), green (food/minerals), white (air), and yellow (sunshine)

Activity 2: "Build a Better Tree"

Activity 3: "Too Much of a Good Thing" or "Who Invited You, Anyway?"

Activity 4: "When Disaster Strikes"

Overview

Students will learn basic parts of a tree and their functions in acquiring the survival needs of water, sunshine, food, and air. Certain characteristics of tree species may allow them to compete effectively for these limited resources, and students will learn how these relate to invasive exotic species and their effect on the growth and composition of the forest.

Procedures

Activity 1: What a Tree Craves: Air, Sunlight, Food, and Water

Background: A tree is composed of several structures that each have a specific function that enables the tree to survive:

  • Leaves: use water, sunlight, and carbon dioxide gas from the air to make food (in the form of sugar). Enough food is made by the leaves to supply the whole tree with food energy.

  • Branches: hold the leaves in place and help them to make the food.

  • Trunk: food moves through a system of "straws" or tiny pipelines in the wood from the leaves into all of the other parts of the tree. The trunk also helps the tree to stand tall, enabling the leaves to reach the sunlight they need, and stores food for the tree to use during the winter.

  • Roots: gather water and nutrients (minerals) from the soil, which the are transported up the trunk to the leaves, where they are used to make the food. The roots also hold the tree in place and store some food for winter use.

  1. Help the students to identify the requirements for tree growth such as nutrients, sunlight, water, and air. Describe for them the parts of a tree that are responsible for the functions that enable the tree to survive.

  2. Divide the students into four groups: roots, trunks, branches, and leaves. If there are an odd number of students, make the extra students leaves and branches. Give each student a "What a Tree Craves" role card to indicate the role he/she is playing.

  3. Scatter the "Tree Needs" cards onto the ground nearby. Tell the students that the different needs of trees are represented by paper squares in the following colors: blue (water), yellow (sunlight), green (food), and white (air).

  4. Explain to the students that they must each search through the cards on the ground or amongst the other players to find the needs that are listed on their role cards. For example, the roots each must find a water card and a mineral card. The trunk must find a "root" player who has already found its survival needs and escort that person to a "branch" player, who has already found a "leaf player with all its survival needs met. The lucky "trunk" will be the one who finds the extra branch/leaf, since that tree will be more able to make food for winter survival.

  5. Start the game by yelling, "Go!" In short order, all the connections should be made so that there are a number of completed trees in the forest, each having what it needs in order to survive.

Activity 2: "Build a Better Tree"

Background: The resources needed for survival by trees are in limited supply in a forest. Each tree seedling must compete with its neighbors. Sometimes it is a specific adaptation or characteristic that gives a tree species the winning edge. For example, jack pine trees have special cones that not only survive the heat of forest fires but actually use that heat to open and release their seeds. This adaptation allows jack pines to thrive where other trees perish. The Norway maple is another tree with winning adaptations: its leaves have a larger surface area; it has waxy leaves that are more resistant to drought; and it holds onto its leaves longer than many other maples.

  1. This game will be played with several successive variations. Scatter "Tree Needs" cards onto the ground nearby in the quantities described. Tell the students that the different needs of trees are represented by paper squares in the following colors: blue (water); yellow (sunlight); green (food); and white (air). Each player will pretend to be a tree, and each tree will need to gather at least one of each color of card in order to survive. Those with extra resources will grow taller and stronger and be able to produce more seedlings.

  2. The first round will represent a young forest, in which there are plenty of resources to allow each tree to survive. Scatter more than enough for each student to have one card of each color. Notice how many seconds it takes for each student to gather enough cards to survive (e.g., 18 seconds). The subsequent rounds of the game will be timed at substantially less than this amount of time (e.g., 10 seconds).

  3. The second round of the game will represent a more mature forest, in which there is competition for limited resources. Collect the "Tree Needs" cards from the trees that survived the last round. Remove about one-fourth of each color from the pack . Allow only the reduced amount of time (10 seconds as above) for the trees to gather their needs.

    What happened?
    Why were some trees unable to survive?

  4. Assemble the students who survived the competition round (the other students cheer on the survivors for now, but will soon reenter the game). Collect the "Tree Needs" cards, and again make sure that there are fewer resources than players.

  5. Now allow each surviving student to select a "Tree Species Assignment Card" from a deck of the cards (the way that "Old Maid" cards are selected). All of the students except one will represent native sugar maple trees. The one exception will be a single Norway maple.

    Explain to the group that Norway maple trees were brought to this country from northern Europe in 1762. Because it comes from a place where the winters are long and the growing season is short, it has adapted to living with less sunlight than the native sugar maples. Norway maple leaves are very large and broad, and they come out earlier in the spring and stay on the branches much longer in the fall than sugar maples.

  6. The student representing the Norway maple will be given an advantage symbolically by beginning to gather five seconds (or more) before all the sugar maples. By the end of the round, the Norway maple should have many extra resources and is assured of survival. Fewer of the sugar maples will survive.

  7. Conclude the round by reminding the students that the Norway maple's adaptations gave it an advantage that allowed it to win over the competition for resources needed for survival.

Activity 3: "Too Much of a Good Thing" (or "Who Invited You, Anyway?")

Background: When a species has such effective adaptations that it can outcompete all other species in the forest, there may be virtually no limitations to its growth and reproduction. This often occurs when a species is introduced from another part of the world--its limiting factors are no longer present. This species is called an "Exotic Invasive Species."

  1. The Norway maple is one such exotic invasive species. Unfortunately, the tree grows so easily and successfully that landscapers and nurseries have encouraged its use in American landscapes, thus unknowingly contributing to the problem. It is only within the last decade that the threat of exotic invasive species has become widely acknowledged, but the Norway maple now has a solid foothold in our forest ecosystems slowly displacing native plants such as the sugar maple.

  2. Begin this variation of the game by again selecting eight students to play the initial round. Using the "Tree Species Assignment Cards," one student will be chosen to represent the Norway maple. Seven other students will be native sugar maples. The remaining students will be "seedlings," soon to enter the game.

  3. Remind the students that the Norway maple has adaptations that give it an advantage in gathering the "Tree Needs" of sunlight, air, water, and food. In addition to a longer growing season, they have leaves so large and thick on the branches that they shade out the undergrowth. In addition, they spread a chemical into the soil near their roots that prevents competing trees from getting started.

  4. Scatter eight of each color of "Tree Needs" cards on the ground. Again, give the Norway maple a head start of 5 (or more) seconds, before the sugar maples can begin to gather their needs.

  5. When the cards are all collected, record the number of surviving sugar maples and Norway maples on a chart.

  6. Explain that each tree having survived with one of each "Tree Needs" card is able to produce two seedlings that year. Two students should join the surviving trees. Give the new "trees" a "Tree Species Assignment Card" so they will remember which species they represent. (Now there should be three Norway maples.)

  7. Count out exactly as many "Tree Needs" cards as there are trees playing the second year round. Scatter the cards and point out to the students that there are enough cards for each tree to have what it needs.

  8. However, once again the (now three) Norway maples will have a 5-second advantage. After the second year round, again count sugar maples and Norway maples. By the third or fourth round, the entire forest should be composed of Norway maples, having successfully outcompeted every other tree in the forest.

  9. Ask the students to summarize what happened during the game.

    • What happened to the sugar maples?

    • Why did the Norway maples increase in numbers so fast?

    • How many kinds of trees are now in the forest?

    • Is this a good thing or a not-so-good thing?

Confirm for the students that the forest now has just one species of tree in it. Mention to them that different kinds of forest wildlife residents need many different kinds of food sources and various places to live. How many kinds of food and shelter are present in our forest? (Just Norway maples.)

Activity 4: "When Disaster Strikes"

Background: When there is only one species of plant in an area, it is referred to as a "monoculture," i.e., the growing of a single crop. This is a common practice in agricultural production, where the land is deliberately manipulated to produce a single crop for convenience in planting and harvesting. In a natural system, monocultures are generally unstable, since a single disease or insect infestation can wipe out an entire forest (one example is the chestnut blight). Monocultures also lack the interaction between species that characterizes a healthy, sustainable ecosystem.

  1. Tell the students they are about to find out what happens when there is only one kind of tree in the forest. Everyone in the class should now be a Norway maple tree. Define the playing area by landmarks ("between that bench over there and the fence post").

  2. Now explain that a ship has arrived from Norway, bringing a shipment of Norwegian cross-country skis to deliver to Nestor's Sporting Goods. One of the skis has a small crack along the edge, and lodged in the crack is a fungus named Sporetta demapleater. The sporetta fungus is very contagious, traveling across leaf litter to attack only Norway maples.

    A cross-country skier (you) buys the dreaded skis at Nestor's. You go skiing in the midst of the beautiful Norway maple forest. The fungus hops off the skis, and when the snow melts it begins to travel across the leaf litter.

  3. At this point, tag one of the students, announcing to the group, "When you are tagged, you must tag two other Norway maple trees and then sit down on the spot because you've died."

  4. It should be only moments before the entire forest is dead from the sporetta fungus. Point out that this total destruction happened only because the Norway maple had already wiped out all other species in the forest.

  5. Extension: If desired, play this scenario out again after distributing the "Tree Species Assignment Cards" with a variety of species (including several Norway and sugar maples). Remind the students that only Norway maples can be tagged. This variation should demonstrate that a forest of diverse species composition can better withstand disaster.

Assessment

Evaluate the students' understanding of the concepts from this lesson by playing a game of "Natives and Exotics" (adapted from Joseph Cornell's Sharing Nature with Children, p. 79).

  1. Split the students into two teams, the "Natives" and the "Exotics." Have the two teams line up facing one another, several feet apart. Fifteen feet behind each team, make a "home base" line between two orange traffic cones.

  2. Make a statement out loud to the group. Use the statements listed below to begin, then add your own statements according to your own learning objectives for your students. If the statement is true, the Natives chase the Exotics, trying to tag them before they reach their home base. If the statement is false, the Exotics chase the Natives.

  3. If anyone is tagged, he or she joins the other team. If there is confusion about whether a question is true or not, discuss the answer with the group.

Sample Statements

  • A tree is an animal that lives in the forest. (f)

  • Trees need sunlight to survive. (t)

  • This is a seed from a maple tree (show them).

  • Roots enable the leaves to reach sunlight. (f)

  • A drought is a lack of rain. (t)

  • Some trees are better able to survive drought than others. (t)

  • Norway maples cannot survive in American forests. (f)

  • Exotic invasive species are a threat to native ecosystems. (t)

  • Human beings can make decisions that help the forest. (t)

  • Trees need these things to grow: water, sunlight, bubblegum, and air. (f)

References

Cornell, Joseph B. (1998). Sharing Nature with Children. Nevada City, Calif.: Dawn Publications.

Randall, John M., and Janet Marinelli, eds. (1996). Invasive Plants: Weeds of the Global Garden. Brooklyn, N.Y.: Brooklyn Botanic Gardens Publications.

Sauer, Leslie J. (1998). The Once and Future Forest: A Guide to Forest Restoration Strategies. Washington, D.C.: Island Press.

Author

Barbara Morton, Wildlands Conservancy, Emmaus, Pa.