- Hand out cross-sections from several trunks or branches (tree cookies), and have your students examine the growth rings. (If you don’t have actual tree cookies, draw a big cross-section on the board.) Ask students what they observe about the tree cookies. What causes the rings they see? What might the rings represent?
- Invite students to imagine that they are trees. What do trees need to grow? How and where do they get these resources?
- Have them draw a cross-section of themselves as trees on a piece of paper or paper plate, using growth rings to represent their age.
- Have students stand about three feet (about 1 meter) apart on their paper plates. Tell students that they’ll be playing a game called “Every Tree for Itself.” The game models how trees get what they need from the ecosystem.
- Explain that each colored square (or math cube or poker chip) represents a tree requirement: blue represents water, yellow represents sunlight, and green represents a nutrient such as nitrogen or phosphorous. The object of the game is for the “trees” to gather as many squares as they can.
- Equally distribute the colored squares on the floor around the students so the squares are about one to two feet (30–60 cm) apart.
- Give a signal to start the first round. Have student trees reach with their branches (arms) to gather their requirements. Tell students that their feet are their roots and must remain planted on their plate at all times. They are not allowed to slide their plate along the floor or step off it; they will be disqualified for doing so.
- Ask students to gather these requirements for one 30-second round. (They can either collect all types of requirements at once or one type of requirement per round.) Have students use their collected squares to create a bar graph at their feet showing the different requirements they gathered. Have students use the Every Tree for Itself Score Card student page to record how many of each requirement they gathered. Use the following questions to discuss the results of the initial round:
- How many requirements did each tree get?
- Do any trees lack a particular requirement? (Tell the student trees that they can fall down or look tired and droopy if they haven’t received their vital requirements.)
- What might happen to a real tree that lacked one of its requirements? (It might grow slowly or eventually die. Point out to the students, though, that different species of trees have different requirements.)
- Is there such a thing as too much water, sunlight, or nutrients? (Yes, every species has optimum levels beyond which the tree becomes stressed.)
- (Optional) Have students draw a “ring” on their paper plate to represent how much their tree grew that year based on the requirements they obtained. (You may have them add a ring after each round of the game. They should draw a narrow ring if their tree got one of each requirement, and a wide ring if it got two or more of each requirement that round.)
- Have students stand on their plates in groups of three to five, close enough for their shoulders to almost touch. Gather the colored squares or cubes and spread them around the room again. Play another round and have students graph and then record their results again on the student page.
- Compare the results of the second round with those of the first. In most cases, students will notice that each tree gathered fewer requirements. Ask if they can reach any conclusions about trees that grow close to each other. (Such trees compete for requirements. Often they don’t grow as well as trees that are more widely separated from one another.) Ask if any trees “died” because they couldn’t get a particular requirement.
- Ask students how foresters might use their knowledge of competition in caring for a stand of trees. (Foresters plant trees a certain distance apart so the trees will be able to get enough nutrients. The distance varies depending on the species of the tree. Foresters also thin young stands of trees.)
- Invite students to identify how they would modify the model so that all the trees in the forest get their needs met (For example, students might suggest that the colored squares be more evenly distributed throughout, that there be more of each color, or that the trees be planted further apart.)
- Have students write a conclusion from the viewpoint of the tree. What are the necessary “ingredients” for a tree to live? (Trees need sunlight, water, and nutrients, as well as space.) What are some of the reasons a tree may not get what it needs? (For example, disease, drought, or being too crowded.)
- Play the game again using the following variations. Have students first predict what will happen, and then play a round and observe the results.
- Use fewer water water squares or cubes representing a drought.
- Use fewer nutrient squares representing poor quality soil.
- Add a new color of square (red, pink, black, or brown) but don’t tell students what it represents. After playing the round, tell them the new color represents fire (red or pink), or an insect infestation (black or brown). Trees that are infected should stretch their arms out and if they can touch another tree it also becomes infected.