Tree Cookies. Activity

Transcription

1 One way to learn about tree growth is to look at annual rings. Tree rings show patterns of change in the tree s life as well as changes in the area where it grows. In this activity, students will trace environ mental and historical changes using a cross section of a tree, or tree cookie. Activity 76 Levels Activity: Grades 3-8 Variation: Grades 1-3 Subject Science, Social Studies, Visual Arts, Language Arts Concepts Organisms change throughout their lifetimes. Species of organisms change over long periods of time. (5.1) While every organism goes through a lifecycle of growth, maturity, decline, and death, its role in the ecosystem also changes. (5.3) Skills Researching, Observing, Identifying Relationships and Patterns, Interpreting Information Differentiated Instruction Curricular/Personal Connections, Realia/Hands-on Learning, Oral/Reading/ Writing Skills, Prior Knowledge Links Technology Connections Internet Resources OBJECTIVES Students will examine cross-sections of trees. Students will infer from a tree s rings what environmental conditions might have occurred in its life. Students will correlate the time it takes a tree to grow with events in human history. BACKGROUND By counting a tree s growth rings, you can tell the age of that part of the tree at the time it was cut. Every growth season, a tree adds a new layer of wood to its trunk and limbs. Each ring has two parts: a wide, light part (early wood) and a narrow, dark part (late wood). The early wood grows during the wet, spring growing season. During the transition from the drier summer to fall and winter, growth slows and the late wood forms. The rings provide clues about the climate, or weather, of the area over time and evidence of disturbance to and around the tree, such as fires and floods. ASSESSMENT OPPORTUNITIES Have students look at a tree cross-section (or photograph) and write a possible scenario that accurately matches the pattern of growth rings. Read the story on page 329. Assess each drawing to make sure students have indicated the events in the tree s life at points that match the time frame given in the story. Also assess the scenarios the students create for the additional years. Many factors besides weather can affect a tree s growth. Accordingly, tree rings reflect a tree s response to such stressors as insects and disease. Sometimes a disturbance will occur after the growth season, producing a narrow or misshapen ring in the fol lowing year. To study a tree s growth rings without harming the trees, foresters or forest scientists use a technique called coring. By drilling into the center of a tree trunk with a hollow instrument called an incre - ment borer, they can remove a long, narrow cylinder of wood (called a core sample). The growth rings of the tree appear as lines on the core sample. Materials Tree cookies; copies of student pages; overhead transparency of student page, Reading Tree Cookies ; string; pins; small paper labels; paper plates; optional hand lenses; poster paper; adding machine tape Time Considerations Preparation: 15 minutes (more if cutting tree cookies) Activity: 50 minutes Related Activities Tree Factory, Trees in Trouble, Nothing Succeeds Like Succession, Every Tree for Itself, Forest Consequences, Tree Lifecycle, Adopt A Tree The shape and width of the annual rings often differ from year to year because of varying annual growth conditions. During a moist growing season, a tree in a temperate region may produce a particularly wide ring. During a drought, a colder-than-aver age winter, or an unseasonable frost, a tree will produce a particularly nar row ring. In a science called dendro chronology (which literally means the study of tree time ), scientists have found that they can learn about past climates by studying the ring pat terns of very old trees. Arizona educators use increment borer 327

2 Copyright 2015, American Forest Foundation. Permission to reprint and distribute this activity from Project Learning Tree's "PreK-8 Environmental Education Activity Guide" has been granted to Nature's Classroom. Educators can receive the complete guide by attending a Project Learning Tree workshop. Contact Nancy Peterson, Florida State PLT Coordinator, at or njp@ufl.edu. For more information about Project Learning Tree, please visit GETTING READY From the trunk or limb of a fallen tree, saw cross sections 1"-2" (3.8 cm-5 cm) thick. (Cross sections, or tree cookies, can usually be obtained from a local tree-trimming service, county or state forester, or from a utility, forest products, or firewood company.) If the wood is not dry, you will need to dry it to prevent split ting. You can do so by placing the tree cookies on foil in a kitchen oven set to warm (for five hours), putting them on a hot, sunny driveway (for five days), or laying them on a dry, well-ventilated surface under low humidity (for 10 days). Whichever method you use, turn the cookies over periodically so that both sides dry. When the cookies are dry, you may need to sand them so that the rings are clearly visible. If using an oven to dry the wood, set the temperature to the warm setting only. Higher temperatures may cause some wood species to give off fumes or to ignite. If you cannot obtain tree cookies, make photocopies of the Tree Cookie student page. Obtain an overhead projector and make an over head transparency of the student page, Reading. 328 DOING THE ACTIVITY PART A Cookie Counting 1. Pass out the tree cookies, if available, or photocopies of the Tree Cookie student page to individuals or small groups. 2. Using either the tree cookies or student page, have the students estimate how old this part of the tree was when the tree cookie was cut. Ask the students how they estimated the age. 3. Give students a copy of the student page Reading. Explain how to count the rings to find the age of a cross section (count only the light or only the dark rings). Using a transparency, count with the class the number of rings on the Tree Cookie Parts cross section. Then, using their sample tree cookies, have them count the rings to determine the age of the section they have. 4. List the following terms on the board: outer bark, phloem (FLOW-uhm) or inner bark), cambium (KAM-bee-uhm), xylem (ZEYE-luhm) (or sapwood), and heartwood. See the activity Tree Factory for a discussion of the function of each of these tree parts. Have the students label the diagram Tree Cookie Parts with these terms. Use a labeled transparency to review their responses. Next, have students identify these parts on their own tree cookies. 5. Using the Background information, explain the different kinds of markings that tree cookies display (scars from a forest fire or a dead branch, narrow rings from insect attacks or drought, etc.). Have them look for clues in the markings of the three tree cookies on the bottom of the Reading Tree Cookies student page, and guess what might have happened to the tree that time. Discuss their responses. (See the box on the next page for answers to the Reading student page.) 6. (Optional) Distribute hand lenses to the students. Have them look for small holes in the xylem and heartwood of the tree cookie. The tiny channels enable water and nutrients to travel up the trunk and branches of the tree. PART B Tree Stories 1. On a very large piece of paper, have stu dents draw a life-size cross section of a redwood tree trunk (or of a large tree native to your area). An average mature redwood is about 6 feet (1.8 m) in diameter. Draw an appropriate number of growth rings for the tree s size, about 2-4 rings per inch (2.54 cm) in diameter. Remember, there should be some variety in the growth rings to reflect changing environmental conditions. As a group, decide on the year the tree began growing and the year it was cut. 2. Divide the group into teams. Assign each team a category of research for finding information related to the tree. Categories should include (1) possible significant events in the tree s lifetime, such as years of drought, flood, or fire; (2) significant world events during the life of the tree; (3) significant events in state or national history during the life of the tree; and (4) significant events of people in your classroom, school, or community during the life of the tree. Teams should each identify at least five dates for events in their category. Have the students use the Internet, along with other resources, to obtain information for their category. 3. Have each group select a color for its event labels and make the labels. Students can staple the cross section to a bulletin board, place labels around the outside margin, and connect the labels with string to a tack inserted at the appro priate year. 4. Using three feet of adding machine tape, make a core sample for the same tree. Mark lines on the tape that correspond to the tree s rings (from the bark to the tree s center). Add the core sample to the bulletin board, and have student use string to connect the event labels to the appropriate places on the core sample.

3 Copyright 2015, American Forest Foundation. Permission to reprint and distribute this activity from Project Learning Tree's "PreK-8 Environmental Education Activity Guide" has been granted to Natures Classroom. Educators can receive the complete guide by attending a Project Learning Tree workshop. Contact Nancy Peterson, Florida State PLT Coordinator, at or njp@ufl.edu. For more information about Project Learning Tree, please visit Variation My Life as a Tree 1. Show students a tree cookie and explain how it was obtained from a tree. Let students feel and examine the tree cookie. 2. Explain what the rings on the cookie are and what they tell us about the tree (age of tree or limb, years of rapid or slow growth). Show students how to count the rings to determine the tree s (or limb s) age and let them practice. 3. Using white paper plates with ridges, demonstrate for students how to create a tree cookie using the bumpy perimeter as the bark, the smooth inside edge as the cambium, and center circle as the heartwood. 4. Have students each use a paper plate and crayons to create a tree cookie the same age as themselves. Have them identify when important events in their lives took place, such as when they were born, when they started school, and so on. They might then use this information to write an autobiography. Enrichment Invite a forester to talk with your group about how he or she uses core sampling to learn about trees and the forest environment. If possible, have the forester bring an increment borer and demonstrate its use on a tree in your schoolyard or neighborhood (get necessary permission to sample the tree beforehand). Story about Our Urban Tree (see Assessment Opportunities) Read the following story to your students and ask them to take notes. Have them pay particular attention to the years mentioned. Four years ago, there was a tree seedling planted on an urban street close to our school. In the first two years after the tree was planted there was not much rain. Since the street tree s root system was not very developed, the tree grew very slowly. Rainfall during the third year was abundant and the tree grew rapidly. In the fourth year, a car backed into the trunk of the tree, tearing off the bark and leaving some of the trunk exposed. In the fifth year, students from our school adopted the street tree, removing debris from the tree pit and watering it every week. After telling the story, allow students to ask questions so that their notes are complete. Ask them to draw a picture of what the tree s growth rings might look like. Have students create their own scenario for what happens to the tree in its sixth year, eighth year, fifteenth year, and twentieth year. Tell them that they should consider scenarios that might have positive and negative impacts on the tree s growth. Have students share the story of their tree cookie. Consider locating a street tree nearby that students can adopt. See Activity 21, Adopt a Tree, for more information. Thanks to Jessica Kratz, Greenbelt Conservancy, Staten Island NY for writing the story. Answers to Reading Student Page 1. Heartwood 2. Xylem 3. Cambium 4. Phloem 5. Outer bark 6. Dead branch (the black mark, beginning in year 13, is what remains of a branch that died and fell off. After a few years, the trunk grew over the scar.) 7. Drought or insect attack (the narrow rings signify drought, insect attack, or other growth inhibiting factors.) 8. Fire (the scarring shown here is due to a fire that came through when the tree was 12 years old.) READING CONNECTIONS Arnosky, Jim. Crinkleroot s Guide to Knowing the Trees. Simon & Schuster An illustrated introduction to trees and woodlands with information on how to identify the bark and the leaves, the many ways that animals use trees, and how to read the individual history that shapes every tree. Grades 2-7. ISBN: Hiscock, Bruce. The Big Tree. Atheneum Books MacMillan Follows the development of a large old maple tree from its growth from a seed during the American Revolution to its maturity in the late twentieth century. Grades K-4. ISBN: Johnston, Tony. Yonder. Holt Year after year, the plum tree which the farmer planted is witness to the continuing generations of his family. Grades K-3. ISBN: Markle, Sandra. Outside and Inside Trees. Simon and Schuster Discusses various parts of trees and their functions, including the bark, sapwood tubes, roots, and leaves. Grades K-3. ISBN: Vieira, Linda. The Ever-Living Tree: The Life and Times of a Coast Redwood. Walker The story plots the march of time as major events in history unfold next to the growth of an ever-living sequoia. Grades K-3. ISBN:

4 Student Page Tree Rings 330 Activity 76

5 Student Page Reading Tree Cookie Parts Cookie Clues: What happened to the tree where the arrow is? Activity