Tree Cookies

Overview

Students will measure and analyze features of two different species of trees by using their cross-sections (cookies). Further analyses will allow students to graph their results and apply the knowledge gained to an understanding of tree growth, health and diversity.

Objectives

• Students will use and understand the following terms: radius, diameter, circumference and area of a circle.
• Students will calculate area and circumference (to check their circumference measurements).
• Students will make quality graphs, make predictions based on their data, and practice critical thinking skills.
• Students will communicate their findings and reasoning to a small group of students.

Lesson Preparation

Background Information:

Dendrochronology is the dating and study of annual tree rings. Dendrochronologists are scientists who use tree rings to answer questions about the natural world and the place of humans in this world. Tree rings can tell us many things, such as past and current environmental processes and conditions as well as help us understand possible future issues.

Two of the main kinds of trees are found in Interior Alaska: Alaska paper birch and white spruce. One way to study the health of trees is to look at tree cookies, cross sections of trees that can give a lot of information about the tree’s growth history and health, such as age and growth conditions (water availability, temperature, pest populations, fire).

Procedure

Activity 1

Hand out 4 birch tree rings to each group of students. Tell students not to count the rings just yet. Ask students what tree rings can tell us and have them jot a list down on a piece of paper. Do a Continuous All Write Round Robin: Students share ideas around the group and everyone writes down the ideas if they have not already listed them on the paper. Share as a class and the teacher makes a list so that class can view. It is likely students will know that they can count the rings to find the age. Have students estimate the rings on each tree cookie in their group…do they all come up with similar estimations? Now students count the rings. Do the all come up with exact same answers? Do another All Write Round Robin answering, "Why do you think you came up with different answers?" Discuss as a class.

Activity 2

Show PowerPoint or have guest speak introducing tree rings, what they can tell us and maybe look at a couple of different methods to count them (I’m currently trying to see if I can get a guest speaker from the Laboratory of Tree Ring Research located at the University of Arizona to do this!).

Activity 3

Bring out the rest of the tree rings—these should be the White Spruce rings. Ask students to look and, doing an All Write Round Robin, list the differences between the two different kinds of tree cookies. Share as a class. Give students the handout and instruct students that they will be doing a small investigation to discover if it is possible to tell the age of a tree by its circumference. Students will be doing numerous measurements, then calculating circumference. Once all measurements are taken, students will use them to make graphs. Groups may work together, but each individual makes their own graphs.

Activity 4

Each student in the group needs to have their graphs completed. Have each student present and explain one of their graphs to the group. Then students decide on the best way to graph the final version as a team. Hand each group 2 large pieces of graph paper. The final version of their graphs goes on this paper, which is to be glued on a large piece of butcher paper. A table and one calculation should accompany each graph on the paper to show the data that is graphed. Have students hang graphs up at the time limit. Then do a gallery walk, where students go to each graph as a team and discuss. Possible questions to pose to the teams:

• What makes a good graph? A great graph?
• Do all teams have the same answer?
• Are example calculations accurate, thorough and easy to read?
• What could you do to make your calculations/proof more effective?
• Are all graphs the same? If not, what are the differences in the graphs?
• After looking at other graphs, what could you do to make your graph even better?
• Did other groups come up with the same conclusions?

Activity 5 (optional)

Have students repeat Activities 2-4, except using the other set of tree rings they didn’t originally work with and investigating relationships via the area of the tree cookie’s surface.

Extension

• Writing Connections: Compare and contrast the two sets of tree rings. What may cause the differences you notice?
• Science: What are the parts of a tree ring? Explain the purpose of each part of the tree ring. What do you think the tree cookies of Alder would look like? Why?
• Art: Make sketches of the bark of different trees. Give short descriptions of each bark. Predict why each bark is the way it is…is it thick, thin? Why? Then research your question to check your answer. Were you correct? If not, what is the actual reason for the type of bark?

Resources

• http://www.idahoforests.org/cookie1.htm
• http://www.treetures.com/RingALing/RingTeacher.html
• http://ltrr.arizona.edu/

Credits

Sunny Castleberry sunny.castleberry [at] k12northstar.org
This lesson was created in as a result of a teacher training in climate change through the Murie Science and Learning Center in Denali, Alaska.