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Tree Core Models

Purpose

To make models of tree core samples. To describe the usefulness of these models, as well as analyze them in order to make predictions about the trees' growing conditions.

Context

Middle-school students understand that scientists collect data and analyze it using models, charts, and graphs, for example. This lesson provides students the opportunity to work with data and construct models.

In this lesson, students will make models of three tree core samples using data collected from trees that grew in the same general area of Alaska. They will analyze their models and make predictions about the trees' growing conditions, based on the size of the tree rings in the different models. This lesson encourages students to think about the usefulness of these and other models; for example, students should realize that physical models are easier to work with than what they represent because they're smaller in size, less expensive in terms of materials, or shorter in duration. (Science for All Americans, p. 168.) In addition, this lesson encourages students to recognize the importance of science and mathematics in everyday life, as well as how the two disciplines often work hand in hand.

Ideas in this lesson are also related to concepts found in the following benchmarks:

9C Mathematical World: Shapes (6-8) #6
2C Nature of Mathematics: Mathematical Inquiry (6-8) #2

Planning Ahead

Materials:

Tree Core Models student sheet
Dr. Schweingruber's data-one copy for each pair of students
plain white paper
clear tape
pencil/eraser
centimeter ruler

Read the Teachers' Materials for ACTIVITY: Tree Core Reconstruction, on the Athena Project website ahead of time.

Motivation

Have students go the Tree Rings, on the Kids Earth & Sky site. Depending on the number of available computers, students could work alone or in small groups. Have students read the text and listen to the audio.

When students are done exploring the site, ask these questions:

What is a dendrochronologist? (A scientist who studies tree rings.)
Why might scientists want to find out the age of a tree? (Answers will vary.)
How old is the tree that's depicted by the tree-ring drawing on the site? (Students will count the rings. Point out that scientists do not count the outer rings of bark when calculating the age of a tree.)
Why do you think some rings are larger than others? (The tree grew more or less that year.)
What environmental factors do you think influence the growth of a tree during a particular year? (Examples could include the amount of rain, temperature, and weather.)

Tell students that in this lesson they will create models of tree core samples. Continue the discussion by asking these questions:

Who can tell us about a model you've made?
Why was the model useful to you?
What did you use it for?
What kinds of models are useful to a scientist? (Examples could include models of the solar system, an atom, or a cell.)
Why are these models useful?
What does it mean to make a model to scale?
Why is it important to make a model to scale?

Tell students to now think about tree rings, and ask them this question:

Why would a dendrochronologist make a model of a tree core sample?

Wrap up the motivation by giving students an overview of the lesson. Tell them that they will use math and science skills to create a tree core model. They'll use data collected by Dr. Schweingruber in Alaska (1950 to 1980) from three different trees living in the same general area. Once the models are complete, they'll compare them and infer which years had good or bad growing conditions, as well as discuss what factors might have affected the trees' growth.

Development

Give each student a copy of the Tree Core Models student sheet. Then divide students into pairs and allow time for each group to make models of the tree core samples, following the instructions on the student sheet. (Average time for this activity is 30 minutes.)

When students have completed the activity, discuss the questions that students answered on their student sheets (refer to the student sheet for the list of questions).

Assessment

Use the student sheets, models, and class discussion to assess student understanding.

In addition, have students answer these questions (either aloud or in writing):

Why was a model a useful tool for examining the tree core samples? (For example, the trees grew over a 30-year time period, and did not grow in the students' backyards. The models were small and inexpensive to make. The models provided the students with a visual to use when comparing data collected by Dr. Schweingruber.)
If you did not measure accurately, would the model have been useful to you? (No, the model would not have represented the data. Accurate and precise measurements were necessary.)
Give at least two other examples of models being useful tools. (Accept all reasonable answers.)
Give at least two other examples of math skills being used in daily life. (Accept all reasonable answers.)

Extensions
The Global Change-Time and Cycles activity on the United States Geological Survey website, reinforces data and measurement skills using tree core models.

After completing the activity, students can apply what they learned by completing this task:

Examine a tree stump. Measure each tree ring in millimeters (mm) and record the data. Now convert the measurement to centimeters (cm) and create a spreadsheet or data table, using this information to create a model of the core sample. Finally, predict which years provided the best precipitation and temperatures for growth.

The Living Forest is a section of The National Arbor Day Foundation website that explains what tree rings tell us about the life of a tree.

Created :01/29/2002