Tree Growth

Materials Needed

• Physical model of the tree layers

  • Heartwood: cylinder or can labeled with the word "heartwood."

  • New wood: tape a piece of construction paper around the cylinder and label it "new wood/xylem."

  • Cambium: tape a piece of craft foam over the previous layer and label it "cambium."

  • Inner bark (phloem): tape another piece of construction paper over the previous layer and label it "inner bark/phloem."

  • Outer bark: wrap the model with a piece of tree bark (or attach pieces of bark mulch to resemble bark). Diagram of tree layers (enlarged from page 23 of Trees + Me=Forestry attached). Cross sections of wood for each student (or group).

• Handout of a cross section of a tree listing factors influencing growth

• Paper

• Pencil

• Glue

• Yarn

Concepts to Be Covered

• The layers of a tree: outer bark, inner bark (phloem), cambium, new wood (xylem), and heartwood

• Kinds of tree growth: height, diameter, and root growth

• Influences on tree growth including damage, shade, drought, pests, harvesting, and so on

Goals for the Lesson

• The students will identify the tree layers.

• The students will understand that a tree expands in height and diameter.

• The students will list conditions that affect tree growth.

• The students will apply their knowledge of tree growth to their own lives.

Methods: Direct Instruction-Exploration-Analysis-Application

State Standards Addressed: (4.6.A) Ecosystems and Their Interactions; Understand That Living Things Are Dependent on Nonliving Things in the Environment for Survival; Identify Environmental Variables That Affect Plant Growth

Direct Instruction

Hold up the model of the tree layers and ask the students what they think it is. Explain that it is a model of a tree and today you are going to take it apart one layer at a time to see what is really underneath.

Tell the students that before you show them the different layers, you must first explain the three ways trees grow.

• Growth takes place at the ends of the branches and stems.

• As trees get taller, they also grow in diameter to help support the tree.

• The roots also grow in length and diameter.

Tell the students as you show them the various layers that they will understand where the growth takes place. Beginning with the outer bark, identify and describe the function of each layer before removing it and proceeding with the layer beneath it (taken from Trees + Me = Forestry).

• Outer bark: the "skin" of the tree; protects the tree from injury, insects, and diseases and insulates the tree from winter cold and summer heat.

• Inner balk (phloem): contains spaces through which food travels from the leaves to the branches, stems, and roots. When the cells die, they become part of the outer bark.

• Cambium: a cell layer covering new wood; makes new bark and new wood every year.

• New wood (xylem): carries minerals from the roots.

• Heartwood: is not living wood; is where waste products from the tree collect.

Distribute the diagram of the tree layers so the students can identify the layers and notice the thickness of each.

Exploration

Distribute a cross section of a piece of wood to each student (or group). Ask the students to look at their piece of wood and try to identify the various layers. Ask the students to share other things they notice about their wood. Direct questions as necessary, asking such questions as:

• What are the rings?

• What do they mean?

• Why are they light and then dark?

• Why aren't they evenly spaced?

Distribute the handout showing a cross section of a tree listing factors influencing growth. Have students read aloud the paragraphs explaining some of the influencing factors of the tree's growth. Discuss other possible influences such as damage, drought, pests, harvesting, and so forth.

Analysis

Ask the students to look at their cross section of wood and try to determine what may have caused some of the irregularities in pattern. Allow them to share their thoughts, giving their reasons for their ideas.

Application

(Adapted from page 26 of Trees + Me = Forestry)

Explain that each student is going to illustrate his/her life by showing it in the forms of tree rings. Ask basic questions such as how many rings it will have and so on. Then ask when a person would have rings close together, far apart, and so forth.

Draw an illustration on the board, showing a sample and identifying some influences. Explain to the students that they should draw their life story and identify the influencing factors before gluing yarn on each ring.

Evaluation

Did the student indicate the age of him/herself with the appropriate number of rings? Does the ring placement reflect influences in his/her life at that time, either positively or negatively?

Reference

Hansen, Robert S. S. (1996). Trees + Me = Forestry. University Park, Pa.: The Pennsylvania State University.

Author

Hope Wenzel, Tyrone Elementary