If Trees Could Talk

Subject:
Science, Mathematics, Creative Writing, Drama

Theme:
To better understand fire, we need to broaden our perspective.

OBJECTIVE

Students will learn the cyclic nature of fire and other environmental factors affecting the growth of a tree.

METHOD

Students will study cross-sections of trees to determine the effects of fire, drought, crowding, and beetle infestation.

BACKGROUND

The only part of a tree that is actually alive is a very thin layer directly under the bark called the cambium. If a tree’s inner bark is destroyed all the way around its trunk, the tree will die. Some trees can better withstand the effects of fire than others. Douglas fir trees have thick bark, making them very resistant to fire which helps them survive. Lodgepole pine trees, with their thin bark, are very susceptible to fire. If only one side burns, they may survive but an easily recognizable fire scar will remain. If a tree survives multiple fires, this can give us an idea of the fire interval for that region. A tree’s age can be determined by counting its annual growth rings. During good growing conditions, the rings will be well spaced. In years of less favorable growing conditions, annual growth rings will be closer together.

A blue-green or gray stain on a cross-section is evidence of a fungus introduced by mountain pine beetles. As the fungi grow in the system, they prevent the free flow of water from roots to needles. This may eventually kill a tree. As with fire, beetle infestations come in cycles.

MATERIALS

Tree cross-sections with fire scars and beetle stain (check with your local Forest Service office to borrow tree cross-sections)

Tree Talk Activity Sheet

Hand lenses, rulers, pencils, yard sticks, measuring tapes

PROCEDURE

Discuss the life of trees with students. Compare the lifespan of a person to the lifespan of a tree. Ask students how they could find out what has happened during the life of someone they know who is older than they are. Ask them how they might find out about what has happened in the life of a tree? Discuss with students how they can "read" the cross-sections of trees to discover its history.

Divide students into small groups. Distribute the materials to each group and go over the Tree Talk Activity Sheet with students.

Once they have completed the activity sheet, conclude the activity with a review of everyone’s results. Discuss why differences in the results were found.

ASSESSMENT

Ask students to draw cross-sections of hypothetical trees based on narrative descriptions of their lives. For example, given the description: "I am a ten-year-old tree. I survived a fire that partially burned me when I was eight", students would draw a cross-section of ten annual rings with a fire scar at ring eight.

Here are other examples of narrative descriptions:

"I am a fifteen year old tree. I was infected by mountain pine beetles two years ago"

"I am an eight year old tree. During my lifetime I have had plenty of water and good growing conditions."

"I am a nine year old tree. Growing conditions were good for the first five years of my life. For the last four years, however, there has been an extreme drought and poor growing conditions."

EXTENSIONS

• Ask each student to write a short story describing life as if he or she were the tree.

• Find out about fires in your area and plan a field trip to explore a burned area

Tree Talk Activity Sheet (To Copy for Student Use)

Complete the questions below to discover the history of your tree.

1. By carefully counting the number of rings, you can learn the age of your tree and the time of its death. Use a hand lends to help count. How old was your tree when it died? ______________years.
   
   
2. Is the outer bark burned on your tree? If you know when this tree died, subtract your answer #1 from the year it died. Write the answer in the space below.

_________________This is the year your tree started growing.

3. Find the growth ring for the year you were born or count your age from the outside of the tree ring towards the center. Use the ruler to determine the diameter of the tree in the year of your birth.

I was born in the year ____________________ and am ___________years old.

In this year the diameter of the tree was _________inches. When the tree burned, it was

___________________inches in diameter.

4. If a tree burned partially, it may survive one of more fires in its lifetime. A fire scar looks like a dark line that extends part way around the trunk from both sides.

a. How many fires have burned your tree? ______________________

b. How old was the tree during these fires? _____________________

c. What is the average fire interval (the average number of years between two fires)?

____________________years.

5. Rings that are well spaced from one another indicate good growth years, when moisture, sunlight, and nutrients were plentiful. Periods when the rings were very close together may indicate years of drought, disease, injury, shading, or crowding by other trees.

a. Which years were the best growth years for your tree? ______________

b. During which period of this tree’s life was growth the slowest? _________________

c. Were the years immediately following the fire(s) good or poor growth years?

____________________

d. What might be a possible explanation for this?

______________________________________________

e. What is the circumference of your tree? _________________

EXTENSION

On butcher paper, draw a time line to show the lifespan of this tree and the dates of the major events that occurred in its lifetime. Use the scale of one inch per year. Include major events in human history as well.