This lesson will give students a good understanding of how forest fires burn depending on the slope, tree density, and forest arrangement. Students will observe and record different burn patterns and use the information to analyze contemporary fires and understand more about factors influencing the spread of fire.
1. Ask the class if they know what factors cause the spread of forest fires. Write their answers on the board.
2. Tell them they will work in groups to observe how some factors contribute to the spread of fire.
3. Explain the safety issues and make sure the fire extinguishers and spray bottles filled with water are on hand for each group.
4. Divide the class into four groups and distribute the matchstick forest models.
5. Explain that each team will set up different experiments, but the whole class will observe every fire.
6. Have students insert a match in every hole of the matchstick forest model, tips pointing up.
7. Set the matchstick forests in burning trays on heat-resistant surfaces. Have the first forest be level. Attach a short bolt to the second and third forests so the slopes are about 20 degrees. To the fourth, attach the long bolt so the slope is about 40 degrees.
8. Explain that the matches represent trees that have flammable crowns. In this demonstration they will observe how slope and tree density affect fire spread through the crowns of the trees. Before lighting the matches, ask students for their guess (hypothesis) about how the fires will differ.
9. Have one team light the match tips along one edge of the flat forest and observe fire behavior. Have another team light the bottom row of matches on the medium-slope forests and observe. Have another team light the bottom row of matches on the steep slope and observe. Ask for descriptions of what they saw in terms of the Fire Triangle (heat travels upward, so matches and trees uphill from a fire receive more heat than those below and thus ignite easier). Ask students to complete the Student Worksheet, questions 1-3.
10. Have the students remove the remains of the matches from each board.
11. Explain that the tree arrangement in the matchstick forests resembles that of pine forests. Distribute the Student Worksheet, Class Page 2. This table describes the number and arrangement of trees in ponderosa pine/Douglas fir forests and white bark pine/subalpine fir forests. Ask students to set up matchstick forests resembling these two forest types – using the long bolts to make steep forests. Ask how they expect the fire behavior to differ.
12. Light these matchstick forests one at a time. Discuss observations while the students record them on the Student Worksheet, Student Page 5, lines 4 and 5. Also have them complete line 6.
13. Ask the students to compare the forests in this experiment to real forests. What are the similarities? What are the differences? How would they expect land fires to differ from matchstick fires? Explain that real land fires are much more complicated than model fires. With the models, we're dealing with only how slope, tree density, and arrangement can affect fire behavior. In a real fire, many other factors come into play: wind, the amount of fuels on the ground, fuel moisture, humidity, terrain features (canyons, draws, etc.), time of day, fire’s ability to create its own weather, etc.
This lesson is from Josephson Institute's Foundations for Life essay-writing program. For more details on this maxim-based program, visit our website:
This lesson is an adaptation of the USDA Forest Service Southwestern Region Fire Ecology Curriculum that can be accessed at http://www.fs.fed.us/r3/resources/conservation.shtml
Standard 7. Knows the physical processes that shape patterns on the Earth's surface.
Level IV Benchmark 3. Understands how physical systems are dynamic and interactive.