Modeling Forest Fires using Probability Modeling Tools to compare Forest Management practices of today versus Forest Management practices of the Past.

by Abram Cushner WS Peirce MS Philadelphia

Objectives:

In this lesson I plan on having the students experience modeling using probability modeling tools (cellular automata). They will learn what a model is, what probability modeling is and how probability modeling truly models real life events. Using this tool the students will compare and contrast Forest Management techniques of today; controlled burning of federal park lands yearly versus the Forest management of the middle part of this century in which forest fires of any sort were put out as quickly as possible.

Materials:

National Park Service Teacher Fire Ecology
A Copy of StarLogo
A set of satellite pictures of forest fire scars
For each group:
1 (3) Blank cellular automata wk sheets
2 (2) Colored pencils of different colors
3 (1) Random number generator from 1-10
10 sided dice found at any hobby/game shop
or a calculator that has a random number generator
or a bag with the numbers in them
or a spinner with 1 to 10 on it etc.

Background Cellular Automata Wk Sheet

This activity simulates the spread of a forest fire as an interacting particle system. What this means is you will create a grid of blocks like graph paper but with smaller blocks. Shrink a piece of graph paper to 25% and put 4 of these together so it agains a single 8 by 11 sheet. You will fill a block of 3 by 3 in the center of the paper. Every where two blocks touch on a flat side NOT ALONG THE DIAGONAL you will see if it catches fire if it does fill that block with the brighter of the two colored pencils you have, if it does not leave it alone. Once all neighboors have been checked to see if they catch fire, fill the original block the darker of the two colors. Continue this process until all of the first generation blocks have had their neighbors checked. That was iteration number one. Now start iteration number two continue until fire burns out.

How you decide if a cell catches is do to your random number generator. Lets say the probability that any tree will catch fire is 50%, that means if your random number generator creates a number 1-5 the tree burns, if it creates a number from 6-0 it does not. Remember if an un burned tree is touched by two burning trees along flat sides you must test twice.
The Model is done when in the last iteration nothing caught fire.

Procedure:

1. Explain the idea of modeling using the modeling forest fire work sheet.
a. demonstrate the technique using an overhead projector and model the correct method by running through a couple iterations for the students at 50% possibility of fire jump.
b. Let the student create their own models while you guide their progress. Do these models you have created really show how a forest fire behaves, why or why not? Try to come to a consensus either way.
c. Now show the students the series of satellite pictures and compare these images to the models created by the students. How do these images compare with the model you created? If possible the class should come to the understanding that the models are similar if not perfect reproductions.

2. Discuss what the students would do if a forest fire breaks out in a national park? Major understanding is that if a fire breaks out you should put it out immediately. How do you think this affects the forest? Discuss build up of dead pine needles, dead wood, older trees, high canopies with dead dry debris covered forest floor. How do you think this will affect the probability of fire jump from one cell on the model to another? Hopefully the students will understand that this will increase the chance, meaning raise the probability.
a. Now pass out the first blank modeling sheet. Explain to the students no fire has burned in this forest for years and for each year the probability of fire jump goes up one percent. It is at least 10 years since that last fire, then randomly pick each group to be 61%, 62%, 63%, etc. up to 70%. Then a fire starts and there is no way to put it out, maybe no water, no man power etc.. The only way for it to go out is if it burns it's self out.
b. Let the student create their own models while you guide their progress.
c. How were these fires different from the original models you created? How are the models that each individual group created different from each other? Try to come to a consensus that these fires burned more completely and covered much more area than the original fire. Also the class should look at how the higher probability makes the fire last longer and how the area affected becomes much larger. Is this a good way to manage a forest, why or why not?

3. Now a discussion needs to be started on forest management used today, and how fires are started in a control way to clean up the forest floor. This allows ground cover to form, green growing stuff. Allows younger trees to grow and removes a large portion of fuel that a fire would burn to be removes. How do you think this will affect the probability of fire jump from one cell on the model to another?
a. Now pass out the second blank modeling sheet. Explained to the students that this forest has been under present day management for many years. Controlled burning have occurred, old dead trees have been removed and the forest is a health growing environment. Explain to the students that the probability is now some where between 30% and 40% for fire jump between cells. Randomly assign percentages to each group. Then a fire starts and there is no way to put it out, maybe no water, no man power etc.. The only way for it to go out is if it burns it's self out.
b. Let the student create their own models while you guide their progress.
c. How were these fires different from the original models you created? How were these fires different from the second models you created? How are the models that each individual group created different from each other? Try to come to a consensus that these fires burned out much quicker that less area was effected and the forest was able to take care of it's self as in a natural ecosystem. Is this a good way to manage a forest, why or why not?

4. Now if possible move the class to a computer lab and show the students the modeling program Starlog. explain to them that computers can be used to do what you did with paper and pencil. Let them play with the different setting for 10 to 15 mins.

Final assignment:

Have the students as teams create a comparative set of images at different probabilities having them explain what they think is happening in each image.
or
For more advanced students have them do research on Forest Fires of the past and have them match up these probability models with actual fires.

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