HandsOn 27 - Growing a Scattered-Seed Forest
Work in pairs. You need:
First create a random forest on a square grid, with 25 cells in the grid.
2. One student places a finger on the uppermost left square while the other student flips a coin.
3. If the coin is heads, use the green marker to make a green dot (representing a tree) on the square. If the coin is tails, leave that square blank.
4. Move the finger to the next square to the right.
5. Flip the coin. If it is heads, draw a green dot on the square; if it is tails, leave it blank.
6. Repeat this process until the coin has been flipped once for each square in the grid.
We are now ready to start a fire in our model forest, and see how far it spreads. The fire starts along the left edge of the forest and spreads from one tree to another if they are neighbors (up, down, right, left) on the grid. Here's how it works:
8. Look at each tree that is on fire. Is there an unburned tree in the next square to the right? If so, draw a red circle around it, indicating that it has caught fire.
9. Now look at each burning tree. Is there an unburned tree in any neighboring square (up, down, right, left) ? If so, draw a red circle around it. This is how the fire spreads. (We are assuming that fire does not spread directly between two trees that are diagonally next to one another.)
10. Continue to "spread'' the fire from each burning tree to any unburned tree in a neighboring square (up, down, right, left) until it can go no further, so that there is no unburned tree left next to a burning tree.
Grow a new forest on the same size grid, but this time roll a die for each square, placing a tree if the die comes up 1, 2, 3 or 4 and leaving the square blank if the die shows 5 or 6. Now predict what you expect to happen when you start a fire along the left edge. Will more or fewer fires burn across to the right side of the forest than before? Try it!
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