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## DESIGN NOTES

1. Starting # of beetles = 150
2. Students can investigate a smaller or larger forest.
3. Beetles can move up to 3 patches randomly in the forest every tick.
4. Beetles only attack trees whose size is larger than 0.5
5. The color of trees indicates the number of beetles infesting the tree.

## Module rules

1. The lifespan of a bark beetle is two hypothetical years (ticks). If it finds a proper host spruce tree, it produces two offspring and dies. If no host spruce trees are available, it dies at the age of 2.

2. Bark beetles only attack spruce trees whose size is larger than 0.5.

3. When temperature increases, fewer bark beetles die in winter (at the end of a tick).

4. As temperature increases, more bark beetles may produce one more offspring.

5. When drought becomes severer, it takes fewer beetles to kill a host spruce tree.

6. No relationships are defined between temperature and severity of drought (even it is likely in reality).

7. The ratio of spruce and other trees in a forest is set and maintained by the Tree-Diversity slider.

## Things to notice

* It is important to examine the spruce tree population when defining an outbreak.

* The y-axis upper bound automatically adjust to fit in the data. Make sure to check the y-axis bounds when interpreting data.

* The year buttons "250", "500", "750", and "1000" can be used to set a successive investigation on a certain variable with the precise time interval of 250 years.

* Bark beetle population may crash due to no available host trees in a reachable distance. It is not a programming error but a normal emergent event of the model. It will happen more or less depending on the settings you use.

## CREDITS AND REFERENCES

This module is made by Dr. Lin Xiang at Weber State University. If you mention this model in a publication, we ask that you include the citations below.

Xiang, L. (2017). Bark Beetle Epidemic. Zoology Department, Weber State University, Ogden, UT.