Using a model of succession from grasses to trees, you start out by observing a successional sequence without disturbance.

Then you get to start setting fires.

By systematically varying the size and frequency of fires, you recreate the standard textbook graph of the intermediate disturbance hypothesis showing that species diversity is highest at intermediate levels of disturbance.

In an open-ended advanced section of the lab, you can alter the susceptibility of different species to burning and their succession rate to see how these factors influence diversity.

Review:

• succession
• disturbance

---

1. Read Background in workbook. p. 1
2. Start EcoBeaker (SimBio) on computer. p. 2
3. Load 'Intermediate Disturbance Hypothesis".
4. Read species descriptions under "Species Legend".
   1. Which of the following tree species is described as having suffered population declines that have likely resulted from acid pollution?
      White Pine, Sugar Maple, Oak, Hickory
                    
   2. Which of the following is/are described as potentially invasive or weedy?
      Blackberry Bushes, American Witch-Hazel, Stickywilly
                                         
5. Run simulation without fires.
6. Stop after reaching equilibrium.
   1. Briefly describe the pattern of succession you saw over time. Did the Diversity Index change over time? How? p. 3
                                                                                                                       .
   2. What was the value of the diversity index when you stopped the simulation? Provide a brief explanation of what this value indicates.
      The D.I. was         . This indicates relatively        diversity, mostly oak and hickory?
7. SET 0.2 average fires per year.
8. RESET.
9. Run simulation until equilibrium.
   1. How do the fires influence the pattern of diversity?
                                       .

p. 4 Exercises: Run 5 simulations at different chances of spread, then 5 simulations at different fire intervals.

AVG. FIRES PER YEAR	CHANCE OF SPREAD	DIVERSITY VALUE
0.20	.01	2.01
0.20	.30	3.21
0.20	.50	3.12
0.20	.80	3.46
0.20	.95	4.77
0.01	.50	2.49
0.30	.50	7.02
0.50	.50	6.39
0.80	.50	6.29
0.95	.50	4.77

10. Run simulation for several fire sizes.
11. Record Diversity Index.
    1. Graph Diversity Index vs. Chance of Fire Spreading.
12. Run simulation for several fire intervals.
13. Record Diversity Index.
    1. Graph Diversity Index vs. Average Number of Fires per Year.
14. 3D graph or 2-line graph - SKIP.
    1. What conclusions can you draw about the role of disturbance in this system?
       Intermediate levels of disturbance (fire frequency 0.3 - 0.5) yield highest diversity.
15. TEST YOUR UNDERSTANDING
    1.