Intermediate Response Hypothesis
Experimentation through diversity with fire: Boreal Forrest Biome

The intermediate response hypothesis is based upon dominance of species and how to limit that dominance through fire. Our goal was to make the forest more diverse in terms of species. In so doing we ran a simulation on the effects of forest fires. Our first experiment had us run a simulation pertaining to the chance of a fire. I ran a 50 year simulation using 10% to 100% chance of fire. I found that the most diverse percentage was at exactly 50%; the diversity jumped from about 3.5 to 7.5, these numbers pertain to the species per area. At 60% and above the diversity dropped back down to 3.5. We had a chance of spread set at 20% throughout the initial tests.

In the second simulation we ran the chance of fire at 20% then changed our chance of spread from 10% to 100%, I found that the higher the chance of spread the greater the diversity. At a 50 year interval anything below a 50% chance of spread had a diversity of about 3.5 at 50% and higher the diversity was at approximately 4.5. Fire is a key in the diversity of a forest.
In our second part we used the fire resistance phenomenon to add a bit of "realism" to the fire approach. We changed the dynamic of the forest setting by making the most dominant species, in this case hickory trees, have a chance to proliferate at the early stages of growth. We gave it a 10% chance to get established. It was enough to change the diversity by 1 from a fairly volatile environment, 50% chance of fire and spread, in our original simulation under these conditions the diversity was at approximately 4.5 but with the added chance to establish hickory trees the diversity dropped to approximately 3.5. We then added another factor: fire resistance. We set the fire resistance of the hickories at 90%. This didn't change the diversity all that much if at all. With that I hypothesized: The chance of burning should change the out come of a 100 year span to make the forest more diverse. My thinking was that there was a fundamental flaw with the outcome; essentially I did not believe the data presented. I set the resistances higher for each species: grasses 5%, other annuals 10%, blackberry bushes 30%, other shrubs 30%, white pine 50%, sugar maple 70%, Oak 90%, and Hickory 90%. I ran the simulation for a hundred year span and found that my hypothesis was wrong. It was about .2 more diverse than it was under the original simulation. So saying the program's initial set up didn't really matter either way the outcome would be the same. It would be interesting to add other pests into the forest setting such as harmful insects prone to hickory and oak. Perhaps some disease pathogens or even animal disturbance would make the species diversity even greater.
In conclusion if the diversity of a forest had only plants and fire to compete this model would be perfect. That is the nature of experimentation: limit the variables to only one to find the true impact it has on the subject. So saying to make the setting more diverse quit putting out fires!

Learn more about this author, Jack Winter.
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