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The mechanism controlling the interaction between Populus remuloides (aspen) and Abies laslocarpa (fir) is that of a facilitation relationship. Figure 3 shows that when there is less aspen, fir die significantly more.  One reason may be due to fir being able to take over the stands much faster than they would be able to in the normal successional cycle. If fir are taking over faster, and more often then the case of fires is going to occur more. With more fires the cycle will begin again after both species get burnt down. Aspen will then arrive first, and if re-thinned will get taken over by fir again very quickly resulting in more frequent fires and a higher mortality rate for fir. The Aspen morality rate does not increase by a lot because by the time the fire occurs the plot is already overtaken by fir.