The Effects of Fire Exclusion in the Forest

Fire exclusion is the effort of deliberately excluding or preventing fire in an area regardless of if the fire is natural or human caused. Fire exclusion policies were in place for approximately a century. It’s important to note that fire managers were suppressing all fires because they believed they were protecting the forest. The efforts were well intentioned.

In the mixed conifer forest, a natural fire occurred every 5-15 years and tended to be a low intensity fire with occasional pockets of torching that opened the canopy. In the fire exclusion years, roughly 8 natural fire cycles were missed in the mixed conifer forest. That means that there is 8 times the amount of dead vegetation that has accumulated that can feed a fire.

Additionally, natural fires thinned the forest of some younger trees. This helped keep the forest open and, more importantly, helped the remaining trees thrive by reducing the amount of competition for water, nutrition, and sunlight.

Many of the insect and blight kills seen in forests recently in the western US are the result, in part, of overstocked forest that are weakened by increased competition and therefore more prone to infestation. 

Fires that come through the forest now are larger, more intense, and more likely to get into the canopy than in the past. This is because there are more fuels to feed the fire as well as the increased amount of trees that were not thinned through the natural fire cycle. These smaller trees can act as a ladder  and carry fire from the forest floor into the canopy.