Many lodgepole pine forests in Montana were historically a mix of ages and tree sizes as a result of mixed-severity fires. Now the forests have trees mostly the same size and crowns touch so that when fires burn, they burn as large and severe crown fires. These fires can be dangerous and expensive to fight, leading to the loss of human and natural resources.Researchers are looking at silvicultural treatments that can minimize the probability of severe wildfires and create resilient forests.
In 2000, lodgepole pine stands in Montana were cut and prescribed-burned in two patterns: one resulted in evenly spaced trees and the second resulted in clumps of trees separated by clearcut openings. The objective was to evaluate these treatments as ways of restoring forests and managing fire behavior. The questions we asked were 1) does cutting pattern and use of prescribed fire influence fuel dynamics? And 2) are there differences in potential fire behavior due to cutting patterns and the burn treatments? In this study we tested how the treatments actually affected potential fire behavior twelve years after treatment. In 2011 they were re-measured. Because fires burn on the ground surface and in the crowns of trees, we calculated the amount of fuel on the surface and in the tree crowns. We then used statistical models to estimate the probabilities that fires would burn and spread on the surface, move (transition) into the crowns, and spread through the forest.
More trees were blown down in the evenly-spaced treatment compared to the clumped treatment.Mortality from the prescribed fires was similar in both cutting patterns.
The contribution of seedlings to fuel loads is not typically calculated but lodgepole pines grow many seedlings.We incorporated their fuel loading into our fire behavior calculations and found that sometimes they added more to the surface fuels than dead wood.
There was an overall reduction of fine surface fuels in logged stands, especially the burned units, which would reduce the spread of surface fire.
It was more likely that a surface fire would transition to the crown on treated plots, but crown fires were less likely to spread compared to the untreated plots.
Cutting and burning treatments in lodgepole pine forests can create complex structure in lodgepole forests and promote resilience to wildfire.