A new study by Christopher I. Roos of the Southern Methodist University, Dallas and Thomas W. Swetnam of the University of Arizona indicate that today’s mega forest fires of the southwestern United States are unprecedented. The study involved the analysis of 1,500 years of climate and fire patterns using tree-ring data and hundreds of years of fire-scar records gathered from Ponderosa Pine forests.
According to Dr. Roos the United States would not be experiencing massive large canopy-killing crown fires today if human activities had not begun to suppress the low severity surface fires that were so common in the past. More than a century of livestock grazing and firefighting activity has resulted in a forest structure change that includes more dense forests and subsequent fuel accumulation over the landscape. The lack of continuous fuels on the forest floor meant that surface fires ceased and the typical burn interval increasing from every 40 to 50 years to 130 years. These factors combined with climate change induced extreme drought events are more common and cause the mega wildfire events that we have witnessed over the past 15 years.
The image below demonstrates the human caused impact on a Ponderosa Pine stand on the Bitterroot National Forest in Montana over time. The stand was harvested in 1908 and has never experienced fire since 1895. The change in vertical and horizontal forest stand structure pre-supposes this forest to the mega wildfire phenomenon. In the event of a mega wildfire; and the concept of Fire Adapted Communities and the use of Firewise® principles is part of the solution to this ever increasing problem.