It is climate change, not the mountain pine beetle, we should be worried about.
Researchers have found that forests infested by the mountain pine beetle (Dendroctonus ponderosae), which is present in thousands of miles of forest in western North America from Mexico to British Columbia, has no added effect on the risk of wildfires compared to forests unaffected by the insect. Instead, it is more important for policy makers to address the bigger causes of forest fires, the researchers say.
"The bottom line is that forests infested by the mountain pine beetle are not more likely to burn at a regional scale," says Sarah Hart, postdoctoral researcher at the Colorado University-Boulder and lead researcher. "We found that alterations in the forest infested by the mountain pine beetle are not as important in fires as overriding drivers like climate and topography."
The small, black bark beetle is known as a tree-killing specie. In recent years, populations of the mountain pine beetle have survived the increasingly warmer winters, allowing them to kill more trees. With more dead dry trees, which contain only 10 percent of the moisture of healthy trees, it is logical to conclude that wildfires will spark more quickly with the presence of more fuel, a conclusion that has guided local wildfire prevention and response policies in the last few years and confirmed by small-scale studies conducted by the U.S. Forest Service.
But the researchers say the big picture shows something different. Using data from the Forest Service and the U.S. Geological Survey, the researchers created maps of wildfire burns and beetle infestation 11 states, which comprise 46 percent of the total area burned in the West from 2002 to 2013. They chose data specifically from 2006, 2007, and 2013, which constitute the peak burn years during the study's period. Superimposing these maps, they found out that beetle infestation is not much more of a problem causing wildfires than drought.
"What we are seeing in this study is that at broad scales, fire does not necessarily follow mountain pine beetles," says study co-author Tania Schoennagel. "It's well known, however, that fire does follow drought."
The study, which is the first peer-reviewed, large-scale study to monitor the effects of the mountain pine beetle on forest fires. The researchers believe their findings could help the government better allocate funds to forest conservation. In 2014, the Farm Bill allocated $200 million to reduce insect outbreaks and wildfire risks in some 70,000 square miles of forest in the National Forest.
"We believe the government needs to be smart about how these funds are spent based on what the science is telling us," says Schoennagel. "If the money is spent on increasing the safety of firefighters, for example, or protecting homes at risk of burning from forest fires, we think that makes sense."
The researchers acknowledge that mountain pine beetles may affect forest fires in other ways, a statement voiced out by Forest Service researcher Matt Jolly, who says beetle-killed trees are more vulnerable to igniting from sparks or burning branches carried by the wind or a heat wave.
"How that fire is burning is the most important thing," Jolly says.
The study is published in the Proceedings of the National Academy of Sciences journal.