Firefighters should calm down about beetle-killed forests

pine beetle damageThe dirty little secret that some firefighters and land managers either don’t know or will not admit to knowing, is that forests that have been affected by mountain pine beetles are less likely to burn as intensely as green forests. When the needles on a pine tree die, the volatile oils that cause a green, healthy pine tree to torch and support a crown fire, break down. And a tree with no needles is not a good candidate for a crown fire either — less so than a green tree.

Sometimes land managers, when faced with a landscape of brown, ugly, beetle-killed trees, fall all over themselves finding additional taxpayer funds to “fix” the problem, such as a state Governor vowing to order his state employees to storm into a federal wilderness if there are any fires in the area, which has some beetle-killed trees, or a 1,200-acre park asking for $5.7 million to fix a possible future beetle problem.

Some scientists have tried to say that the wildfire potential in areas affected by beetles is over-stated. But now there is new research that further confirms that point of view. And it appeared on the NASA web site, whose satellites were used to collect some of the data.

University of Wisconsin forest ecologists Monica Turner and Phil Townsend, in collaboration with Yellowstone National Park Vegetation Management Specialist Roy Renkin, are studying the connection in the forests near Yellowstone National Park. Roy, by the way, is also a qualified Fire Behavior Analyst, who I have worked with many times on fires. He knows his stuff.

Here is an excerpt from the NASA article:

Their preliminary analysis indicates that large fires do not appear to occur more often or with greater severity in forest tracts with beetle damage. In fact, in some cases, beetle-killed forest swaths may actually be less likely to burn. What they’re discovering is in line with previous research on the subject.

The results may seem at first counterintuitive, but make sense when considered more carefully. First, while green needles on trees appear to be more lush and harder to burn, they contain high levels of very flammable volatile oils. When the needles die, those flammable oils begin to break down. As a result, depending on the weather conditions, dead needles may not be more likely to catch and sustain a fire than live needles.

Second, when beetles kill a lodgepole pine tree, the needles begin to fall off and decompose on the forest floor relatively quickly. In a sense, the beetles are thinning the forest, and the naked trees left behind are essentially akin to large fire logs. However, just as you can’t start a fire in a fireplace with just large logs and no kindling, wildfires are less likely to ignite and carry in a forest of dead tree trunks and low needle litter.

[…]

“Both fire and beetle damage are natural parts of system and have been since forests developed,” Townsend said. “What we have right now is a widespread attack that we haven’t seen before, but it is a natural part of the system.”

Renkin agrees with the assessment. “Disturbances like insect outbreaks and fire are recognized to be integral to the health of the forests,” he said, “and it has taken ecologists most of this century to realize as much. Yet when these disturbances occur, our emotional psyche leads us to say the forests are ‘unhealthy.’ Bugs and fires are neither good nor bad, they just are.”

What this boils down to is that the rate of spread and flame lengths of a fire in beetle-killed lodgepole pines will be less than you would see in green stands of lodgepoles. But fighting fire in an area that has a large number of dead trees can be extremely hazardous for firefighters due to the snags falling as they burn. Green trees are less likely to burn through and fall in the first few hours or days after a flame front moves through. Too many firefighters have been killed or injured by falling snags, or while cutting down snags.

Author: Bill Gabbert

After working full time in wildland fire for 33 years, Bill Gabbert now writes about it from the Black Hills. Google+