Are beetle-killed forests more flammable – or not?

‘Bugs and fires are neither good nor bad, they just are.’

How fire-prone are Summit County's beetle-killed forests?

By Summit Voice

SUMMIT COUNTY — Using satellites to map beetle-killed areas and forest fires in the West, a team of researchers say they are not finding much evidence that large fires occur more often or with greater severity in forest tracts with beetle damage.

The findings are in line with other recent studies that examined the relationship between beetle-kill and fires. There is strong evidence that, in some cases, beetle-killed forest swaths may actually be less likely to burn.

According to conventional wisdom, beetle-killed forests are fire disasters waiting to happen, but it may not be quite that simple — especially because some forest managers and fire officials have been hanging their hat on the pine beetle-fire danger link for quite some time. Some tend to shrug off research that runs counter to their message, which, at best, is overly simplified. At worst, it’s dangerous, because it confuses the critical safety message that trees — whether dead or alive — need to be cleared and thinned well away from homes, neighborhoods and important infrastructure in order to prevent fire damage.

“I’ve heard (the tinderbox analogy) ever since I started my professional career in the forestry and fire management business 32 years ago,” said Yellowstone National Park Vegetation Management Specialist Roy Renkin. “But having the opportunity to observe such interaction over the years in regards to the Yellowstone natural fire program, I must admit that observations never quite met with the expectation,” he said.

Since the devastating 1988 wildfires in Yellowstone, the burned areas have acted as natural fire breaks during subsequent fires. New wildfires have tended to slow and sometimes even burn out when they reach standing dead forest. There simply aren’t enough small fuels to propel the fire.

Equating dead trees with increased fire danger makes sense intuitively — the dead trees are dry and appear more flammable. Green needles on trees appear to be more lush and harder to burn, they contain high levels 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.

Those dead needles fall off the trees in a relatively short time and decompose on the forest floor. Fulfilling a natural ecosystem role, the beetles are essentially thinning the forest. The naked trees left behind are akin to large fire logs. Those logs are hard to ignite without kindling. Wildfires are less likely to ignite and carry in a forest of dead tree trunks and low needle litter, the researchers said in a press reelease explaining the research.

The recent Landsat study was a joint effort between the National Park Service and University of Wisconsin forest ecologists Monica Turner and Phil Townsend. Click here to read more at the NASA website, where you can also watch a video about the research.

First, the researchers used Landsat data to create maps of areas hardest hit by the recent beetle outbreak. The Landsat satellites capture imagery not just in the visible spectrum, but also in wavelengths invisible to the human eye. One such wavelength band combination includes the near infrared, a part of the spectrum in which healthy plants reflect a great deal of energy. By scanning the Landsat near infrared imagery, the team located areas of probable beetle damage.

Next, they hiked into the areas to confirm that the majority of the affected trees were indeed killed by beetles rather than by other causes. Mountain pine beetles leave telltale signs of their presence, including “pitch tubes” — areas of hardened resin where trees attempt to defend themselves from the boring insects by flowing sticky pitch from the wounds. By scanning the trees for pitch tubes and looking for beetle “galleries” under the bark where the adult insect lays its eggs, the team was able to confirm that they were reading the satellite imagery correctly.

Finally, the University of Wisconsin team compares maps of beetle-killed forest with maps of recent fires.

“Of course, we can’t go out and actually set a fire in beetle damaged areas where we’ve got red, green or no needles,” Townsend said. We just can’t do that, so we collect data on the ground, we collect data from satellites, and then we build models of how much fuel is there and how burnable it is.”

For Townsend, the results are a further reminder that, in complex ecosystems like that in and around Yellowstone, things aren’t always as they appear at first blush.

“I think it’s important for people not to assume that there are relationships for certain types of features on the landscape,” he says. “It’s easy to think, ‘It’s more damaged so more likely to burn.’ That’s why it’s important to ask questions and not take everything as gospel truth, but go out and see if what we think is happening in our mind is really happening on the ground.”

“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.”


5 thoughts on “Are beetle-killed forests more flammable – or not?

  1. The ideas in this piece are quite a lot for the average observer to assimilate. I hadn’t thought about the fact that, although green needles look less likely to flash in a fire than brown needles, they contain volatile oils that are more likely to fuel a fire than beetle-killed needles.

  2. Guess you could say that I am one of those that finds this research a little hard to believe from practical experience. Having been camping a great number of times over both my lifetime and the 14 years of this epidemic, I can assure you that you don’t need paper to light a fire with bone dry beetlekilled branches – simply stack a few together and light a match and whoosh, you have a campfire. Try doing that with green branches and the results are quite different. I wonder if these researchers have actually tried this themselves? Not very scientific, but it is pretty obvious that there is a difference to m ost of us. Further, as these branches fall to the forest floor, they do create tinder in which to ignite the larger branches and trees….
    Nor do they address the period of time in which trees are crashing down like pick-up sticks which creates more ground stock with which to burn hotter and higher allowing flames to reach into the dead canopies….
    Hoping they are right but a bit doubtful to me.
    Randy Piper

  3. I wonder if there is any research on the effect on forest fire of the lower oxygen at, say, 9000 – 11000 feet compared to 5000 – 8000 feet? The oxygen difference is significant.

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