Bark beetles and fire, recent research

The Joint Fire Science Program has published a report that collects some findings from recent research about the relationship between bark beetles and wildfire. Here are some excerpts from the 1.4 MB document:

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Bark beetles are chewing a wide swath through forests across North America. Over the past few years, infestations have become epidemic in lodgepole and spruce-fir forests of the Intermountain West. The resulting extensive acreages of dead trees are alarming the public and raising concern about risk of severe fire. Researchers supported by the Joint Fire Science Program (JFSP) are examining the complicated relationship between bark beetles and wildfire, the two most influential natural disturbance agents in these forests. Are the beetles setting the stage for larger, more severe wildfires? And are fires bringing on beetle epidemics? Contrary to popular opinion, the answer to both questions seems to be “no.”

[…]

In a 2011 paper published in “Ecological Monographs” (Simard et al. 2011), Simard, Turner, and their colleagues present the startling results: a wildfire that burns in a beetle-damaged stand will probably be no more intense—that is, no more likely to develop into a crown fire—than one that burns in a green stand. In fact, the fire’s behavior in a red-stage stand may be less intense under intermediate weather conditions, because needles have already fallen from the dead trees, reducing canopy fuels significantly.

“We were surprised by this,” Turner says. The shock of seeing a red canopy may cause people to overestimate its flammability. But the modeling results showed that, while beetles and fire are linked in complicated ways, the one does not cause the other. In fact, wrote the authors, “contrary to conventional wisdom, the interaction was a negative feedback in which the probability of active crown fire appeared to be reduced.”

[…]

The few burn trials conducted in Canada have yielded no conclusive answers. Dave Schroeder of Alberta Sustainable Resource Development (wildfire operations) and Colleen Mooney of FP Innovations Wildland Fire Operations Research Group simulated a mountain pine beetle infestation by girdling jack pines at Archer Lake in northeastern Alberta in May 2007 (Schroeder and Mooney 2009). In July 2008 they burned two of the experimental stands along with control stands of green trees. In two side-by-side comparisons, crown fire developed in both the experimental stand and the control stand within seconds of each other, making it impossible to detect any significant difference in firebehavior.

[…]

When faced with uncertainty, scientific disagreement, and millions of dead trees, what’s a manager to do? “From the standpoint of active crown fire or severe fire,” says Turner, “I think what our results would say is, you certainly don’t have to go in and cut big trees. No evidence from our work suggests that salvage logging following beetles will reduce fire risk.” There may be other good reasons for taking out the wood, she says, “but if it’s justified by saying we’re going to reduce the risk of fire, I would say our data don’t support that.”

Yet some clearly have a different view. “Maybe not fire risk,” argues Battaglia, “but how about fire severity? Fire growth? Fire extent? These are just as important to consider.”

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The biggest wild card in the fire-beetle relationship is climate. “A warming climate,” says Turner, “is almost certainly why we’re seeing such a big infestation now.” Warmer temperatures bring drought, which stresses trees and makes them more susceptible to beetles, and warmer winters enable more beetle larvae to survive and breed.