Summit County — The link between fire risk and the pine beetle epidemic sweeping through Colorado forests may not be as conclusive as generally assumed, according to Forest Service research.
Based on a recent review of relevant studies, Forest Service scientists said there is no huge amount of evidence suggesting that insect outbreaks significantly increase the fire risk in a given area. Other factors, including the presence of ladder fuels, are equally important. However, large areas of recently dead trees still carrying red needles can result in a more intense fire and enable such a blaze to spread more rapidly.
The biggest risk to long-term forest health may come from super-hot, earth-baking fires 20 to 30 years after a bug infestation, when the trees are dead on the ground.
And even then, its important to remember that lodgepole forest ecology is marked by episodes of destruction and renewal.
None of that obviates the urgent need to mitigate obvious fire dangers to human life and property around towns and critical infrastructure, the scientists said. But all the pertinent information should be considered as land managers and residents look at the wider issue of forest health on public lands around their communities.
The life cycles of these (lodgepole) forests are punctuated by extreme events, said Dr. Mark Finney, a Montana-based Forest Service fire researcher, advocating for a nuanced and informed approach to forest health discussions and treatment options.
Running out there willy-nilly to try and solve this problem probably wont help. All this talk, all this worry that we have an emergency might just go away in a year of two on its own, Finney said, explaining that once the needles have dropped off the beetle-killed trees, they are less susceptible to a rapidly spreading crown fire than green-topped trees.
By the time a treatment is planned, reviewed and implemented, the most extreme period of immediate fire danger may already be long gone, Finney said. As a rule, human efforts to address beetle kill and fire danger are far behind the curve, he added.
The time to improve a stands health is before the bugs get in, he said. Destroying a whole stand is not a bad thing, ecologically, he said.
Obviously, when stuff is red, its more ignitable, Finney continued. But that doesnt translate into a higher probability of ignition … of a fire starting and spreading, he said.
Finney used the recent history of fires in the Black Hills of South Dakota as an example. After a series of blazes marked the area, the assumption was that a preceding beetle epidemic had contributed to the fires.
Its tempting to draw conclusions, he said. But a close comparison of fire history maps and the pattern of pine beetle infestations in that area failed to show a close geographic overlap, he explained.
Finney did acknowledge that Summit County could be facing somewhat of a worst-case scenario, with mile upon mile of trees dying within a short time. In that situation, the potential for a rapidly spreading megafire could indeed be high, at least for the one to two years when the trees are still carrying the dead, red needles high in their crowns.
At least some of the information reaching the public concerning the fire danger associated with beetle-killed trees has been muddled by generalizations and misconceptions, said Dr. Wayne Shepperd, a forest ecologist with the Forest Services Rocky Mountain Research Station.
As recently as last weeks local pine beetle task force meeting, local residents heard about the impending fire risk.
Its still looking pretty green right now. In a couple of years, it wont be so green and the fire danger will increase astronomically … most of our trees will be red. The fire danger will be extreme at that time, said Sandy Briggs, of Our Future Summit, the grassroots umbrella group for the task force.
Shepperd said Briggs is partially correct to assume that lodgepoles with red needles are more flammable. But at best, that may be an over-simplification. The reality is much more nuanced, with the fire risk depending on other significant factors, including the presence of ladder fuels, as well as wind and weather, he explained. A drought-stricken lodgepole pine forest with green trees on a hot and windy day can be just as susceptible to a big fire as a beetle-killed stand. Focusing on beetle-kill at the expense of other factors could result in a faulty rationale for decision-making, both scientists said.
Theres a popular misconception that the bugs turn the trees red and that equals more fires, Shepperd said during a recent tour of the Fraser Experimental Forest, near Winter Park. Red trees do not appreciably increase the fire risk. At least many of our scientists say no. There is no increased risk of fire ignition based simply on the fact that the trees are dead, Shepperd said.
And once the needles have fallen off, there are no longer any fine, volatile fuels to carry a crown fire through the tree canopies.
But at the same time, the needle-cast from the dead trees could make the forest floor more receptive to firebrands, said Colin Hardy, another Montana-based Forest Service fire scientist.
But with needles on the ground, theres less fire in the canopy, Hardy said. The complexity of the issue requires that resource managers be very specific about what they are trying to change, he added.
Mountain pine beetle epidemics may most significantly influence fire conditions 20 to 30 years into the future if big accumulations of large-diameter fuels on the forest floor create severe heating, consume the organic layer of the soil profile, sterilize the soil thus impeding forest regeneration, said Dave Tippets, spokesman for the Forest Service Rocky Mountain Research Station.
The message coming out of the agencys fire science lab in Montana is that the science on how insect-damaged forests affect fire behavior is still limited, but the research so far shows that those effects depend on the types of insects, the percentage of trees affected, elapsed time since the infestation and the pre-existing fuel structure.
If you have an abundance of ladder fuels and drought condition you already have hazardous fuels and a fire problem before insects kill trees, said Finney. You have to look carefully at what has been changed because of insects, and consider changes in fuel bed dynamics. Forest management activities directed at improving insect resistance to insects or removing insect-damaged trees must also address surface and ladder fuels if fire behavior is to be mitigated, Hardy said.
Resource managers and citizens also have to clearly define the terminology of the discussion, Hardy added, for example distinguishing between fire risk and fire hazard. Risk is related to the probability of a fire, while the hazard has more to do with what kind of fire it is and how it affects human values.