How Forest Bark Beetle Outbreaks Do Not Result in Larger and More Destructive Wildfires

According to a recent modeling study, bark beetle outbreaks in forests will not necessarily result in larger and more damaging wildfires-at least not for a while.

The research could someday help fire managers better decide on how to dedicate resources in fighting fires and removing fuel.

The researchers hoped that managers will be able to better assess where, when, and how to allocate resources when a beetle outbreak occurs in a forest.

Modeling Study Shows How Bark Beetle Infestations Affect Wildfires

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"There is a widespread belief in the community that bark beetle infestations will almost certainly increase fire," said Jennifer Adam, Berry Family Distinguished Professor in the Department of Civil and Environmental Engineering at Washington State University, as per Phys.org.

If you only consider the effects of climate change on fires, fire spread, or fire probability without taking into account vegetation, you will almost always get the wrong answer.

The researchers, led by Jianning Ren, a postdoctoral fellow at the University of Nevada, Reno, and Adam, published their findings in the Journal of Advances in Modeling Earth Systems.

Natural disturbances, such as wildfires, extreme weather events, and insect outbreaks are being exacerbated by climate change, and bark beetle outbreaks have recently affected millions of hectares of forest in the western United States and Canada.

The bark beetle kills trees, but it's unclear how this affects wildfires.

Some studies showed an increase in fires after beetle attacks, while others showed no increase.

That's because it's difficult to tease out the myriad of different factors affecting wildfires in the field.

Using field observations, determining when and where beetles will increase or decrease fire is nearly impossible because they don't have all the different combinations of all the different factors, according to Erin Hanan, a co-author on the paper and assistant professor at the University of Nevada, Reno.

When they're trying to understand complex interactions, Hanan used a model because they can hold everything constant and just turn one dial-like how wet it is or how much mortality we have.

Not surprisingly, the answer was extremely complex.

The researchers investigated the Trail Creek watershed in Idaho's Big Wood River basin.

They discovered that bark beetle damage may actually limit the spread of ground wildfires during the first five years or so of an outbreak.

This is due to the fact that wildfires are affected by two factors: how dry the fuel is and how much fuel there is.

The trees that have been killed by the beetles remain standing with their needles intact for the first three to five years after an attack, turning from green to a sickening red.

With a less productive forest and the normal detritus that accumulates on the forest floor, fires have less fuel to burn, and the likelihood of ground fires is reduced.

However, after a few years, the needles of the dead trees fall off, leaving a gray forest.

The fires then spread in many cases.

Another difficult-to-measure variable that influences the likelihood and extent of forest fires is how many trees die in an outbreak.

Furthermore, as trees die, the moisture level of fuels and soils changes to varying degrees, influencing fires.

Because it is a modeling study, the research cannot predict what will happen in real fires.

The models, for example, make no mention of fire suppression efforts.

Rather, the work is fundamental research aimed at disentangling the many variables influencing forest fires and assisting researchers in gaining a better understanding of the natural processes that will occur.

Also read: A Tundra Wildfire Is Advancing on an Alaska Native Settlement

Damage And Signs of infested trees by bark beetle

Bark beetles mine the inner bark (the phloem-cambial region) of tree and shrub twigs, branches, and trunks, as per UC IPM.

This activity frequently initiates a sap flow in conifers, but it can also occur in hardwoods such as elm and walnut.

The sap flow (pitch tube) is accompanied by the beetles' sawdust-like frass.

Frass accumulates in bark crevices or may fall to the ground and be visible in spider webs.

Small emergence holes in the bark indicate the presence of bark beetles.

When the bark with the emergence holes is removed, it often reveals dead and degraded inner bark as well as new adult beetles that have not yet emerged.

Bark beetles frequently attack trees that have been stressed by drought, disease, or other factors.

Although bark beetles can contribute to the decline and eventual death of trees, only a few aggressive species have been identified as the sole cause of tree mortality.

Some species of cedar and cypress bark beetles feed by mining twigs up to 6 inches back from the end of the branch, resulting in dead tips, in addition to attacking larger limbs.

Adult elm bark beetles feed on the inner bark of twigs before laying eggs, which is why these discolored shoots are commonly referred to as "flagging" or "flags."

If an adult emerges from a cut log or a section of a tree infected with Dutch elm disease, its body will be contaminated with fungal spores.

When the adult beetle feeds on twigs, the fungi that cause Dutch elm disease infect healthy elms.

Related article: Study Shows How Wildfire Triggers Major Forest Changes