Tiny tunnels bored by forest beetles could help fan wildfire flames

Long-overlooked insect architecture could cause forest fires to release more carbon

Researchers have long known that some voracious wood-eating beetles can make forest fires worse by killing trees. Now, a new study finds beetles might also fan the flames in a more subtle way: by boring tiny tunnels that increase airflow and prolong the smouldering of dead wood.

The role of beetle tunnels in wildfires had “gone sort of unnoticed until now,” says Allan Carroll, a disturbance ecologist at the University of British Columbia.

Shudong Zhang, a fire ecologist now at Peking University and colleagues at Vrije University, where Zhang did his Ph.D. work, decided to look into the boreholes with experiments involving two tree species common in European forests: the grand fir (Abies grandis) and the European spruce (Picea abies). The researchers collected 63 wood samples, each 20 centimeters long, in the Netherlands. They then used an electric drill to mimic the tunnels bored by beetle larvae. Some of the 6-millimeter-wide tubes traveled longitudinally, parallel to the wood grain; others were radial, cutting across the grain. Some samples were left without holes. After igniting the wood, the researchers documented changes including how much weight was lost and how much carbon escaped during combustion.

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The results, published last month in Ecology, showed the radial tunnels, which most closely mimicked the tunnels produced by beetles, prolonged the time the deadwood smoldered and increased the release of carbon, likely by enabling more oxygen to penetrate the wood.

The results could spell trouble for Earth’s climate. Zhang notes warmer conditions are both increasing wildfire risks and promoting beetle larvae. And more wildfires, combined with more beetles, could lead to more carbon being released during fires, Zhang says.

A new study finds beetles might also fan the flames of forest fires in a more subtle way: by boring tiny tunnels that increase airflow and prolong the smoldering of dead wood. — *Researchers have found that so-called radial tunnels bored by beetles, which open channels to the centre of a tree, can promote combustion by allowing oxygen to penetrate the wood. Shudong Zhang*

“We are learning more and more about aspects of these [wildfire] systems that we hadn’t known,” says Carroll, who thinks the study was “conducted well.”

As a next step, Zhang says he would like to study how other species that change the structure of wood, such as termites, might influence wildfires.

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