Beetle wood adds to unpredictable nature of forest fires

Prescribed burns done in mountain pine beetle-infected wood showed the beetle wood heightens the unpredictable nature of forest fire fighting, and that beetle wood has a dramatically higher fire spread rate—almost three times that of non-beetle wood.

By Jim Stirling

t’s ironic that the warm weather which accelerated the spread of the mountain pine beetle epidemic in the British Columbia Interior should frustrate efforts to understand more of its ramifications. But that’s what happened last summer when government and industry representatives prepared a series of prescribed burns in mountain pine beetle-infected wood.

The goal was to gather empirical data on the spread rates and intensity of fire in those stands and extrapolate from that the implications of how best to respond in terms of initial attack, and suppression techniques in wildfires. However, due to weather conditions, only two of the 11 test plots were ignited.

The information gathered from those two plots is being analyzed, but seems to confirm what was previously suspected anecdotally: that fires in bug-killed wood can travel faster, canopy to canopy, than in green timber and require differently organized and delivered responses.

The test site was about 100 kilometres south of Vanderhoof and selected carefully, reports Stan Harvey, senior protection officer at the Prince George Fire Centre of the Ministry of Forests and Range. The site posed limited threat to other values, had good access, a water supply nearby and it was approved by both the Vanderhoof Forest District and Canfor, which has a logging camp in the area. Harvey notes Canfor was a partner in the project and its log contracting crews created the test plot layout.

The plots varied in size from around a half hectare to two hectares and the lodgepole pine on the plots had a mortality rate varying from 50 to 70 per cent. The two plots successfully burned were at the eastern edge of the test site (the prevailing winds are westerlies), with a clearcut area in behind them.

Harvey says the prescribed burns reinforced lessons learned fighting wildfires in BC’s beetle wood stands during the last four years. They include confirmation that the fire fuel moisture thresholds used by the ministry are reliable for beetle wood. And the faster rate of fire spread was no surprise. As a means of comparison, Harvey cites a spread rate of five metres per minute in green pine that is almost tripled to 14 metres per minute in beetle-infested wood under the same conditions.

Other characteristics emerged, like increases in the numbers of spot fires generated from red needles burning in the tree crowns and from radiation heat. “This is an important issue from a safety perspective,” he says. Modest increases in wind speed can easily create spot fires up to 500 metres away—and more of them. “It means we have to back off a bit further (when it comes to initial attack response) and use more air support than normal,” he continues.

Harvey adds that the spotting situation is compounded when the pine’s dead needles turn grey. The twigs are highly flammable and can fly “like little lighted matches.” And grey attack trees are going to dominate the Interior’s pine forests for years to come.

The beetle-killed and dying pine forests have changed initial attack strategies, says Harvey. They’ve switched to using medium-size helicopters that carry double the crews. The machines can handle large buckets for dumping water and they allow the crews to be equipped with heavier duty pumps and hoses.

The larger and better equipped initial attack crews have back-up resources to help them tackle blazes in beetle wood stands. Air tankers are dispatched provincially from Kamloops and depending upon what’s going on around the province, are typically based in high potential fire risk zones.

The other key ingredient is the forest industry. Throughout the region, licensees have a pre-organized strike force of heavy equipment to draw upon. Machines like feller bunchers, dozers and excavators are ready for dispatch to areas under wildfire attack to create fire guards, camp and supply areas and other ancillary work.

“The industry has been really cooperative,” says Harvey. “We have to do as much as we can as quickly as we can. The medium-size helicopters, the double crews and their heavier duty equipment all help lead to a quicker response time.”

Just as fire fighting strategies are altering to meet the faster rate of spread, spotting and other characteristics of beetle-infested wood, so, too, is the beetle itself evolving. Sheer beetle volumes have forced the insects to turn from their preferred hosts of mature and over-mature pine to immature stands. That has serious implications for the available cut down the road, he notes.

And it’s believed forest fires in standing trees won’t kill much more than half of the beetles within them.

“The beetles now fly right through to September, whenever there’s warm weather. Their cycles are changing.”

Put simply, the pine beetle epidemic exacerbates the unpredictable nature of forest fire fighting. “The safety side of the issue is huge,” states Harvey. Initial attack crews are often the youngest and consistent safety practice briefings are critical, he explains. “We emphasize if initial attack crews are unsure how to proceed, to get out. You need a different mind-set.” And more vigilance is required from the air to get the broader perspective of what’s happening on the ground.

“We’ve been learning lots quickly in the beetle wood stands during the last three or four years,” says Harvey. And that trend is destined to continue as the beetle epidemic runs its course.