Tree rings and plant surveys: Scientists map intensity of N.W.T.'s forest fires

Dan Thompson has been tramping through burned out forest throughout the Northwest Territories this summer, looking for clues into the ecological impact of the fires that burned nearly 34,000 square kilometres last summer.

"We have good numbers about the area, from last year, and now we're trying to put together what we call a map of severity," he said.

Thompson and his colleagues with the Canadian Forest Service, a branch of Natural Resource Canada, are documenting what's growing back, what kind of damage they see, and, with help from colleagues at the Wildlife Service, the birds and other forest creatures that have come back.

"Fires burn differently," Thompson says.  "They can have a huge, variable effect on the forest ecosystem."

Fire officials described the blazes last year in almost human terms, describing the way they burned as "extreme fire behaviour."  

By documenting how that's affected the forest floor in detail, Thompson says they've learned things they could never know by simply mapping the extent of the fires from the air.

"We're not just seeing pine forest or spruce forest, we are also seeing some of the big wetlands, they're also involved in the fire.  So it's very important to look at what new trees are growing back, different vegetation that has emerged, and then it helps us plot a future of those forests."

CSI N.W.T.: Things get pretty detailed.

Thompson points to the rings of a burned branch from a pine tree, with all the enthusiasm and intensity of a crime scene investigator.  

"This one is from a little southwest of Behchoko. What is really fascinating is that it has evidence of a past fire, roughly 80 years ago.  So there is what we call a scar, from a really low intensity fire where the tree then grew around the injury."

Looking at the rings and scars, Thompson maps out a history of the pine tree, and the stand it grew in before it was killed in last summer's fires.

"We get evidence of how long ago there was a fire...we have three fires evidenced in this one tree's rings."

While Thompson is mostly interested in what's happened to the trees themselves, he says the data his crew is collecting feeds into the work of other scientists.

"We can provide information about what vegetation is there and what the habitat looks like, and that helps inform wildlife management."

"Where you had moss... you'll get berries."

Sometimes a fire wipe outs the entire canopy, from the trees down  to the shrubs, seedlings and saplings.  

The fire that killed the tree Thompson has sampled was a high-severity fire, the kind that leaves behind a devastated habitat.

"Where all the trees get knocked down, that isn't a good habitat for most things," he says.

A lower intensity fire, however, can thin out the forest floor and allow the trees that survive to grow even bigger. These thinner stands of mature trees are also less likely to burn intensely in the future.

"They can also provide really good bird habitat, ungulate habitat and all sorts of different vegetation. Where you had moss... maybe you'll get berries coming back. So that will help to inform bear habitat or caribou."

Thompson and his colleagues hope to map 50 plots around the territory this summer, each one 50 square metres.

Some of the survey areas are in Wood Buffalo, as well as near Kakisa, Fort Providence, Behchoko, and the Birch Lake fire area that sent so much smoke into Yellowknife last summer.