Most wildfires in Canada are impossible to fight.

As smoke from forest fires in Canada have darkened skies south of the border, lawmakers in Michigan, Ohio and other U.S. states have accused the Canadian authorities of inaction and poor forest management. But most wildfires in Canada spread in such remote, vast areas that they cannot be fought effectively — and are often left to burn.

Half of Canada’s wildfires, like the ones now burning in northern Ontario, burn in such areas — either unpopulated or dotted with small Indigenous communities, said Michael Flannigan, an expert on fire management at Thompson Rivers University in British Columbia. They are most often accessible only by plane, with no roads for firefighters.

Water bombers can help from the air, Mr. Flannigan said. “They buy you time for the ground crews to put the fire out,” he said. “The boots on the ground put the fires out.”

But not only is it impossible to get firefighters on the ground in such remote areas, there is also insufficient time to react to the fires. Started mostly by lightning, they spread in the highly combustible boreal forest before firefighters can respond within the first critical 30 minutes.

Most fires are put out when they are small, Mr. Flannigan said. “But in those areas, the half-hour window passes, and the fire is up and running.”

“To be blunt, even if we spend a lot more money, I don’t think we could stop these fires,” he added.

In the long run, wildfires are also considered beneficial for forests by removing the most flammable material and by promoting regeneration. Extinguishing every fire has the effect of increasing risks, as Canadian officials have learned in managing national parks like Banff.

The areas burned by forest fires have nearly quadrupled since the 1970s, Mr. Flannigan said.

“It’s largely, not solely, due to human-caused climate change,” he said. “Warmer weather means longer fire seasons. In Canada, our fire seasons used to be fairly short, but they’re getting much longer. The warmer we get, the more lightning we see.”

Half of Canada’s wildfires are caused by lightning, he added, but they are responsible for 92 percent of the total forest surface burned — precisely in those impossible-to-reach areas.