The Indigenous people of Canada's northern woods "do not imagine humans as separate from the land, but as part of a total system. … The water, the trees, the animals, plants, wind and rain are all spirits who share the land and with whom they must negotiate for finite resources."

Ben Rawlence learned this during a visit with members of the Anishinaabe first nation, one stop on his trip to six boreal forests around the world (Scotland, Scandinavia, Siberia, Alaska, Canada and Greenland) to research his important new book, "The Treeline."

Hopefully, most people already know how consequential trees are to the ecosystem: how they suck carbon dioxide from the air and replace it with oxygen; how leaves capture impurities in the air. But forests do much more.

For one thing, there is a complex and not yet entirely understood relationship between forest systems and world "water cycles, atmospheric circulation, carbon storage."

"Spruce forests in Alaska and northern Canada have a direct connection to the rainfall in America's breadbasket," where wheat harvests declined in both 2019 and 2020, suggesting that Native beliefs about the connective tissue linking all aspects of the natural world are something we should be paying far more attention to.

Not surprisingly, what Rawlence discovers is distressing. "The boreal forest is breaking apart." These ancient trees that are a "source of wonder," now sadly "no longer offer comfort, but warning."

Because of global warming, these important habitats now face the same threat as forests in more temperate climes.

In Siberia, for example, "the fire interval was previously five to 30 years, depending upon rainfall." Now, because weather patterns have changed, fires are an annual event. They are hotter and last longer, which makes it more difficult for trees to reestablish themselves.

Cold winters used to eliminate "even the hardiest of all insect larva, a process that kept the Arctic pristine and pest free in the summer." No longer.

Unrelated to the trees, warming is also melting the permafrost, releasing "methane, a greenhouse gas 85 times more powerful than carbon dioxide in its warming efforts."

The book is at times a bit of a slog. Rawlence occasionally repeats himself. He presupposes a level of scientific knowledge (and vocabulary) not every reader will bring.

But it is worth the effort. We're already beginning to feel the impact of climate change through droughts, food insecurity and supply chain problems. Rawlence offers no solution, but notes that understanding the danger we face and "accepting that the status quo is irretrievable is also the door to action."

Curt Schleier is a New Jersey-based book critic.

The Treeline: The Last Forest and the Future of Life on Earth

By: Ben Rawlence.

Publisher: St. Martin's Press, 304 pages, $29.99.