STRETCHING from interior Alaska across Canada to Newfoundland, and sandwiched between the prairies and the Arctic, North America’s boreal forest is a mind-boggling 1.5 billion acres in size — bigger even than the vast rain forests of the Brazilian Amazon or the Congo. And despite the relentless pace of development and industrialization worldwide, 80 percent of it remains wild and intact.

But that doesn’t mean that this region of cold-hardy trees, lakes, wetlands and tundra is safe. Corporations have their eyes on the land’s plentiful resources of minerals, timber, oil and gas, and on the hydropower potential of its many powerful, untamed rivers.

The stakes become particularly vivid at this time of year, as spring slides into summer and billions of birds — an estimated one to three billion — arrive from the tropics to spend their summers in northern Canada raising their young before returning south in the fall.

We all reap this bounty.

Almost wherever you are in the United States at this time of year, the birds of the boreal forest bridge the distant reaches of our planet and your backyard. The white-throated sparrow, until recently tuning up his lilting song at your feeder, is now in northern Quebec serenading the wolves and caribou. The Swainson’s thrush that spent the winter in northern Argentina, and that rested in the shrubbery near your mailbox after a long night of flying, is now nesting in Newfoundland.