Billions of mountain pine beetles from B.C. are expected to devastate forests in Ontario, Quebec and the Maritime provinces as they munch their way east over the next two decades, scientists predict in a new documentary.

"Most every scientist studying the beetle feels that it's inevitable," said David York, the filmmaker behind The Beetles Are Coming, which airs on CBC TV's The Nature of Things Thursday.

"It's going to happen and we're going to have to adapt."

The rice grain-sized mountain pine beetle has already wiped out an area of B.C.'s lodgepole pine forest as large as Nova Scotia and New Brunswick combined. It has since crossed the Rocky Mountains into Alberta and is heading for Saskatchewan.

The mountain pine beetle is native to northern B.C. where it has long played an important role in the renewal of lodgepole pine forests, York said.

"The beetle's job is to take out 80- to 100-year-old over-mature pine trees, thin out the canopy and allow room and nutrients for younger trees to grow."

Lodgepole pines have evolved defences against the beetles, which have also traditionally been kept in check by harsh, cold winters, limiting their damage to small outbreaks every 25 years or so.

Natural balance disrupted

York's film, based on a book Empire of the Beetle by Calgary writer Andrew Nikiforuk, explores how climate change has thrown the natural balance of the beetle-lodgepole pine relationship out of whack, and looks at the serious consequences for both humans and natural ecosystems.

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The mountain pine beetle has destroyed millions of hectares of B.C. forest, turning tree-covered mountains red and then grey. (52 Media Inc./CBC)

Warmer winters have allowed beetle populations to explode and wipe out millions of hectares of B.C. forest. The beetles have expanded their range into Alberta and jack pine forests that have no defences against this invader. The effects on forest ecosystems and the forestry industry have been devastating.

York said the story is really an illustration about the impact of climate change.

"Nobody would have expected that a simple degree and a half of warming in the interior of B.C. would unleash a beetle outbreak in 18 million hectares worth of pine forest," he said.

He added that while it's relatively easy to predict certain effects of climate change, such as drier weather that leads to droughts, "it's all of the unanticipated effects that are going to be what bite us in the ass."