Even if she didn’t have the mellifluous accent, there are moments when a conversation with Diana Beresford-Kroeger can feel like something out of Tolkien.

“I am the last of a very ancient family in Ireland. I am the last child of the kings of Munster,” she tells the Straight during a call from her home in Merrickville, Ontario. “My family castle is the castle of Ross in Killarney, we were the teachers of the high king of Ireland, and my pedigree goes back maybe 3000 years. I am a very, very important person in Ireland for that reason.”

Beresford-Kroeger is well known—though probably not well enough—as one of the more enchanting evangelists for swift and decisive action to repair the Earth’s expiring biosphere. Although trained in an array of sciences, her most acclaimed work, including the 2010 book Arboretum Borealis: A Lifeline of the Planet, emerges from her work as a botanist. She maintains a famed 60-hectare forest on the edge of her property outside of Ottawa, populated with dozens of rare and endangered tree species.

Named Carrigliath, that remarkable garden is very much on view in Call of the Forest: The Forgotten Wisdom of Trees, which follows Beresford-Kroeger from Canada to the California Redwoods and on to Japan and Ireland as she surveys the great forests of the Northern Hemisphere, engaging with other experts to present the latest scientific wisdom on the primary role played by trees in our planet’s health.

The film gets a three day run at the Cinematheque starting today (March 16), with Beresford-Kroeger herself presenting the final screening on Saturday (March 18). Following the doc's brisk and charming rundown on the remarkable healing properties of a “forest bath”, or Beresford-Kroeger’s own surpassingly simple recipe for climate change reversal, attendees shouldn’t be surprised to encounter the 72-year-old firebrand beating the drum for aboriginal knowledge, or calling for a more active synthesis of the material and the spiritual.

“I just finished a book called The Celtic Connection,” she reveals, “and I’m talking about the old Celtic world, and I’m talking about the ancient Ayurvedic and Sanskrit worlds in India, and all the ancient cultures including the aboriginal peoples of all of North America who always considered life to have a spirit, or soul, and who gave thanks to the creatures that they killed for their own food, and who were always mindful of the spiritual world around them.

"In the ancient Celtic thinking, human beings are composed of body, mind, and soul, and this was the sacred triad. There was a harmonious relationship between all three for the good working of civil society. Not organized religion; just the careful remembrance that life is just one breath away.”

She recounts her experiences with the University of California Press and Arboretum Borealis, which “was edited in such a way that they took all of the sacred thinking out of that book.” She refused to let them publish.

“I will not tolerate it,” she says. “It’s abusive to the aboriginal people, it’s abusive to the people who have succeeded in surviving on this continent, and it’s only to the aboriginal people that we can say thank you that there’s such a fantastic botanical world around us. So yeah, I have a big thing going on about the sacred and science.”

Taking on the scientific establishment and saving the Earth: one wonders how this “little old woman” (her words) maintains her energy for a project that’s “well nigh impossible” (also her words.) It turns out the answer is as old as the trees.

“When I was 11 my family was wiped out in a car crash,” she says, “and I was taken under the ancient laws—they’re called Brehon laws of Ireland—and I was taught for three years inside a Brehon wardship, before the courts decided what to do with me. And it is from that ancient culture of Ireland that I was asked to take the knowledge that I was given into the new world, because by the time I was fully grown-up, the world would need it. And that’s actually one of the foundational things behind the film that I don’t really talk about too much, but it’s the reason that I keep going, and going, and going. Now I might be a fool—I don’t know—but that’s where I come from. I want the people in the future to have a better life. I just really, really want that.”

In addition to her Q&A at the Cinematheque on Saturday (March 18), Diana Beresford-Kroeger visits Banyen Books for a presentation followed by a forest walk, on Sunday (March 19). More information here.