Grow slowly. Heed the wisdom of long-lived trees. Heed the scientists who study the ancient trees and continue to find revelations. Heed all who would save our increasingly rare elder forests and massive trees from logging.

Earlier this fall, I interviewed Dr. Anna Sala who is a tree physiologist and professor at the University of Montana. She knows trees from the inside out and down to the cellular level. The result? Her reverence for trees merges science with the spiritual. She shared this statement with me:

“Old trees are beautiful, and their quiet resilience, humbling. Who can endure the unforgiving elements for centuries or millennia without moving? Trees can–but only the very special ones.”

Dr. Anna Sala, tree physiologist and professor at University of Montana.

There’s a special ponderosa pine in my neighborhood forest skirting the Newberry Crater lava field. I often wander the deer trails through manzanita, past the shelter snags where the Lewis’s Woodpeckers nested, and past the boulder where a coyote barked — to arrive at the lofty tree.

There, I rest my hand on the amber puzzle bark. Know this tree that has escaped the saw, the lightning strike, and disease. Know this tree is exceptional in ways I’d never considered before learning of Sala’s research.

Here’s the secret. My tree friend has always grown ponderously slow. This pine continues to bulk up — year upon year, decade upon decade, century upon century. Unlike people, trees never stop growing as they age and even at this slower growth rate, this biggest of all trees actually puts on more growth annually than the smaller trees, because of the immense circumference.

This is my big pine friend, growing strong and slow within a sliver of national forest nudging up to the extensive lava flows near the Deschutes River in Central Oregon.

Sala led research published in 2019 that revealed this startling finding about centuries-old ponderosa pines. One of the secrets to longevity is a slow growth rate that’s the result of a savvy drought survival strategy. The implication? Ponderosas that live to be older than 300 years have an edge in surviving the frequent and more intense droughts that western states are already seeing from human-caused climate change.

“The difference is in the microscopic structure of the water-conducting cells,” Sala explained. Some trees possess better safety valves to protect the transport of water from roots up to needles during the stresses of drought. The tradeoff? Safer valves make it harder for water to squeeze through, which slows down growth.

Ponderosa pines: some but not all possess the slow-growing traits that allow them to grow for more than three centuries. (photo by Anna Sala).

The discovery originated in a remote Idaho wilderness. There, Sala and UM alumnus Eric Keeling compared growth rates of 150 and 350+-year-old ponderosas. Back in the lab, Sala and UM alumna Beth Roskilly examined the trees’ xylem, the system of tubes for transporting water and minerals from roots to needles.

All the 350+ year-old trees they sampled had the superior safety valves. But among the young trees, some grew fast and some slow. Only the slow-growing ones had the specialized valves that are key to living long.

From Sala’s study on tree longevity, there might be a temptation to make a value judgement. The trees with the safer valves are surely the best. If we could find those trees and protect them, wouldn’t the future of ancient forests be as golden as the pines themselves?

Always the encouraging professor, Sala would credit me for the idea and then explain why that theory falls short. And she has the research to prove why.

In another study, she and her team turned their attention to ponderosas at the young end of the spectrum–from seedlings to 39-years- old. Examining 40 years of data facilitated by the Inland Empire Tree Improvement Cooperative, they looked at survival rates before and after a mountain pine beetle outbreak within the 4,000 planted trees.

Initially, seedlings with the fast-growth genes had the edge, with more access to sunlight and soil moisture. But as they grew older and bark beetles came raging into the stand, those seemingly vigorous trees died at higher rates from beetles than the trees with slow-growth genes.

“That’s why in natural populations there is genetic variation,” she said. “Both fast and slow growth are good, but at different times.”

What does this finding mean to forestry? The lesson lies in the significance of honoring diversity in the form of trees of all sizes, shapes, and growth rates. And her studies add to the urgency of protecting our now scarce big and old trees that store far more carbon than small trees, among many wondrous attributes. (See my blog Wildfire Wake-up: Save Carbon-storing Forests… and article in Columbia Insight: The Secret Power of Old Growth).

The other lesson? Humility. The more we know about older forests, the more we ought to respect the complexity and wisdom of our elders. Let them live long and fall when nature decides.


Note: In addition to highlighting Dr. Anna Sala’s important research, please see this new scientific paper by Dr. David Mildrexler and co-authors and the press release, where Mildrexler states: “Large trees represent a small proportion of trees in the forest, but they play an exceptionally important role in the entire forest community — the many unique functions they provide would take hundreds of years to replace.”