Along the Way

Long the Way 700-Year-Old Douglas Firs May Hold Clues to the Future

Christopher H. Baisan's kids couldn't take one more mile cooped up in the family car, trundling up the forested slopes of 11,000-foot-high Mount Graham in southeastern Arizona. So the University of Arizona tree-ring expert pulled over, pitched camp, and by morning had stumbled onto a precious key to the ancient past. Not to mention one of those comforting Secrets of Life designed to help you through the hard times.

He owes it all to an early morning hike with the kids during which he discovered the state's oldest Douglas fir trees, a stand of gnarled, stunted survivors clinging to a cliff edge.

These hoary evergreens first set down roots more than 700 years ago, when prehistoric Indian cultures were thriving across Arizona, and Europe slumbered in the heavy grip of the Middle Ages.

And now these knotted ancients hold the key to somber puzzles of that distant past, from the movements of whole civilizations to the patterns of climate change that design the future of a thirsty Southwest. The discovery of seven live trees and several dead stumps dating back some 1,000 years has enabled scientists to add 300 years to their detailed chronology of southern Arizona. The pencil-thin cores extracted harmlessly with a hand-twisted boring tool from the living trees show by the width of their rings an exact sequence of wet and dry years.

That will enable experts to date ancient events more precisely. They can pinpoint the age of ruins from the logs used for the roof beams. They can seek the pattern in decades-long droughts to help current-day water planners. They can even check the accuracy of computer models predicting the climate change caused by the so-called pollution-spurred greenhouse warming of the planet.

The trees are growing in splintered, rocky soil on the downhill side of a ledge just off State Route 366 below Mount Graham in the upper reaches of the Pinaleno Mountains. A long sharp rock ledge protects them from the fires and diseases of the thickly forested rim.

Mount Graham, the highest peak of the Pinalenos, is what biologists call a "sky island," a lofty mountain range that rears abruptly from the desert floor. The plants and animals on its thickly forested slopes have been mostly stranded on their high-altitude island for 10,000 years, when the waning of the ice age drove the timberline upslope and biologically isolated the mountains of rugged southeastern Arizona from one another.

The oldest of the living trees first put down roots in about A.D. 1257. The oldest of the snags first sprouted in the late 900s, long before the wheel, or metal, or smallpox came to North America.

Of course these aren't the oldest living trees in the Southwest. That honor goes to bristlecone pines in California and Nevada and certain mountains in eastern Arizona. Some of the living trees are 5,000 years old, and these trees chronologies go back 8,000 years. Unfortunately bristlecone chronologies tend to be localized and hard to read because these trees stop growing when times are tough.

The tree rings may also hold the key to the future. Scientists have developed many computer models to predict what will happen if pollution doubles the amount of carbon dioxide in the atmosphere, spurring a planetwide warming. The tree rings provide detailed information about past rainfall, so that the reliability of the models can be checked by running them backward to see if they're on the mark. If the computer models can correctly "predict" the rainfall patterns of the past, scientists will have more confidence about using those models to recommend changes in activities that could cost billions to implement.

But I find the Douglas fir trees' value as metaphor more comforting than their science.

They sprout from cracks in the rock, cling to barren soil, and live on Nature's leftovers. They struggle to add a layer of wood to their outer edge that's maybe one-tenth as thick as the rings produced by the heedless striplings above them where the soil's deep and full of organic debris.

That's what it takes to grow old and wise, as can be attested by the bristlecones and other long-lived individuals.

That's what it takes to grow old and wise, as can be attested by the bristlecones and other long-lived individuals.

Something about unremitting struggle and the unceasing hoarding of resources seems to contribute to long life.

I find that comforting, now that the reckless growth of my youth has given way to the knots, swirls, and skipped growth rings of my middle years.

It's easy enough to race for the sun where the soil is deep and the rain is gentle.

I reserve my admiration these days for those rooted in rocks where the slopes are steep and moisture mostly a memory.