MONUMENT AT 100: Tree researchers discover that old age is relative
This is the sixth in a series of weekly columns about Colorado National Monument in honor of the park’s centennial anniversary on May 24.
It’s never been a secret that most of the Utah junipers and pinyon pines at Colorado National Monument are old trees. With their gnarly, twisted gray trunks, junipers look positively ancient. (Some pinyons remind me of a wise old lady in a new green dress.)
But until recently, actual age of both species has been a mystery. Not anymore.
To answer this question (“Just how old is old?”), Deborah Kennard, a Mesa State College researcher, and a team of her environmental sciences students spent four years tediously examining 3,500 individual trees at the monument.
It was a daunting task covering two-thirds of the monument’s 20,000 acres. Her young investigators used dendrochronology, a scientific method of dating trees based on the analysis of patterns of growth rings. And they took all kinds of measurements, including girth and diameter to estimate their ages. Her office is wallpapered with yellow and brown maps that show, among other things, how a vast integrated neighborhood of senior citizens — the junipers — get along with younger whippersnappers — the pinyons.
While chopping down a few trees here and there would help to answer an investigator’s curiosity, it would result in the deaths of many old, beautiful trees. Alas, luck intervened.
Monument crews sometimes cut down trees near buildings as part of a fuel reduction program. The intent, to prevent a lightning-struck tree from burning a picnic shelter or visitor center, had the additional benefit of providing Kennard with cookies, the scientific term for sawed slabs of tree trunk.
Each cookie exposed rings. All researchers had to do was get out their magnifying glasses and start counting. Sounds simple enough except for the idiosyncrasies of the trees themselves. Unlike an oak or elm, in which a tree’s pith or first year’s ring lies near dead center of the trunk, a juniper’s pith may occur way off-center.
Imagine if the bull’s-eye were situated at a shooting target’s edge instead of its center. That would throw surrounding rings off-kilter. To confuse matters further, junipers may have as many as three, four or five trunks instead of just one.
“They are notorious for putting out false rings,” said Kennard, an associate professor of environmental science and technology at Mesa State.
The project took longer than expected, but yielded fascinating results:
The monument’s oldest pinyons are at least 350 years old — and probably much older.
The monument’s oldest junipers are at least 1,000 years — and probably much older.
No major wildfires have occurred at the monument for at least 700 years.
To put such ages in perspective, the elderly pinyons were already 100 years old when the U.S. declared its independence from England. As for the junipers, these old-timers had sprouted about the same time Norse explorer Leif Ericson became the first European to set foot in North America. That was 1003 A.D.
Kennard’s discovery that the monument hasn’t sustained large wildfires for seven centuries was a surprise.
As a fire ecologist, she expected to find “fire scars” across the monument’s landscape, similar to charred vegetation left by wildfires elsewhere in the Grand Valley. That’s because there are frequent lightning strikes every year into the highly flammable pinyon-juniper woodland. Yet no such evidence of a fire history exists.
“Which is very unusual,” she says, because fire, whether every 10 years or every 300 years, is a naturally occurring event for most forests in the West.
One wildfire broke out recently near Boulder. It was at least the third in that area since last year. Mesa Verde National Park near Durango, which has a similar climate as the monument’s, has sustained a dozen major wildfires since 1934. Those fires, all sparked by lightning, have burned 37,000 acres of pinyon-juniper woodland, nearly twice the acreage of the entire monument.
Although one or two trees may catch fire and burn every summer, they fail to ignite many of their neighbors. The most plausible reason is the absence of sufficient ground cover, particularly invasive species like cheat grass, to carry a blaze from tree to tree and across the landscape.
“That’s the nice thing about the monument,” she said. “It’s relatively pristine.”
Kennard still has to write up her study results for publication in a scientific journal, and adds, “I never would have been able to do this (project) without an army of students.”
For more information, check out this video on Kennard’s research: http://www.myfirevideos.net/Default.aspx?VideoID=414
Eric Sandstrom teaches at Mesa State College and is a seasonal park ranger at Colorado National Monument.