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Tree-Ring Research in Sequoia National Park is Hard Work with Important Payoffs


Researchers at Sequoia National Park count tree rings on a sequoia cross section. NPS photo by Tony Caprio.

Tree ring data obtained from 52 ancient trees in Sequoia National Park has provided scientists with 3,000 years of record. It didn’t come easy, though. Working with the immense trees required special equipment, ingenuity, and heavy labor.

Scientists routinely employ dendrochronology – the study of tree rings -- to get vital information about droughts, fires, and other patterns and incidents that happened long ago. Trees that are hundreds of years old are especially valuable storehouses of such information.

In the case of Sequoia National Park, where researchers obtained tree ring data from the park’s Giant Forest area to study droughts, fires, and other incidents and patterns of the very distant past, the living trees are up to 2,700 years old. While this research allowed scientists to add a thousand years worth of data to the extant tree ring record for the park, obtaining the tree ring information did pose special problems.

The boring tools used to obtain the long, pencil-thin cores normally used for lab analysis have a maximum length of around three feet. While that’s plenty enough for typical uses, the park’s Giant Forest sequoias are as much as 32 feet in diameter (about 16 feet from bark to center). The researchers needed a plan B, so they asked for and got permission to use cross-sections of downed logs and standing dead trees (snags).

The size and weight of the more than four dozen huge samples that had to be cut and hauled out for study posed unusually difficult logistical problems. Added to this was the need to hold disturbances of the Giant Forest to a practical minimum. Small wonder that the job not only required many workers, but also had to be spread out over many field seasons.

The workers cutting the samples used chain saws with seven-foot bars, the largest researchers could obtain. Once cut, the giant slabs, each weighing several hundred pounds, had to be transported to the road -- which in some cases lay over a mile away. Wheeled litters like EMTs use were employed for this job, and you have to admire the strength and endurance of the work crews that pulled it off. Just thinking about the labor involved is enough to wilt the resolve of all but the most determined individuals.

This complicated multidisciplinary research project was conducted by teams of scientists from Arizona, California, Colorado, and Alberta, Canada. Funding and other support was provided by the National Park Service, the U.S. Geological Survey, Mountain Home Demonstration State Forest, and Calaveras Big Trees State Park.

The scientists who studied the tree ring data have learned (or confirmed) important facts about the climate and fire history of Sequoia’s Giant Forest area. There is intense interest in evidence of fire events that occurred in the Giant Forest during the Medieval Warm Period, a five-century long (800-1300) warm spell when droughts were unusually severe and fires happened more often. As the climate of the modern era warms, it may produce conditions like that long-ago period.

Thanks to this and related studies, scientists have ever-stronger empirical evidence that frequent low-intensity fires are needed to maintain the health of sequoia forests. As the modern climate grows warmer, the very survival of the giant sequoias in Sequoia and Kings Canyon National Parks may hinge on a fire management program that introduces low-intensity fires at intervals akin to those of the Medieval Warm Period.

The salient findings of the study have been reported in an article entitled "Multi-Millennial Fire History of the Giant Forest, Sequoia National Park, California, USA" that was recently published in the electronic journal Fire Ecology. For more information, visit this site.

Postscript: Scientists trying to nail down their understanding of nature’s workings like to have corroborating evidence obtained from independent studies using different methodologies. In the case of the sequoia fire record, that corroborating evidence is provided through the study of charcoal deposits in meadows mixed in with the sequoia groves. It turns out that these charcoal deposits -- sampled via sediment cores, and dating as far back as 8,000 years -- correlate closely with the tree ring data. The charcoal specialists, we might reasonably suppose, would rather have us say that the tree ring studies back up their own findings


With 3000 years the Sequioa tree ring calendar is the longest fire history calendar, but by far not the longest tree ring calendar as such:

The longest right now is composed by the University of Hohenheim in southern Germany. It reaches back about 14600 years, but unfortunately it is not properly published. This calendar is composed by "wiggle matching" tree rings of oak trees found in swamps and marshes. The bristlecone calendar from California and Nevada reaches back some 9000 years.

Thanks for clarification, MRC, and the good catch. I revised the article to delete the inaccurate statement you pointed to. Bye the bye, I thought that the longest fire history calendar extant is based on the analysis of charcoal deposits, not tree rings. And about that bristlecone calendar. Didn't some guy illegally cut down a a real Methuselah of a bristlecone pine -- one of the oldest living trees ever documented -- just so he could count the tree rings? I vaguely recall that it caused quite a stir.

Yes and no. That was a tree later named Prometheus, but the cutting was legal. You can find the story at

Thanks, MRC. Darn shame that the researcher cut that tree down, whether ultimately (and generously) ruled legal or not. At least we now have a law that discourages that sort of thing. I see that a photo of the tree's stump accompanies the article.

When you find a tree stump to study the rings, how do you figure how long ago the tree was cut down, in addition to looking at the rings?

I was in Tehachapi, CA last weekend looking at the stumps and finding the similar patterns and know very little about dendrohronology but sure had questions. I've been taught that the past hundred years were unusual for California in that there has been more moisture than normal and the drought we have been experiencing is returning to what is typical (from Theodore Payne Foundation). However, the lines on the stump were smaller and the closer to the core after 100 rings, the wider they became.

Would this not mean 100+ years ago was more humidity and the past century was actually drier?

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