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Monday, 11 December, 2000, 19:15 GMT
Largest tree a mere stripling
fire among sequoias
Fire is a risk for the sequoia groves
By environment correspondent Alex Kirby

Scientists now believe the world's largest tree may be far younger than previously estimated.

The age of the tree, a giant sequoia in California, was originally put at between 5,000 and 6,000 years.

Improved sequoia dating techniques brought that down to somewhere between 2,500 and 3,500 years.

But the latest estimate suggests the tree, known as General Sherman, is perhaps no more than 2,200 years old.

However, its other vital statistics remain unchallenged. At 90 metres (275 feet) in height and nine metres (30 feet) across at the base, the conifer is still recognised as the largest (by volume) tree on Earth.

Rapid developer

The new estimate is reported by Dr Nate Stephenson, an ecologist with the US Geological Survey's Western Ecological Research Center.

Writing in the botanical journal MadroZo, he said: "The Sherman tree isn't so large because it's exceptionally old, but because it's growing so fast.

"Each year, it adds enough wood to make a tree one foot (30 cm) in diameter and more than 100 feet (30 metres) tall.

"The tree's extreme bulk, more than 10 times larger than a blue whale, has long led people to believe that its age was also extreme.

"The relative youth of the world's largest tree comes as something of a surprise."

Smaller and older

Dr Stephenson said rings examined in tree stumps had shown that much smaller sequoias were much older, reaching ages of more than 3,200 years.

The revised estimate relies on tree ring measurements from pencil-thin, 30-cm- (1-ft-) long cores of wood removed from near General Sherman's base, and mathematical formulae based on measurements from hundreds of sequoia stumps.

Sherman WERC
More accurate measurement could harm the famous tree
Dr Stephenson and his colleagues developed their dating technique as part of a study to determine the effects of past changes in climate and fire frequency on giant sequoias. But they acknowledge that General Sherman's origins remain a mystery.

"The new age estimate of about 2,150 years could still be off by centuries," Dr Stephenson said.

"Getting a precise age measurement would require boring a hole several inches wide all the way to the centre of the tree."

Vibrant teenagers

Bill Tweed, of Sequoia and Kings Canyon national parks, said: "We don't want to risk harming this special tree by removing such a large core."

General Sherman is not the only sequoia to have undergone rapid rejuvenation.

Dr Stephenson said the Grizzly Giant tree of Yosemite national park was no more than about 1,800 years old, while General Grant, known as the nation's Christmas tree, probably dated from about AD 350.

"Most of the largest sequoias are really just middle-aged", he said. "But they're still growing like teenagers."

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