Hearty giant sequoias threatened by 'unusually hot' Rim Fire

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UPDATE: Massive wildfire near Yosemite one of California's worst at 149,780 acres (map)

As the Rim Fire continues to burn near Yosemite National Park, firefighters are turning their attention to two patches of giant sequoias trees.

The Tuolumne and Merced groves are in the projected path of the fire, though they are still several miles from the actual blaze.

Over the weekend, firefighters began clearing brush, laying down overlapping sprinkler systems and even using controlled burns to create a fire dampening barrier around the sky-high trees.

Some of these iconic sequoias are 2,000 years old. They've lived though plenty of wildfires, but the intensity of the Rim Fire may be more than even these mighty plants can handle.

Heartier than most

Sequoias are known for their towering height (some grow up to 300 feet tall), and their massive girth (25 feet or more in diameter). They also have unusually thick bark, according to Nate Stephenson, research ecologist with the US Geological Survey.

Most trees have only a few inches of bark, but giant sequoias can grow anywhere from 8 inches to 3 feet of fibrous tissue on their lower trunks.

“It helps insulate the trees trunk from the effects of fire,” said Stephenson.

Sequoia wood is also rich with tannins, a compound often associated with red wine. Tannins are naturally fire resistant and help provide an extra layer of defense for the trees.

When they are damaged in a fire, sequoias are really good at regrowing lost branches. A single tree can lose up 95 percent of it's crown and still rebound, said Stephenson.

Fire dependent species

In fact, sequoias need fire to reproduce.   

"The cones of the giant sequoia often need extreme heat to open and to release their seeds,"  said Tom Medema, information officer for Yosemite National Park.

Once on the ground, the nutrient rich soil left behind by a fire creates the perfect home for a sequoia seed to sprout. The lack of other plants competing for water and sunlight aid in the seedling's survival.

Too high, too dry

Many sequoias show scars from past fires. When they burn at the base they often have char marks that can heal over time. The danger in the Rim Fire is that it's burning much higher, at the level of tree tops.

This pattern is known as a "crown fire," said Medema. Crown fires are intense and burn fast. Even giant sequoias cannot survive if all their branches are burned in such a blaze.

The Rim Fire is unusually hot, "because of the dryness of all those fuels."

Those factors create a potentially fatal combination for California's beloved trees... if the fire reaches them. For now, officials are working hard to stop that from happening.

"As many things as we can do to protect those natural and cultural resources, we are doing," said Medema.

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