High Sierra Topix

End of the sequoias?

Submitted by SHNS on Fri, 04/11/2008 - 13:12.
By MARK GROSSI, Fresno Bee

FRESNO, Calif. -- The 2,000-year-old giant sequoias east of Fresno, Calif., have survived warm spells lasting centuries, but in just 100 years, global warming could snuff them out -- along with many Sierra Nevada species.

Why? The current episode of climate change is moving faster than any warm-up detected in the past 500,000 years, scientists say. Many say car exhaust and other global-warming emissions from human activities may be the reason.

The rising temperatures probably will shorten the Sierra's long, snowy winters and force mass uphill migrations by sequoias, Sierra bighorn sheep, dusky woodrats, rabbitlike pikas and mountain yellow-legged frogs, scientists say.

The warming could mean oblivion for those that can't cope.

"I avoid being an alarmist," said Nathan Stephenson, a U.S. Geological Survey research ecologist at the agency's Sequoia National Park field station. "But there's a chance sequoias won't survive at all if they can't find the right soil conditions at higher elevations."

The bighorn sheep, another mountain icon, might be forced to move uphill away from predators, perhaps marooning themselves on alpine islands away from their food sources, according to scientists.

No one knows what will become of the small, hearty shrubs and animals above 11,000 feet if the Sierra's small glaciers disappear. Glacial ice has dripped precious water into an arid alpine landscape for thousands of summers, but it may last only a few more decades, scientists say.

The warming also probably will force pines and firs to move uphill, along with vast communities of shrubs, herbs and grasses that support wildlife and help purify California's air.

The San Joaquin Valley's poor air quality would suffer further if a warm-up weakens many millions of mature trees, which then would become prone to wildfires and insect infestations. Smoke from fires would foul the air, and decimated forests would not filter pollution.

Another way the Sierra changes would affect people: With less snow, there would be more precipitation in the form of rain. State officials may have to consider expanding reservoirs to store more water.

"These changes are tied to the life cycle of nature, something that affects all of us," said Lara Kueppers, an ecosystems scientist at the University of California-Merced. "There are a lot of reasons to care about what happens."

International visitors probably would notice a difference. They flock to see giant sequoias and Yosemite Falls, which probably would begin peaking earlier each spring in Yosemite National Park.

In the central and southern Sierra, tourists pump millions of dollars into local economies, particularly around Yosemite, Sequoia and Kings Canyon national parks. Yosemite alone has 3.5 million visitors a year.

In Sequoia National Park, four of the five largest trees in the world -- all sequoias -- live in Giant Forest.

The world's largest tree is the General Sherman, 103 feet in circumference at its base and more than 2,300 years old. The Sherman and the other giants live in Earth's last 75 natural groves of giant sequoias, most of which are in the southern Sierra, perched above the Valley.

With widespread root systems, the old giants can tap water sources in many directions during dry times. Their thick, cinnamon-colored bark offers protection from fire, allowing them to live up to 3,000 years.

Birds, mammals, insects and other creatures make these massive trees the center of their lives. For instance, a Douglas squirrel eats sequoia cones, and the weasel-like pine marten preys on squirrels.

But as warming increases, the natural community will be strained. Sequoias would lose their damp, cool habitat between 5,000 and 8,000 feet. The big trees prefer deep, sandy soil at the edge of damp meadows or near streams.

Young sequoias would be forced to grow at higher, cooler elevations. But above 8,500 feet, the soils become more shallow, and there are fewer wet meadows or stream bottoms to provide the water they need.

The species has hung on during past warm-ups, relying on the moisture that remained during more gradual shifts in climate, tree-ring analysis and other evidence show. A more radical change could drain them of resilience and dry up their water sources.

Sierra trees, in general, already are suffering from rising temperatures and less precipitation, according to a study done by USGS ecologist Phillip van Mantgem and Stephenson.

Fir and pine trees are dying at almost double the rate they did 20 years ago, Stephenson said.

"My big concern is that we'll get caught off-guard as this warm-up continues, and a lot of trees will die very quickly," he said. "What kind of surprises will we get?"

(E-mail Mark Grossi at mgrossi(at)fresnobee.com)

(Distributed by Scripps Howard News Service, http://www.scrippsnews.com.)