Oct 2, 2009

Flora, fauna altered by global warming

SACRAMENTO -- When Berkeley biologist Chris Conroy and colleagues went looking in Yosemite for the alpine and shadow chipmunks, they had trouble finding mammals that an earlier generation of Berkeley scientists found everywhere in the park.

The California pocket mouse, ordinarily making its home in chaparral, was found 2,000 feet higher than where it was 90 years ago. Scientists likewise had to hike 1,000 feet higher to find the wood rat and California vole.

The pinon mouse, typically found on dry, eastern Sierra slopes and never in Yosemite, today is found all over the park, along with another new arrival, the harvest mouse.

Something is rearranging California's flora and fauna, and climatic shifts are topping the list of explanations. Sierra snows are melting one to three weeks earlier than historically, ushering in an early spring and drier soils and forests, particularly at middle elevations.

For the better part, that's where climate researcher Anthony Westerling has found an explosion in wildfires across the American West. The number of wildfires has quadrupled in the last 17 years and the burned acreage has swelled almost seven times over, mostly at middle elevations.

"There's a really strong correlation here between temperature and forest fires, and it really picked up since the late 1980s," Westerling said Friday in Sacramento at the California Energy Commission's third annual conference on climate change.

For now, the greatest wildfire risk in California is on the southern coast and in the southern Sierra foothills. But every computer simulation of greenhouse-gas warming shows higher fire risk in California, and the greatest increase in risk is in Northern California, Westerling said.

If the rate of fossil fuel burning continues to accelerate at its current pace, the greatest probability for large property losses shifts to the Sierra foothills northwest of Sacramento, he said.

Whether there will be forests to burn there is another question. Ponderosa pines in the northern Sierra foothills are getting harder to find where scientists mapped them in the 1930s.

Jim Thorne, an environmental science researcher at the University of California, Davis, compared the latest vegetation maps with ones made by Berkeley scientists in the 1930s and '40s. In Eldorado County, he found, the forests have shifted 16 miles toward the mountains and more than 1,700 feet higher, climbing three meters a year on average since the '30s.

"I think a lot of this might be due to climate change," Thorne said Friday.

Ordinary wildfires are claiming the trees, but Thorne said he suspects the replacement seedlings are encountering warmer, drought- like conditions and failing. Those warmer conditions are apparent when Thorne looks at monthly minimum temperatures in the foothills, which usually are nighttime cools.

In the early '80s, those average minimums for Lake Tahoe in May and October rose above freezing and never have come back down.

In Yosemite Valley, the coolest temperatures in November, March and April went past freezing in or before 1990 and haven't come back.

Winter in Placerville no longer is reliably white. Nighttime temperatures in December, January and February have averaged above freezing since the early 1990s.

"There are no longer any months at Placerville that remain frozen," said Thorne.

The changes aren't unique to winter. During last summer's heat wave, nighttime in Fresno brought virtually no relief, with temperatures staying as high as 90. That makes sense for southern desert places like Needles and Death Valley, but not the Central Valley, said Kelly Redmond, director of the Western Regional Climate Center in Reno.

"That's just way beyond what I would have expected to see," Redmond said. "And we're seeing it all over the West."

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