September 5, 2008

Giant Sequoias Could Be Harmed By Climate Change

Warming temperatures will cause California's giant sequoia trees to die off more quickly unless forest managers plan with an eye toward climate change and the impact of a longer, harsher wildfire season, federal researchers warned.

Recent research from the U.S. Geological Survey said hot and dry weather over the last two decades already has contributed to the deaths of an unusual number of old-growth pine and fir trees growing in Yosemite and Sequoia National Parks.

Nathan Stephenson, a research ecologist with the USGS Western Ecological Research Center, warned that in the next decade, climate change also could start interfering with the giant sequoias' ability to sprout new seedlings.

Stephenson is just one of several scientists speaking Thursday at a government agency symposium on how global warming could affect the Sierra Nevada.

"The first effects of climate change that we're likely to see is that the giant sequoias will have trouble reproducing because their root systems don't work as well when temperatures warm," said Stephenson. "After that, I wouldn't be surprised if in 30 years we see their death rates go up."

An inland cousin to the tall California coast redwood, Sequoiadendron giganteum can become 2,900 years old and bulk up to more than 36 feet in diameter, making them among the world's most massive living things.

A team of tree demographers, including Stephenson, monitored the health of pines and firs growing in the two southern Sierra Nevada parks from 1982 to 2004.

They found that as both temperatures and summer droughts increased over that period, the trees' normal death rate more than doubled, and stands became more vulnerable to attacks from insects or fungus.

Scientists say that while those species have a faster life cycle than the ancient sequoias, the mortality rates can help predict what may happen to the massive organisms as temperatures increase as predicted an average of 3 to 10 degrees Fahrenheit statewide by the end of the century.

Constance Millar, a senior research scientist with the U.S. Forest Service, said a lot of our most cherished species are at stake. "Rather than just managing forests for the plants we see growing there today, we're now having to look forward to think about what might thrive there in 100 years."

Native flora and fauna throughout the 400-mile-long Sierra Nevada mountain range are already under stress from a warming climate, and federal land managers have started monitoring wildlands to understand how they're transforming.

Based on what they've seen on the ground, some officials have already started making changes.

Millar said the Forest Service recently redrew its decades-old maps for where to place fire breaks along the Sierra Nevada, moving suppression efforts down from the ridge lines to lower regions where scientists now believe habitats are at risk from wildfires.

The mountain-dwelling American pika, or rock-rabbit is one local species troubled by rising temperatures. The 6-inch-long rodent thrives in cool, mountaintop climates, but at higher temperatures they can overheat and die within hours.

Biologists say the population has been dwindling and drifting to higher elevations and fear it eventually could run out of mountain.

It could take years to understand how different animals and plants are influenced by not only rising temperatures, but fires, pollutants, forest management practices and other change agents, park officials said need to proceed cautiously.

"Right now, we're going to focus our efforts on the big icon for the parks, the giant sequoias," said Craig Axtell, superintendent of Sequoia and Kings Canyon National Parks. "But we may find that other problems come up down the road that we don't even know about."


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