Climate Change Killed Thousands of Trees
Pat Brennan - The Orange County Register
Drought, heat drive vegetation upslope in mountains east of Orange County
Climate change has killed thousands of trees and forced native plants to retreat to higher elevations on a Southern California mountain range, the dramatic results of a new study by UC Irvine climate scientists show.
And while it remains unclear whether localized changes in climate or global warming is to blame, the study paints an ominous picture of what might be in store as planetary temperatures continue to rise.
The findings could have profound implications for many outdoor activities, and for the management of Southern California's wild lands.
"It's hard to say what this wouldn't impact," said Anne Kelly, the study's lead author and a UC Irvine graduate student in Earth System Science. "Recreation, land management, fire abatement: anything that has to do with nature is going to be affected by this."
Drought and warmer temperatures pushed trees such as Jeffrey pines and white firs an average of 213 feet upslope on the Santa Rosa Mountains, south of Palm Springs, over the 30-year period covered by the study. The trees and shrubs died at lower elevations.
"I was really surprised to see the signal was so strong and so clear across the entire mountain range," Kelly said. "Drought is a huge, huge problem."
Kelly, an ecophysiologist, and Earth System Science professor Michael Goulden examined trees, shrubs and other native vegetation on the north face of the Santa Rosas.
Other scientists have noted shifts in the ranges of birds and other animals, as well as plants, as a result of changes in climate.
But in one of the first studies of its kind, the scientists compared ground-based observations and direct measurements of plants over a 30-year period. They focused on a 7,300-foot, vertical cross section that spanned a variety of plant communities, from desert scrub at the bottom to pine forests at the top.
The area had been covered by another scientist in a 1977 plant survey; Kelly and Goulden returned to the same area for a detailed resurvey of the plants in 2006 and 2007.
Nine out of 10 species on which the researchers focused most intensively died at lower elevations and moved upslope.
But Kelly said the scientists saw essentially the same effects on all the 141 plant species they examined, from sea level to 8,400 feet.
"That was the shocking thing about this study," she said. "It was consistent with desert plants down at sea level as well as conifers up in the mountains."
During the same period, mean temperatures in the area increased by more than a degree Fahrenheit; severe drought also struck the area from 1999-2002.
A recent European study yielded similar results, Goulden said.
Because the scientists focused on the Santa Rosa Mountains, she said, they were able to rule out other possible reasons for changes in vegetation, including air pollution and excessive wildfire.
Measurements of carbon dioxide in the area showed a lack of air pollution that would have toxic effects on plants. And unlike in many Southern California mountain ranges, the Santa Rosas have not seen a major fire since the 1940s.
While such effects complicate the picture in other Southern California mountain ranges, the study suggests these, too, might well be susceptible to similar climate-driven changes.
The climate change in question might be the "heat island" effect observed throughout Southern California: a rise in temperatures over decades linked to the covering of more land surface with buildings and asphalt.
And while it is not possible to establish a firm connection between the scientists' findings and global climate change as a whole, the results are consistent with the predictions of computer models that take global warming into account.
"The best thing about this study is that, regardless of why there's warming, regardless of why there are more droughts, this is kind of a preview of what global warming could do in other places in the world," Kelly said.
The study will be published this week on the Proceedings of the National Academy of Sciences Web site.
Contact the writer: 714-796-7865 or pbrennan@ocregister.com.
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TREE DEATH The death of white firs in the San Jacinto Mountains is attributed to climate change in a new UC Irvine study. COURTESY, UC IRVINE |
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