VOA常速英语2015--长期干旱影响加州的红杉

（单词翻译）

Long Drought Affecting California’s Sequoias 长期干旱影响加州的红杉

California is suffering under a historic four-year drought and scientists say even the state's famed sequoia¹ trees are feeling the pain. The National Park Service has started detailed² research to see how it can help the oldest living things on earth survive.

Slowly and painstakingly³, University of California tree biologist Anthony Ambrose climbs up a giant sequoia in California’s Sierra Nevada mountain range, the only place on earth where these magnificent trees live.

“It’s an amazing experience to be able to climb up into these things and know that it's been growing in this same spot for a thousand years or more,” he said.

Sequoias grow over 90 meters tall, their trunks are up to 15 meters wide and some of them are more than 3,000 years old.

Once-rich mountain streams have dwindled⁴ to trickles⁵ and the trees - that each need more than 3,000 liters of water a day - are now getting much less. Some of them are showing signs of thirst.

“We've observed some unusual and abnormal levels of foliage⁶ die-back, which haven't been observed in the park before,” Ambrose said.

Sensors⁷ installed in tree canopies⁸, examinations of seedlings⁹, data from individual trees and images collected by observational planes will help scientists measure the seriousness of the danger.

One possible solution would be to cut down less important species of trees that compete with sequoias for water.

“They'll have more water than they would have in a denser¹⁰ forest, more nutrients¹¹ and light and therefore be more resistant¹² and resilient to these hot droughts they're faced with in the future,” said Koren Nydick, who is with the National Park Service.

Scientists say that over thousands of years, sequoias have gone through many droughts, forest fires, insect infestations¹³ and other calamities¹⁴, so they will probably survive this drought, unlike many less-resilient California trees.