California continues to suffer under a historic drought.The state has received very little rainfall over the past four years.
California is famous for its huge sequoia trees.They are among the largest and oldest living things on Earth.But scientists say the trees are suffering because of the lack of water.
Now the National Park Service is studying how the drought has affected the sequoias and what can be done to help them survive.
Anthony Ambrose is a tree biologist with the University of California,Berkeley.One recent day,he slowly climbed up a giant sequoia in California's Sierra Nevada Mountains.The Sierra Nevada range is the only place on earth where sequoias 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 you know a thousand years or more."
Sequoias can grow to a height of over 90 meters tall.The bottom of the tree can be up to 15 meters wide.Some trees are more than 3,000 years old.
The Sierra Nevada range once had plenty of water because of mountain streams.But less water is available now because of the drought.Each sequoia needs more than 3,000 liters of water a day.The trees are now getting much less.Some of them are showing signs of thirst,says Anthony Ambrose.
"We've observed some unusual and abnormal levels of foliage die-back,which haven't been observed in the park before."
Researchers are using scientific equipment in tree canopies to help measure air temperature and humidity levels.They also are studying sequoia seedlings,information from individual trees and images collected by aircraft to measure the seriousness of the danger.
One possible solution would be to cut down less important tree species because other plants compete with the sequoias for water.Koren Nydick of the National Park Service is one of the scientific investigators.
"They'll have more water than they would have in a denser forest,more nutrients and light and therefore be more resistant and resilient to these hot droughts they're faced with in the future."
Scientists say that over thousands of years,sequoias have survived many droughts,forest fires,insect infestations and other disasters.Scientists say the sequoias will probably survive this drought,unlike many other California trees.