Scientists say California's historic drought is stressing the state's treasured Giant Sequoia trees, some of the largest and oldest living things on earth.
Koren Nydick, a National Park Service ecologist, says there's more patches of dead foliage in the trees than past years. Giant Sequoias only grow naturally in the Sierra Nevada; they can live 3,000 years and grow to 300 feet.
California is in a fourth year of drought with a record low snowpack and high temperatures.
UC Berkeley tree biologist Anthony Ambrose is climbing the towering trees for a better understanding. He says the research will help identify the most vulnerable groves so officials can manage the forest in future droughts.
Some 75 distinct groves of Giant Sequoias grow mostly in the southern Sierra Nevada.
