Are the California redwoods in danger because of the drought?

Dear EarthTalk: Are the California redwoods in danger because of the drought?

— Jesse Pollman, Seattle, WA

California is home to two of the three redwood tree species: coast redwoods and giant sequoias. The coast redwood is the Earth’s tallest tree, growing more than 360 feet tall, with a trunk that can extend to 24 feet wide. The “General Sherman” giant sequoia tree at Sequoia National Park in California’s southern Sierra Nevada mountain range is the “undisputed King of the Forest,” being not only the largest living tree in the world, but the largest living organism, by volume, on the planet. General Sherman is 2,100 years old, 2.7 million pounds, 275 feet tall and 100 feet wide at its trunk.

Redwood forests offer shelter to many animals, including mountain lions, American black bears, Roosevelt elks and mountain beavers. According to the National Park Service, approximately 280 species of birds have been recorded within the boundaries of redwood national and state parks. Just over 800 bird species occur in all of the United States, so that equates to approximately one third of the country’s birds.

“Redwoods are an iconic key species,” said Anthony Ambrose, a postdoctoral researcher with the Department of Integrative Biology at the University of California (UC), Berkeley. “They’re the tallest, oldest, and largest trees in the world. Everybody around the world knows about them. People love them, even if they’ve never visited them. They’re beautiful forests and beautiful trees.”

For the past four years, California has been suffering a grueling drought. Agricultural economists at UC Davis recently calculated that the drought will cost the state $2.74 billion in 2015. Drought can reduce tree growth rates and may even lead to tree death. Coast redwoods receive up to 40 percent of their water supply from fog, which is created from warm, moist air rising from the cold surface waters of the Pacific. Giant sequoias grow in mountain habitats where an abundant winter snowpack recharges the groundwater they depend upon and use in the summer. However, during the past two winters, much of the giant sequoia range had little to no snowpack. As a result, groundwater levels have dropped, sometimes below the roots of immense giant sequoias that are greater than 1,000 years old, says Todd Dawson, a UC Berkeley Professor of Integrative Biology who’s been studying redwood ecology and physiology for over 25 years.

For the coast redwood, the drought impacts are not as severe as they seem to be for the giant sequoia. Trees at the edges of the coast redwood range, including the southern end of the range in the Santa Lucia Mountains south of Big Sur, seem to be the most affected. Here, young trees have lost a lot of their leaves, and have not grown very much, if at all, Dawson said.

“Many trees are experiencing the highest levels of water stress we’ve ever measured. We’ve not seen much tree mortality, but many trees have thin crowns and do not look healthy,” Dawson said. “Our biggest question is just how far can these trees be pushed?  If the winter does not bring good rainfall and a normal snowpack throughout the state I am not sure how our state trees will do. We are likely to see some mortality as we are seeing in some of the pines and firs in California. But how bad this will be – only time will tell.”