Ancient redwoods in growth spurt of a lifetime Trees thousands of years old growing at fastest rate of lifetimes

Redwood growth in Richardson Grove State Park in Humboldt County and elsewhere has accelerated. Redwood growth in Richardson Grove State Park in Humboldt County and elsewhere has accelerated. Photo: Ian C. Bates, The Chronicle Photo: Ian C. Bates, The Chronicle Image 1 of / 14 Caption Close Ancient redwoods in growth spurt of a lifetime 1 / 14 Back to Gallery

The last remaining old-growth redwood trees along the California coast and in the Sierra are in the midst of a growth spurt the likes of which has never been seen before, a climate research study revealed Wednesday.

The ancient trees produced more wood over the past century than they have during any other time in their life, a stretch that dates back, in at least one case, a thousand years before the birth of Christ, according to a study released by the Redwoods and Climate Change Initiative.

The growth trend has actually accelerated over the past few decades, said the scientists from UC Berkeley and Humboldt State University who conducted the four-year study.

"It shows these trees are being impacted by something in the environment," said Emily Burns, director of science for Save the Redwoods League, the San Francisco nonprofit that is managing the initiative. "Our hypothesis is that it's because it is warmer. That lengthens the growth season."

The $3 million study, funded by grants and donations, was the most intensive research project ever conducted on the giant trees. The researchers climbed, poked and prodded 137 coast redwoods and giant sequoias on 16 research plots throughout the trees' geographic range.

The result was a dramatic increase in the amount of information available to scientists about the trees, specifically coast redwoods, known scientifically as Sequoia sempervirens.

Record pushed to year 328

Using multiple core samples taken from high in the tree canopy, scientists were able to identify tree-ring patterns, or markers, that were consistent throughout the coast redwood range. The tree-ring record, which revealed drought years and other major weather events, can now reliably be traced back to the year 328, extending the dendrochronological record, as it is called by scientists, by more than 1,400 years.

One tree in Redwood National and State Parks, near Crescent City, turned out to be 2,520 years old, breaking the previous age record for coast redwoods by more than 300 years.

The tree-ring chronology for giant sequoias, known scientifically as Sequoiadendron giganteum, goes back to the year 474. The largest of these Sierra giants, which generally live longer than their coastal cousins, was 3,240 years old, according to the study.

"We now have the most complete and thorough cross-dated chronologies for coast redwoods at sites throughout their range," said Allyson Carroll, a Humboldt State dendrochronologist. "These can be used for many applications, including fire histories, climate studies, dating of archaeological buildings and dating extreme climate events."

Growth spurts

Burns said the plan is to chart the health of the trees over time and use laboratory analysis of carbon and oxygen isotopes to figure out how the trees have reacted to past weather conditions. By studying the rings, scientists hope to be able to forecast how the redwoods will change as the Earth warms up.

The new chronology is what helped Stephen Sillett, a professor of forest ecology at Humboldt State, calculate wood growth over time. What he found was that both redwood species grew at a relatively stable rate for 650 years and then, about 100 years ago, suddenly began to grow faster. There was a slight slowdown in the 1950s and 1960s, and then in the 1970s the tree growth accelerated faster than ever, his research found.

"Wood production increased during the last century in both species," wrote Sillett, a pioneer in research conducted high in the redwood forest canopy, "and the pace of increase was unprecedented in our tree-ring record."

More sunshine

Anthony Ambrose, a postdoctoral research fellow at the UC Berkeley department of integrative biology, has said the growth spurt is most likely caused by increased sunshine along the coast and more carbon dioxide in the atmosphere.

A 2010 study documented a 33 percent decrease in the amount of fog and cloud cover along the Northern California coast since the early 20th century. Meanwhile, rainfall has kept the forests wet, Burns said.

"What we're seeing is that the redwoods are growing even better as the fog has declined," Burns said. "It's fantastic. For me this is a really hopeful story about the redwoods."

The data are important not only for ecological reasons but also because ancient redwoods could become a valuable commodity in California's emerging carbon market. Redwoods store three times more carbon than other types of forests, according to researchers, and have unique decay-resistant qualities that allow them to hold carbon even after death, thereby keeping climate-warming gases out of the atmosphere.

The 1739 mystery

The work, however, is far from complete. Researchers know, for instance, that something big happened along the Northern Coast in 1739. The tree rings in multiple redwoods and other trees in Northern California and Oregon were tiny that year, indicating some sort of extreme climatic event, Carroll said. There were no known volcanic events that year, she said, and nothing has yet shown up in the historic record.

Meanwhile, she said, tree-ring data from Big Sur, the southern-most study area, show that the trees have been affected more adversely than the trees in the north by past drought events.

"It is something we haven't quite pinned down," Carroll said. "This is why we need to explore further and figure out what's been happening throughout these chronologies,"

The research team will present its findings during a daylong symposium Wednesday in Berkeley that the public can follow on Facebook, Twitter and Instagram.