So Far, The World’s Tallest Trees Are Handling Climate Change OK — But They Aren’t Out Of The Woods Yet



CREDIT: AP/Kevork Djansezian

Two species may be making it through climate change unscathed — at least for now.

New research has found that in spite of — or perhaps even due to — rising temperatures, coast redwoods and giant sequoias in California are growing at their fastest rates since the 1970s. The research is part of a study that’s expected to continue for at least another ten years, the initial findings of which were presented at a Berkeley symposium Wednesday. So far, by examining the tree’s ring data, the researchers have created a chronology of the redwoods’ girth expansion since the year 328 and the sequoias’ growth since 474. The redwoods, in particular, have seen large growth spurts recently, with rates up to 45 percent higher today than at any time in the last 200 years.

There are multiple explanations for why redwoods — the world’s tallest trees — and sequoias could be growing so quickly in California. The surge could be climate related — researcher Stephen Sillett told the LA Times that the trees could be responding to an extended growing season made possible by rising temperatures in the Sierra Nevada. Another researcher, Emily Burns, said the reduction in fog due to rising temperatures might mean the trees are getting more sun. But it could have nothing at all to do with climate change: Sillett said a reduction in North Coast air pollution also increased light in redwood forests, which could have upped the trees’ growth rate, and wildfire suppression in the area may have also played a role.

The scientists aren’t sure yet which of these factors contributed most to the trees’ growth. But they warn that, while the growth spurt is a promising sign, it isn’t necessarily a permanent one. If rising temperatures bring less rainfall to the California coast, the trees — especially young sequoia seedlings, which studies have shown have a hard time surviving when soil moisture drops below a certain threshold — could suffer.

“There’s a tipping point,” the research team’s lead scientist Todd Dawson told the San Jose Mercury News. “As we go into warmer and drier times, particularly with snowpacks on the decline — which means less water for giant sequoias — we’re concerned that this growth surge is probably not going to be sustainable.”

The future looks uncertain for other types of trees as well — previous studies have yielded varying results on trees’ ability to adapt to climate change. A 2011 study found more than half of tree species in the eastern U.S.were not adapting to climate change as well as models had predicted: nearly 59 percent of the species showed signs that their habitat ranges were getting smaller, contracting both from the north and south, and that only 21 percent seemed to be moving their ranges northward as temperatures warmed. Last month, a study’s findings were a bit more hopeful: the research found trees in some parts of the world may use water more efficiently as atmospheric carbon levels rise, which could mean the trees will be able to become more drought-resilient. And a 2010 study also provided some hope for the future of forests, discovering that ancient rain forests bloomed with diversity, rather than went extinct, during the Paleocene-Eocene Thermal Maximum, an era associated with rapid warming and doubling of CO2 levels.

But other factors associated with climate change are already making survival difficult for many trees. Some face harrowing challenges — warmer winters have allowed mountain pine beetles to expand their range into higher latitudes, regions that were off limits to them in the past. The insects have killed millions of acres of trees from New Mexico to British Columbia, and have even reached as far north as Alaska. The beetles prey most heavily on old trees or those weakened by drought or wildfires — two factors that climate change is already exacerbating in many parts of the world. Wildfires have consumed more than 6.25 million acres of forest in Alaska alone — an area which, as the EPA notes, is roughly the size of Massachusetts. And hundreds of thousands of U.S. trees died during last summer’s historic drought, and scientists predict many more weakened by the drought will continue to die in in the next two to three years.