Can Redwoods Survive Climate Change?

by Betsy Herbert

Published 02/25/12 in the Santa Cruz Sentinel

It’s hard to imagine that the iconic coast redwoods (Sequoia sempervirens) could be vulnerable to extinction. After all, redwoods have demonstrated legendary resilience to some fairly severe onslaughts. Even after massive clear-cutting, redwood forests have rebounded--as they have over the past century in the Santa Cruz Mountains--with a force reminiscent of Stravinsky’s Rite of Spring. Redwoods are also renowned for their resistance to both fire and disease.

Yet, redwoods are at risk. The World Conservation Union (IUCN) has rated coast redwoods as vulnerable to extinction, primarily because of impacts from logging and development over the past 200 years. Throughout the current range of the redwoods--from Big Sur up to southern Oregon--only 4% of the old-growth forest now remains in tact.

And the onslaught continues. Redwoods are still subject to clear-cutting in many areas. Throughout their range, they are threatened by conversion into vineyards, housing development, invasive species, fire suppression, and habitat fragmentation. And now, climate change.

Scientists are studying how climate change is impacting forest ecosystems throughout the world, but regional climate conditions and forest types are widely variable. Generally, the concern is that rapidly changing climate conditions such as increased temperatures, drought, and altered precipitation patterns may outpace a forest ecosystem’s ability to adapt, especially if that forest is already stressed and/or degraded.

How will climate change affect California’s redwoods, and what can be done to ensure that redwoods survive?

Save-the-Redwoods-League, a San Francisco based land trust, is sponsoring a team of scientific researchers to investigate these questions. The 10-year project, “Redwoods and Climate Change Initiative” (RCCI) aims to quantify how climate change, in combination with other stressors, is affecting redwoods. [Disclosure: I serve on RCCI’s leadership task force].
RCCI’s team of scientists from Humboldt State University and UC Berkeley have established 16 forest plots throughout the range of the coast redwood and its cousin, the giant sequoia of the Sierra Nevada. They’ve installed weather stations in the treetops to collect climate data for each site. They’re also exhaustively measuring the height, circumference and branch structure of the giant trees to track their precise growth rate. And, they’re studying annual tree ring data, going back 1,000 years to determine how redwoods have historically responded to changing conditions, including temperature, precipitation, fog, and fire.

One of RCCI’s lead scientists, Todd Dawson, has documented how redwoods use fog to supply most of their summer water. Of special interest then, is how climate change may alter fog patterns within the range of redwoods. Dawson’s preliminary evidence shows a 30% decline in the number of fog days in the region over the past 60 years.

Climate change is also expected to bring warmer and windier conditions to northern California, along with increased wildfire frequency and severity, according to a 2004 study by US Forest Service and Lawrence Berkeley National Laboratory scientists. The study turned out to be right on target for Santa Cruz County, where the 2009 Lockheed Fire burned 7,800 acres in Bonny Doon and Davenport, including 2,400 acres of redwoods. Fortunately, CalFire’s post-fire report found that the Lockheed fire “will not have long term detrimental ecological effects to the redwood forest type.”

As scientists are busy assessing the impacts of climate change on redwoods, what can be done to protect these forests? Forest scientists emphasize increasing the adaptive ability of forests to prepare for uncertainty. Minimizing soil disturbance, protecting and buffering old-growth reserves, reducing forest road densities and increasing wildlife connectivity are all recognized ways of helping forests become more adaptable to future impacts.