Coastal Redwoods Used in Climate Reconstruction for First Time

Researchers from the University of Washington and Southern Oregon University have developed a new method of using coastal redwood trees in climate assessment studies.

Many coastal redwood trees are as magnificent as they are old. The towering trees - the world's tallest living thing - have long inspired and captivated people, but have been of little use to scientists attempting to use their growth patterns to glean historic climate data. The trees grow too erratically to help with typical climate reconstruction studies.

But the UW team has developed a way to use data collected by the trees to paint a picture of past climate conditions by using oxygen and carbon atoms in the wood to detect fog and rainfall in previous seasons.

The study's corresponding author Jim Johnstone, of the UW-based Joint Institute for the Study of the Atmosphere and Ocean, said the research was "really the first time that climate reconstruction has ever been done with redwoods."

"Redwoods are restricted to a very narrow strip along the coastline," Johnstone said, adding that the naturally foggy surroundings are recorded in the trees' bark. "They're tied to the coastline, and they're sensitive to marine conditions, so they actually may tell you more about what's happening over the ocean than they do about what's happening over land."

Johnstone and his colleagues' study traced 50 years of past climate conditions using Northern California coastal redwoods and cross-referenced their assessment of climate through the trees with actual climate data.

The data gleaned from the trees proved to be accurate, which the researchers contend is enough evidence to rely on the trees to assess climate data from up to 1,000 years ago.

"We actually have two indicators that we can use in combination to determine if a particular summer was foggy with a little rain, foggy with a lot of rain, and various combinations of the two," Johnstone said, adding that by analyzing the proportions of of oxygen isotopes O-16 and O-18 in the wood the team was able to measure levels of fog and rain at the time the molecules became embedded in the wood.

Another study has linked the the amount of West Coast fog with the surface temperature of the ocean, which suggests that redwoods may be able to tell us something about the long-term patterns of ocean change and natural variability cycles, both of which will help distinguish between natural and anthropogenic climate change.

"It's possible that the redwoods could give us direct indication of how that's worked over longer periods," Johnstone said. "This is just a piece that contributes to that understanding in a pretty unique place."

Johnstone and his colleague John Roden's research is published in the Journal of Geophysical Research-Biogeosciences.