Decoding Tree Rings

Tree ring analysis provides critical information on tree ages and how redwoods throughout California respond to climate conditions.

Through the work of RCCI scientist Allyson Carroll of Humboldt State University, we now have comprehensive tree ring records for both species of redwood trees. Collecting core samples from the trees in our 16 plots allows us to count annual growth rings, enabling an accurate estimation of tree ages. This tree ring analysis also provides critical information on how redwoods throughout California are responding to current conditions, and how they have responded to their climate in the past centuries, and even millennia. Currently the cross-dated dendrochronology record for coast redwoods extends back to 328 AD; for giant sequoia it reaches 474 AD.


Scientists take pencil-thin cross sections from trees to count their growth rings. Growth rings (or tree rings) can vary in width and tell a story of the tree’s growth history and what was happening in the forest during a particular year. The science of studying tree ring patterns is called dendrochronology.

Initial Results

  • The Initiative produced the most comprehensive tree-ring record ever collected for coast redwoods and giant sequoias, allowing us to see how climate events such as droughts, fire and flooding have affected redwoods’ growth across history.
  • RCCI scientists discovered the oldest-known coast redwood, at 2,520 years old!

Now, through stable isotope analysis, our scientists are uncovering the climate history recorded in redwood tree rings. Water sources leave a stable isotope imprint in the cellulose of wood produced annually. These analyses will help us learn more about how redwoods grew over the last millennia and how the climate changed. See the video of Todd Dawson presenting his findings at the 2013 Redwood Ecology and Climate Symposium.

Review RCCI Research Abstracts and watch the video above to learn more about these initial results. Read Allyson Carroll’s publication (external link) to learn more about her work as part of the RCCI.

The results will help us make informed decisions about how to protect and restore redwood forests as they face rapid climate change.

Your generous support helped to make this research possible and funds are still needed to continue this critical work. The more we know about the redwoods, the better we can look after them. We look forward to learning and sharing much more through the important work of the RCCI program. Thank you.