Forest Facts

A giant step for understanding redwood tree rings

Allyson Carroll views tree cores under the microscope at Humboldt State University.

Allyson Carroll views tree cores under the microscope at Humboldt State University.

Today, Redwoods and Climate Change Initiative scientist and my colleague, Allyson Carroll, shares her perspective on how she decodes the history of redwoods from tree rings:

Imagine finishing a massive puzzle, one involving nearly half a million pieces and taking years to complete… it feels good when that puzzle is done! For this puzzle, the “pieces” are tree rings and this week our research was published detailing the first range-wide network of coast redwood tree-ring chronologies and their sensitivities to historical climate conditions. Developing a tree-ring chronology is more than simply counting rings; it’s putting a precise calendar year on each ring. Think of a tree’s rings like a fingerprint, there is a pattern of larger and smaller growth rings dependent on the climatic conditions experienced by that tree. Coast redwoods are notorious for being difficult to crossdate – or match the ring width patterns across a population of trees – with many anomalies and discontinuous or “missing” rings. So, the first step toward many research applications is simply determining the correct dates for each ring.

Coast redwood tree rings showing discontinuous and tight rings. Photo by Allyson Carroll.

Coast redwood tree rings showing discontinuous and tight rings. Photo by Allyson Carroll.

Key to our success was taking increment cores from multiple heights along the main trunks of coast redwoods and giant sequoias. This provided enough replication to solve the puzzle of each tree. While I was able to climb several giants to collect cores, the vast majority of my time was spent in the lab looking through the microscope, piecing together each tree’s past. With crossdated series we were also able to compare the growth rings to climate histories at our study locations, to determine what climate variables correlate with the year-to-year variation of ring widths. I encourage you to read our research results, as one prong of the many aspects of the Redwoods and Climate Change Initiative.

Read Allyson and colleagues’ new publication here.

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