Everyone knows how to determine the age of a tree that’s just been cut down: count the rings. But did you know that the same general strategy can be used to track ancient weather patterns, explain the rise and fall of great empires, and construct detailed histories of long-vanished societies that left no written records? I do now, thanks to “Tree Story,” Valerie Trouet’s well-written and engaging dive into the fascinating science of dendrochronology.
Trouet, who has dedicated her career to the study of tree rings around the world, tells a series of multilayered tales that play out on different time scales. Part memoir, part science explainer, and part world history, her book reads like a fascinating conversation.
We learn about the science of dendrochronology, which began in the early 20th century in the sparsely-forested American Southwest, of all places, and how dendrochronologists assemble timelines that can span centuries with single-year precision. We also ride along with Trouet down muddy Siberian roads, climb high into the mountains of Greece, and sample centuries-old trees in California. She escorts us through her colleagues’ work as well, explaining how other dendrochronologists have tackled such challenges as sampling bald cypress trees in swamps and aligning the rings of ancient building timbers.
All of this fieldwork ends up back in the lab, where researchers assemble databases of tree ring thicknesses and use sophisticated computing techniques to extend their chronologies further and further into the past. This is where we get juicy stories about famous Viking explorers, Ancestral Puebloan cliff dwellers, the doomed English settlers of Roanoke Island, and more.
Because tree rings can pinpoint the dates of droughts, pluvials, wildfires, storms, and other major environmental events, they provide a global historical clock and weather report with extraordinary accuracy. This detailed climate record tells us, for example, that droughts and crop failures probably helped topple Rome, and that Attila the Hun’s success stemmed partly from a long stretch of good weather.
A striking aspect of these stories is the interconnectedness of them, when viewed from the trees’ perspective. We tend to think of different continents having distinct histories that only touch at specific points, but in fact weather and climate phenomena have always operated at a global scale, and always wielded immense influence on human affairs. To an informed interpreter like Trouet, the trees in the Sierras remember troubles in imperial China, and European forests speak of ancient African droughts. It’s been a small world all along.
The trees also offer a warning; in this vast, global library of long-running diaries, every volume is telling us that we are now living through a period of climate change unprecedented in millennia.
Trouet doesn’t dwell on our current climate catastrophe, but instead lets it percolate naturally through the narrative. Having outlined the drastic impacts that far less substantial perturbations have had on earlier civilizations, she mostly lets the reader ponder what this means for the future of our own. That makes the ending of the book seem a bit abrupt, but perhaps we’ll get another book from her that takes a deeper dive into this issue. In the meantime, “Tree Story” is a tale well worth reading.