sequoia sequoia sempervirensAlso known as coastal redwood, it may be the tallest tree in the world, but even the tiniest sample of its wood can reveal a past. analyzed thousands of pencil-width cores extracted from and dead trees to build a set of tree-ring chronologies for coastal sequoias, the first database of their species. These records date back to his fourth century and allow scientists to pinpoint the precise timing of climate change, earthquakes and other environmental phenomena.
climbing for science
“By the end of the day, our arms are sore.”
Between 2005 and 2021, researchers working in California and Oregon collected tree cores from hundreds of coastal redwoods. Each extraction was a massive undertaking. Alison CarrollA dendrochronologist at the California State University of Technology Humboldt, who led the new analysis. This means that rather than simply approaching a tree and collecting a single core, as is commonly done in dendrochronological studies, the researcher dons climbing gear and free-hangs his rope. This is because he climbed through and collected cores every 10 meters of him along the tree trunk.
fear of heights Redwoods tower 116 meters (380 feet) high.
He said he could spend most of his day simply roping a single tree and collecting cores. Steve SillettA botanist at Cal Tech Humboldt, he did a lot of climbing. Each core, 0.5 centimeters (0.2 inches) in diameter, was manually drilled using an instrument called a drill. Incremental Borer“This is hard physical work,” says Sillett. “By the end of the day, our arms are sore.”
To transport the core safely to the ground, the team put it in a hard case and put it in a drawstring bag. But taking the core out and putting it in the case is a delicate task, especially if the core is fragile, he says, Sillett. “Sometimes they fall, and it’s excruciating.”
wood puzzle
Carol led the analysis of the team’s approximately 6,000 cores. A series of growth rings was revealed from each cylindrical sample. Carroll’s first step was to cross-match sequences obtained at different heights from a single tree. Carroll said it was harder than he imagined. sequoia sequoia sempervirens It does not always grow uniformly along the entire vertical extent of the tree.
“I can’t imagine the complexity of the puzzle they had to put together.”
It is relatively common for these trees to lose their annual rings at some point. Evan Larson, a dendrochronologist at the University of Wisconsin-Platteville, was not involved in this study. Sequences from the same coastal redwood can have large differences in the number of rings, he said.
For each of the 278 trees sampled, Carroll used visual and computer-assisted matching to compare ring width patterns and determine the complete growth sequence. She identifies sequences of so-called marker years (tree rings that are characteristically thicker, thinner, or otherwise altered and correspond to independently dated events such as droughts and fires), allowing them to move forward or backward in time. A calendar year was assigned to each tree ring by counting.
In all, Carroll has amassed over 1.2 million rings. Keeping all these measurements accurate was definitely a huge undertaking. Brian BlackA dendrochronologist at the University of Arizona, Tucson, who was not involved in the study. “I can’t imagine the complexity of the puzzle they had to put together.”
Carroll then pieced together the growth sequences of different trees growing within a kilometer or so of each other. According to Carroll, it is most useful to compare trees growing in close geographical proximity because they experience similar climates, which are the primary drivers of ring growth. It is becoming
Carroll divided the team’s tree sample into 47 regions and created a tree-ring chronology for each region. These records range in length from 86 to 1,687 rings, with the oldest ring from a tree in the Santa Cruz Mountains dating to 328 AD. reported in annual ring chronology.
earthquake investigation
Coastal sequoias have long stood as sentinels of complex ecosystems shaped by fire, drought and fog. Many of these environmental factors can be recorded in tree rings, and redwoods can accordingly provide a record of long-term climate change, Larson said. More than half of the new chronology is at least 500 years old, Larson says, which is important in determining when certain environmental changes occurred. He “has the ability to extend perspective beyond human timescales.”
Carol and her colleagues are already planning to use one of the local chronologies to investigate the mysterious earthquake. The team samples wood from near the Harold Richardson Redwood Reserve in Sonoma County, California, to date earthquakes that occurred on the northern San Andreas Fault between the 17th century and her 19th century.
This earthquake was the last major event in San Andreas before the famous 1906 earthquake that devastated much of San Francisco. Ground shaking can cause trees to snap or bend, so researchers will sample and date the wood, looking for consistent patterns of damage that may have been caused by the earthquake.
—Katherine Cornay (@KatherineKornei), science writer
