Why Tropical Trees Don’t Have Rings | Kirk Johnson
About The Episode
Growth rings on trees can measure time, allowing scientists to date things from the deep past. But, paleobotantist Dr. Kirk Johnson explains why, in the tropics, some trees have no rings.
For more, check out the extended interview with Kirk Johnson.
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Kirk: A typical age of a tree is about the same age as a person. A typical tree lasts about 60 or 70 years, but some kinds of trees last thousands of years, like the bristlecone pines go back like 4,000 years. So they're good at telling times. They're good at telling time and human kind of stories. And we often use trees with growth rings to tell us about archeological sites because there's a thing known as dendrochronology, or using tree rings to measure time. It's one of the many ways we measure time, back in the past. But if you go to the tropical rainforest and cut a tree down, it has no rings.
Hakeem: What?
Kirk: Yeah, because there's no seasons. A ring is when the tree grows slowly. So it's like tree rings are something that's very familiar if you live in a temperate region, but if you go to the tropics and you saw a tree down, it's like, "Huh? Looks like butter."
Hakeem: It's ringless.
Kirk: Yeah. And so, in the tropics, if you want to measure how old the tree is, you can't count the rings. You have to watch it grow.