Redwoods: How Tall Can They Grow?

No existing species of tree can grow higher than 130 meters (427 feet).

So declares a Nature article by plant physiologist-ecologistGeorge W. Koch of Northern Arizona University and three colleagues from Humboldt State University in Arcata and Pepperdine University in Malibu.

The world’s tallest trees are California redwoods, technically known as Sequoia sempervirens. Until recently, some tree experts had theorized that the redwoods’ couldn’t exceed 120 meters (394 feet). But the theory clashed with historical legends of taller trees.

“There have been accounts of a Douglas fir tree that was measured early in last century and was 125 meters (410 feet) tall. It’s no longer standing,” Koch said in a phone interview. Also, folklore records redwoods and a tall- growing form of eucalyptus that approached 130 meters, supposedly in the Pacific Northwest and Australia, “but those are less trustworthy records,” he notes.

To reach the treetops at Humboldt Redwoods State Park, team member Stephen C. Sillett, a botanist at Humboldt State, shot arrows toward sturdy- looking branches about two-thirds of the way up a typical redwood tree. Attached to the arrows were ropes. Then the scientists climbed the ropes.

On their way up, they collected leaf samples. They also used instruments to measure height-related changes in water pressure and solar-driven photosynthetic activity.

As one ascends the redwoods, one ascends into another ecological world. Leaf sizes get smaller and smaller, as a result of the ever-greater difficulty faced by water as it squeezes through capillaries toward the treetops.

Several years ago, in independent research, Sillett and colleagues measured the tallest coastal redwood: 112.7 meters (370 feet) high. His measurement tools vary; they include a laser range finder and a weighted fiberglass tape that he drops from the treetop.

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