Forest Giant

A tree-climbing scientist and his team have learned surprising new facts about giant sequoias by measuring them inch by inch.

It’s not quite the largest tree on Earth. It’s the second largest. Recent research by scientist Steve Sillett of Humboldt State University and his colleagues has confirmed that the President ranks number two among all big trees that have ever been measured—and Sillett’s team has measured quite a few. It doesn’t stand so tall as the tallest of coast redwoods or of Eucalyptus regnans in Australia, but height isn’t everything; it’s far more massive than any coast redwood or eucalypt. Its dead spire, blasted by lightning, rises to 247 feet. Its four great limbs, each as big as a sizable tree, elbow outward from the trunk around halfway up, billowing into a thick crown like a mushroom cloud flattening against the sky. Although its trunk isn’t quite so bulky as that of the largest giant, the General Sherman, its crown is fuller than the Sherman’s. The President holds nearly two billion leaves.

Trees grow tall and wide-crowned as a measure of competition with other trees, racing upward, reaching outward for sunlight and water. And a tree doesn’t stop getting larger—as a terrestrial mammal does, or a bird, their size constrained by gravity—once it’s sexually mature. A tree too is constrained by gravity, but not in the same way as a condor or a giraffe. It doesn’t need to locomote, and it fortifies its structure by continually adding more wood. Given the constant imperative of seeking resources from the sky and the soil, and with sufficient time, a tree can become huge and then keep growing. Giant sequoias are gigantic because they are very, very old.

They are so old because they have survived all the threats that could have killed them. They’re too strong to be knocked over by wind. Their heartwood and bark are infused with tannic acids and other chemicals that protect against fungal rot. Wood-boring beetles hardly faze them. Their thick bark is flame resistant. Ground fires, in fact, are good for sequoia populations, burning away competitors, opening sequoia cones, allowing sequoia seedlings to get started amid the sunlight and nurturing ash. Lightning hurts the big adults but usually doesn’t kill them. So they grow older and bigger across the millennia.

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