Some trees may ‘social distance’ to avoid disease


In some ways, crown shyness is the arboreal version of social distancing, says Meg Lowman, a forest canopy biologist and director of the TREE Foundation. “The minute you start keeping plants from physically touching each other, you can increase productivity,” she says. “That’s the beauty of isolation … The tree is really safeguarding its own health.”

Regardless of how crown shyness occurs, the separation likely comes with benefits. “Leaves are like a tree’s most expensive diamonds—you want to protect them at all costs,” Lowman says. “If a whole bunch get bumped off, that’s a terrible disaster for the tree.”

Sparser foliage could also help sunlight reach forest floors, nurturing the ground-dwelling plants and animals that in turn support arboreal life. Putz thinks the gaps may even help trees avoid invasive, woody vines called lianas—which are common in tropical and temperate forests around the world—or buffer the plants against disease-causing microbes and flightless insects that use canopies as conduits. (Some germs and bugs could still theoretically make the hop when trees box in the breeze.)

Many of these possible advantages, however, have yet to be conclusively linked to crown shyness. Forest canopies—the tops of some of the world’s tallest plants—aren’t easy to study, says Lowman, a self-described “arbonaut” and one of the few scientists who has made a career studying canopies. Examining the tops of trees requires quite a bit of climbing, balance, and bravery. “The limiting factor is our inability to deal with gravity to get to those places,” she says.

Still, ignoring the canopy of a tree is like trying to understand the human body from only the waist down, Lowman says. The crowns of trees teem with life—and much of this biodiversity may still be undiscovered, especially in the tropics.

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