TEN YEARS AGO this week, Hurricane Katrina ripped through New Orleans and the Gulf Coast, bringing floods and gale-force winds that devastated the region and displaced more than a million people. But New Orleans’ live oaks were surprisingly resilient, as biologist Janine Benyus describes in our first episode of a new video series on biomimicry,Think Like a Tree.
As the tallest living things on earth, trees have developed strategies to protect themselves against threats to their leaved towers. In the process, they’ve “managed to solve daunting problems of engineering,” says Steven Vogel, a Duke biologist who studies the ways organisms structure themselves in moving fluids.
Take the beating a tree gets from a hurricane. Gale force winds hammer trees with a dynamic collection of blows, which unleashes “a suite of mechanical problems that would give an engineer nightmares,” Vogel says. Beyond withstanding high wind speeds, trees need to deal with wind acceleration and the air’s “throw weight”—its mass, basically. Calms between gusts can be damaging, too, as the tree rebounds and sways, potentially building up heavy loads on branches and roots. Not to mention the litany of other environmental factors that come into play during a storm: precipitation levels, soil conditions, the state of the surrounding trees.
So, what’s a tree to do? Leaves that work great for photosynthesizing become liabilities in high wind, Vogel says, where they act like little sails with a lot of drag. So in strong, 40 mph winds, the leaves of trees like maple, poplar, and holly will reconfigure into more aerodynamic shapes: curling up into little tubes, clumping together into cones, or flattening to reduce drag. And strong root systems serve as a countermeasure to the drag of the leaves and the wind’s sideways force.
Trees might be silent, brilliant engineers, but Vogel cautions that they may not be the best candidates for biomimicry. Trees operate under certain constraints—they grow all their own material, which takes energy that could be spent on other needs like reproduction. “Nature usually builds to a design criterion of adequate strength,” Vogel says, and that means maximizing whatever will keep the population going. If one tree goes down, that’s okay as long as most of them survive. But we build our cell towers and skyscrapers much more sturdily than they usually need to be, because we want them to work all the time. And we can account for that, Vogel says, thanks to modern engineering. So we’ll stick with our steel beams for now.
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