10 Amazing Secrets from ‘The Hidden Life of Trees’

You don’t have to head to a museum to see an impressive work of art. Just go outside and look at the trees. Mother Nature’s masterful sculptures are right by the curb or the park bench, but they are so often and so easily overlooked. That’s just one of the reasons we love to feature trees on our outdoor scavenger hunts.

In Philadelphia’s Washington Square, we send hunters in search of the tree that grew from seeds that traveled into space and back with an Apollo mission. In another Washington Square in New York City’s Greenwich Village, our hunt points out the “Hangman’s Elm,” which legend (inaccurately) says helped execute criminals back in colonial times. On the Babson College campus outside of Boston, teams must locate an apple tree that descends from the very tree Isaac Newton sat under when falling fruit prompted his “eureka!” moment. Then there’s the historic Charter Oak on our hunt in Hartford, Connecticut, and an ancient mulberry tree outside a historic house on our Annapolis hunt, and…we could go on.

So imagine our delight when we discovered the best-selling book The Hidden Life of Trees: What They Feel, How They Communicate by Peter Wohlleben. We can’t wait to plunge into his new book, The Weather Detective: Rediscovering Nature’s Secret Signs, which was released this week. To give you a taste of the kind of fascinating facts he reveals, here are the ten coolest secrets we learned from Wohlleben about trees.

1. Trees help one another through a “wood-wide web.”

When you walk in the woods, there’s a network beneath your feet. Parent trees nourish their saplings through roots, and with the help of symbiotic fungi, roots connect neighboring trees to share nutrients and warnings about threats.

2. Apparently trees can count——and remember things.

How do trees know when to leaf out? How do they avoid getting faked out by premature bursts of warm weather? “They wait until a certain number of warm days have passed, and only then do they trust that all is well and classify the warm phase,” writes Wohlleben. They also count daylight hours. For example, beeches only begin growing once it is light for at least 13 hours a day. So not only can buds “see,” but if trees are counting days, they must also have a memory. Think about that the next time you break off a healthy branch.

3. “When trees are really thirsty, they begin to scream.”

At the ultrasonic level, that is. Scientists have recorded vibrations in the trunk when water flow is interrupted. “This is a purely mechanical event and it probably doesn’t mean anything,” says Wohlleben. “And yet?”

4. Trees need sleep.

When the leaves fall in autumn, it’s bedtime. “Sleep deprivation affects trees and people in much the same way: It is life-threatening,” explains Wohlleben. That’s why oaks and beeches won’t grow in year-round summer conditions inside your house. A study of oak trees in one American city found that four percent died due to exposure to nighttime lights.

5. When you see leaves, all that green is “waste light.” 

Photosynthesis makes use of all the wavelengths in the spectrum except green. So what you see is what the tree doesn’t want. Some of that reflected light suffuses the forest with a subdued green hue that has a relaxing effect on the human psyche.

6. Trees can taste the air——and insect saliva.

When under attack from pests, some trees can identify different insects by their saliva. The tree releases pheromones that warn other trees—and sometimes summon other insects that prey on the attacker. Here’s a nasty example: “Elms and pines call on small parasitic wasps that lay their eggs inside leaf-eating caterpillars.” You can imagine the gruesome outcome.

7. Some roots really get around.

Quaking aspens—which get their name from how the trees tremble in a breeze—send out roots to propagate more trees. Consider one overachiever: Over the course of thousands of years, one quaking aspen in Fishlake National Forest, Utah (above), has covered more than 100 acres with more than 40,000 trunks. Makes the tree in your front yard look lazy, right?

8. On average, each tree raises just one adult——if it’s lucky.

Trees are profligate with seeds because, statistically speaking, all but one is a goner. Consider this: In five years, one beech tree produces at least 30,000 beechnuts. Adulthood for one of them is 80 to 150 years away. Let’s say it reaches the age of 400. It will produce a total of some 1.8 million nuts, but odds are that just one will survive all the perils of the forest to develop into a full-grown tree. Jackpot!

9. The air in young pine forests is almost germ-free.

That’s thanks to phytoncides, released by the tree’s needles. The chemical has antibiotic properties. Add a pinch of crushed spruce or pine needles to a drop of water containing protozoa and they’ll be dead in less than a second. Basically, the trees disinfect their surroundings. The phytoncides also provide forests with a delectable scent on hot summer days.

10. A walk in the woods is good for you.

A Korean study of older women tracked their walks in forests and urban areas. Perhaps not surprisingly, their blood pressure, lung capacity and the elasticity of their arteries improved in the woods but not in the city. As Wohlleben puts it, “Every walk in the forest is like taking a shower in oxygen.” But only by day. Trees don’t photosynthesize at night, so they’re not exhaling oxygen through their leaves or needles then. Plus, that’s when the werewolves are out.

Tree enthusiast Bret Watson is the founder of Watson Adventures and author of many of the scavenger hunt questions featuring trees.