Peter Wohlleben’s “The Hidden Life of Trees”

Until recently I was quite sure that a broad difference between animals and plants was that animals, because they are mobile, readily interact with each other (flocking, pursuing, etc.) while plants, anchored to the ground, don’t do so because they can’t. Except to attract insect pollinators, plants, I thought, live a life of exquisite solo struggle, seeking only the sun and water.

I’ve been steadily learning how far off I was. German forester Peter Wohlleben’s popular book, The Hidden Life of Trees: What They Feel, How They Communicate, is the most compelling lesson yet.

Among his many descriptions of communication and mutual assistance is Wohlleben’s account of how trees defend not only themselves but also each other. Observers have noted, for example, that umbrella thorn acacias in the African savannah pumped toxins into their leaves when they felt giraffes nibbling on them. “The giraffes got the message and moved on to other trees in the vicinity. But did they move on to trees close by? No, for the time being, they walked right by a few trees and resumed their meal only when they had moved about 100 yards away.” They passed by the nearest trees because the trees being nibbled, in addition to pumping a repellent, “gave off a warning gas that signaled to neighboring trees that a crisis was at hand.” The giraffes knew these trees would not taste any better and kept walking.

hidden life of trees (pri.org)

pre.org

Many trees also have the ability to call in the air force. Reacting to bites from hostile insects, such trees emit scents that attract predators that devour the pests. “For example, elms and pines call on small parasite wasps that lay their eggs inside leaf-eating caterpillars.” The growing larvae devour the caterpillars from the inside.

The book brims with information and appreciations of this kind. Three more examples:

  • Trees that spend their lives in the forest fare much better than trees raised in one place and then transplanted to the forest. “Because their roots are irreparably damaged,…they seem almost incapable of networking with one another.” Like “street kids,” they “behave like loners and suffer from their isolation.”
  • Time for trees is slow and long. Internally, they, like animals, send alerts to parts of their body via chemicals and electrical impulses. But in a tree the electrical impulses move only about a third of an inch per second. (In our bodies, pain signals move  through our nerves about two feet per second, muscle impulses a hundred times faster.) No wonder it seems to us that plants are unresponsive.
  • Conifers (evergreens) “keep all their green finery on their branches” throughout the winter and have been doing so for 270 million years. Then deciduous (leaf-bearing) trees came along 100 million years ago, growing and discarding annually millions of delicate green solar panels. Was this an improvement? Why go to all that trouble? Wohlleben asks. Because “By discarding their leaves, they avoid a critical force—winter storms.” Between high winds, muddy soil, and a surface area equivalent to that of a large sailboat, tall evergreens take a battering in European winters. Growing and then dropping their huge surface area every year proved well worth while for the leafy new comers.

Wohlleben’s liberal use of human descriptors to explain the actions of trees delights many readers and annoys others. Andrea Wulf, in her review of the book, has both reactions.

I’m usually not keen on anthropomorphizing nature—and here trees are “nursing their babies” and having “a long, leisurely breakfast in the sun” while…fungus mushrooms are “rascals” who steal sugar and nutrients. These cutesy expressions make me cringe….But I have to admit that Wohlleben pulls it off—most of the time—because he sticks with scientific research and has a knack for making complex biology simple and thoroughly enjoyable.

I agree. While the vocabulary may bestow on trees a dignity and affection that we usually reserve for our own kind, it is scientists’ growing understanding of trees that creates the real story here. At a time of rapid environmental change, the book is as fascinating a revelation as one could ask for that life is even more intricate and purposeful than we knew.

The Homely Truth About the Shortest Day

We passed the shortest day of the year last week. It’s the annual drama of encroaching darkness turning to growing light, the grand rebirth, the celestial, uplifting reminder that in any sphere of life, the gloom gives way to brightness.

I’ve always imagined the event as accompanied by an elegant symmetry. I thought that the darkness closed in evenly from both sides, that the sun rose a little later each morning and set a little earlier until the shortest day on December 21st, when the process neatly reversed at both ends of the day. The sequence, I thought, between early December and early January had the shape of a tall hourglass. The left “sunrise” side sloped in to the right during most of December and the right “sunset” side sloped left, each changing by a minute or two each day. On December 21st, they met at the narrow waist and reversed direction.

scienceblogs.com

scienceblogs.com

Well, it doesn’t work that way. Changes in sunrise and sunset times aren’t in synch. The sun doesn’t neatly rise later each morning until the 21st and then reverse course. It keeps rising later and later well beyond the 21st, past Christmas and into the first week of January. Imagine the left side of the hourglass sloping down and right until it’s well below the waist.

The timing of sunsets changes in the opposite way. Sunsets change direction, from happening earlier to happening later, about a week before the shortest day. Imagine the right side of the hour glass sloping inward not all the way down to the waist but only part way. Such an hourglass would have a weird, uneven tube descending from the upper left to lower right. It isn’t until early January that both sides would be moving apart from each other again.

The shortest day is the shortest only because the speed of the changes in the times of rising and setting vary from day to day. In early December, the sun rises later by a sizable couple of minutes every day, while sunset drags on at almost the same time, so the length of daylight shrinks until the 21st. After that, the changes in sunrise slow way down while it is sunset’s turn to pick up the pace, getting rapidly later (by about 7 minutes between the 21st and New Year’s Eve in New York) and lengthening the day.

So the shortest day grows out of a ragged process, not the aligned and symmetrical one we thought we were seeing. The universe spins in ways that we don’t or can’t grasp in detail, but we pull the meanings that we need from our approximations anyway.