The oak tree in my yard appears to be deaf, dumb and solitary. But it’s probably not. Indeed, it may well be part of a local network of oaks that communicate more frequently than I do with my human neighbors: a “wood wide web” of sorts.
If that sounds like a fairy tale, then I recommend reading Peter Wohlleben’s The Hidden Life of Trees: What They Feel, How They Communicate―Discoveries from A Secret World. This post covers the first four chapters of the book.
Keeping the Ancient One Alive
Wohlleben, a German forester, begins his book with the discovery of an ancient tree stump that was still alive hundreds of years after the beech itself had been cut down. He was stunned, knowing that the stump should have long since disintegrated into humus. How could it still be alive?
There was only one possible answer: the beech trees around it were pumping sugar to the stump to keep it alive. This is just one piece of evidence supporting the modern finding that, within natural forests, trees of the same species are interconnected to one another via their root systems. They share resources because they are stronger as a collective than as individuals.
The collectivist nature of trees shows up in various studies. For example, the umbrella thorn acacias on the African savannah alert one another to danger via their sense of smell.
Wait, what? Trees smell other trees? In this case, yes. When giraffes start eating the leaves of an acacia, the tree tries to protect itself by “pumping toxic substances into their leaves,” apparently making the leaves bitter and driving the giraffes away. Even more remarkably, though, the same harassed tree vents ethylene to warn local acacias that the hungry giraffes are in the neighborhood. Those trees somehow smell the warning and start pumping their own toxins. So, the stand of trees is safer collectively than as individuals.
The Enemy of My Enemy
But it gets even stranger. You and I have nervous systems based on electrical impulses. So do trees. It’s true that those impulses travel more slowly (a plant signal travels at about a third of an inch per minute). But they can react in very canny ways.
For example, trees can taste the saliva of the insects eating them to identify their species. Armed with that knowledge, then can then send out pheromones to bring in other creatures who will eat those harassing insects. “For example,” writes Wohlleben, “elms and pines call on small parasitic wasps that lay their eggs inside leaf-eating caterpillars.”
But trees don’t only call in the troops from other species. They can fight on their own as well, as the acacias do. My oak tree, for example, can produce toxic tannins in its leaves and bark in order to kill or at least chase away hungry insects.
The Wood Wide Web
Trees don’t only communicate by sending chemical signals through the air. They also send signals through the fungal networks that grow around the tips of their root systems. “Surprisingly,” Wohlleben writes, “the news bulletins are sent via the roots not only by means of chemical compounds but also by means of electrical impulses.”
These signal-sending fungi are often dense in the soil, with a single teaspoon containing miles of hyphae if the tendrils were were laid end to end. This “wood wide web” connects trees and allows them to share information about predators, drought and other dangers.
My Dumb Garden
Humans have typically bred plants for characteristics other than communication, so our agricultural plants have tended to be silent, hindering their ability to warn one another of mutual enemies. This means they (and we) rely on pesticides for protection, which leads to a wide range of other problems that we might be able to avoid, in part, if we could breed more talkativeness back into them.
Remember the ancient beech tree stump that was kept alive by its neighbors hundreds of years after the tree itself had been cut down? Well, this is apparently because wild trees have a kind of income distribution system that shares resources equally through the forest.
[E]ach tree experiences different growing conditions; therefore, each tree grows more quickly or slowly and produces more or less sugar or wood, and thus you would expect every tree to be photosynthesizing at a different rate. And that’s what makes the research so astounding. The rate of photosynthesis is the same for all the trees. The trees, it seems, are equalizing differences between the strong and the weak….This equalization is taking place underground through the roots [and fungi]….Their enormous networks act as gigantic redistribution mechanisms.
In short, the networks make it easier for the forest as a whole to thrive, thereby better safeguarding the lives of the individual trees within. (That’s not to say they don’t also compete viciously for the sunshine at times, but we’ll save that for a future post.)
War on the Woodland Creatures
Being a nut-producing deciduous tree in a world of browsers can be brutal. After all, boar, deer and other woodland creatures love acorns, beech nuts and the like. If the trees bloom en masse at a time when there’s been a population boom among the browsers, then the nuts all get eaten and the trees can’t reproduce. But if the trees wait till the browsers are scarce, then they’ll have much greater reproductive success.
So, what do the trees do? Well, they sometimes wait several years between blooms, basically starving out the browsers (and encouraging them to have fewer offspring) until their numbers go down. Only then do they go all fruitfully bacchanalia, throwing down so many nuts and seeds that the deer and boar can’t get to them all.
Thus there is this boom-bust cycle in forests. Trees may seems like gentle giants, but they know how to play rough with the browsers when necessary.
Addendum: Live by the Network, Die by the Network
Some fungi are crucial for allowing trees to communicate with one another, but forest fungi are not all created equally. Nor are they all on friendly terms with trees. In fact, the world’s largest organism is a fungus growing in the Malheur National Forest.
The honey mushroom (aka, Armillaria ostoyae) occupies a total area of 2,385 acres and mostly lives about a yard underground in the form of mycelia, a network of fungal threads or hyphae. And it’s not just large, it’s ancient: least 2,400 years old maybe as as much as 8,650 years old.
The honey mushroom is killing vast numbers of the trees in the Malheur Forest. All of which goes to show that nothing in nature is simple. We may think of fungi and trees as embracing on another in a giant display of networked kumbaya, but there’s war here as well. It all comes down to particulars.
Featured image: Avenue of Oaks at Boone Hall in Charleston, South Carolina by Brian Stansberry. See https://commons.wikimedia.org/wiki/File:Boone-hall-avenue-of-oaks-sc1.jpg