Fraternization Under the Forest Floor

In my first post on Peter Wohlleben’s The Hidden Life of Trees, I wrote a bit about the how certain hyphae–that is, the branching filaments that make up the mycelium of a fungi–play a key role in establishing the “wood wide web.” But perhaps you were left wondering, “Okay, but what’s in for the fungi?”

The Enlighted Entrepreneurship of Fungus

As it turns out, a lot. The fungi definitely take their cut of the sugar and other carbohydrates produced by trees. Indeed, they can take as much as a third of a tree’s total food production for services rendered. A third!

The IRS has got nothing on the fungi.

So, what do the trees get in return? Well, as we previously noted, they extend the reach of tree roots and allow trees to share not only nutrients but also information with one another. Let’s face it, that’s pretty good service. It’s as if our Internet provider was not only letting us exchange information but also allowing us to directly send food and water to one another.

But, as the Ronco people used to say, “And that’s not all!”

The beneficial fungi also provide certain medical benefits. Not only do they filter out poisonous heavy metals, they ward off bacteria and the more destructive types of brethren fungi.

But these tree-loving fungi are not dedicated to just one species of tree. They play the field, willing to connect trees of different species. Wohlleben writes, “Although many species of tree fight each other mercilessly above ground and even try to crowd out each other’s root systems, the fungi that populate them seem to be intent on compromise.”

In a way, the fungi are like a huge retail chain (think Amazon), helping many companies because betting on just one corporation could be disastrous if that corporation failed. Similarly, the fungi do not want to bet on just one species of tree because if some plague takes out that species, then they their fates are tied only that failing species. If a beech tree complains to that it’s local fungi should not also be helping their competitors the oaks, you can almost hear the fungi say, “Sorry there Beech boy, it’s not personal, it’s business.”

Plumbing the Mysteries of Trees

Not only don’t we fully grasp the complexities of trees, we don’t even understand a lot of the basics. One of those basics is plumbing. That is, how do trees pump water all the way from their roots to their crowns?

Wohlleben discusses two primary theories. First, there’s capillary action. Wikipedia defines the action this way:

[T]he process of a liquid flowing in a narrow space without the assistance of, or even in opposition to, any external forces like gravity. The effect can be seen in the drawing up of liquids between the hairs of a paint-brush, in a thin tube, in porous materials such as paper and plaster, in some non-porous materials such as sand and liquefied carbon fiber, or in a biological cell. It occurs because of intermolecular forces between the liquid and surrounding solid surfaces. If the diameter of the tube is sufficiently small, then the combination of surface tension (which is caused by cohesion within the liquid) and adhesive forces between the liquid and container wall act to propel the liquid.

Here’s how I think of it: when you put water in a narrow vessel, the water itself stands above the lip of the vessel. So, when you fill a glass of water to the brim, the water actually stands slightly above the rim of the glass due to capillary action. The narrower the vessel, the higher it stands.

Although I’ve noticed this before, I’ve never thought much about it. However, this action accounts for some of the rise of water up the trunk of a tree. How much? Wohlleben says 3 feet in a 300 foot tree. In other words, more than you might think but not all that much.

The second way trees pump water is transpiration. Wohlleben describes it thus:

In the warmer part of the year, leaves and needles transpire by steadily breathing out water vapor. In the case of a mature beech, the tree exhales hundreds of gallons of water a day. This exhalation causes suction, which pulls a constant supply of water up through the transportation pathways in the tree.

So, the tree uses suction, the same principle by which we drink our juice boxes. Which is very cool!

There’s just one problem with this transpiration idea. It doesn’t explain the mysterious rise of water in trees before the leaves emerge. In fact, water pressure is highest in trees before leaves open in the spring!

So, we can glibly toss around terms such as capillary action and transpiration, but they alone can’t account for what trees are doing in the real world. And, if we can’t even account for basic plumbing in trees, imagine how much else we’re missing.

Skin in the Losing Game of Life

Bark is the skin of trees. Like our skin, tree bark is constantly being shed. As with our skin, bark holds in life-giving water and protects a tree’s inner organs from the deadly world outside. As with our skin, bark wrinkles as the trees age.

The wrinkles aren’t the only things we share with trees. Like us, trees actually start to bald and shrink a bit as they get old. And, as with us, they finally succumb to entropy, and their bark begins to fail.

When it does, the non-beneficial types of fungi help bring about their demise. Wohlleben writes:

Small moist wounds have become portals for fungi to enter. The fungi advertise their triumphant advance through the tree by displaying magnificent fruiting bodies that jut out from the trunk in the shape of semicircular saucers that grow larger with each passing year…Then one day it’s all over. The truck snaps and the tree’s life it at an end.

And so the tree dies and eventually becomes part of the forest floor, feeding the roots of its competitors and children. Meanwhile, the fraternizing fungi below continue their work, taking in the big picture, ultimately seeing the forest for the trees.

It’s Not Easy Being Green

This is my second post on The Hidden Life of Trees, by Peter Wohlleben. It more or less covers chapters 5 through 8, though I also get sidetracked by discussions of Plato and anthropomorphism, topics (no doubt wisely) not covered in the book.

A Last Hurrah

Even without fire, extreme drought is deadly to trees. Their defenses run down and they become highly susceptible to insect attacks.

What’s surprising, however, is how they react. Under these pressures many bloom the following year. Wohlleben writes:

We know from times of high forest mortality that is usually the particularly battered individuals that burst into bloom. If they die, their genetic legacy might disappear, and so they probably want to reproduce right away to make sure it continues.

Even if it makes a kind of Darwinian sense, it seems oddly desperate or even poetic. It has a whole “one last hurrah” vibe to it. But perhaps I’m anthropomorphizing. If so, I’m in good company.

Arboreal Anthropomorphism

A friend of mine said, correctly I think, that Wohlleben tends to anthropomorphize in his book. When he attributes desire to a tree, he seems to be indicating that the tree is using emotion or logic to determine its next steps. In other words, he makes the tree sound as if it’s a human being.

Personally, however, I’m fine with this because trying to “write around” this issue would make his work read like a text book, replete with passive voice, wonky syntax and sterile language, all in an effort not to attribute human characteristics to trees. That strikes as me unnecessary for two reasons. First, we all know that trees aren’t human beings and that this bit of writerly shorthand is not necessarily to be taken literally.

Second, and perhaps more important, we still don’t understand trees. This is, in fact, one of the key themes of the book. We don’t know how the trees are able to do all the things they do. In many cases, we literally don’t know the degree to which they are and are not like us. In the absence of such knowledge, I don’t think we should get hung up on these issues. Save it for the scientific papers.

So, with those caveats in place, let’s anthropomorphize some more.

Tough Tree Love

Trees are very controlling parents. When a young tree takes root beneath the canopy of a parent tree, it is literally overshadowed for decades and often longer. Wohlleben notes that only 3% of available light gets through to the young tree, causing it to grow very, very slowly. From our perspective, this sounds like an extended juvenilization and a dysfunctional degree of tough love.

But it makes sense to the trees (or, at least, many species of them). Because of the slow growth of the juvenile trees, their “inner woody cells are tiny and contain almost no air” and this makes them more flexible, resilient, and resistant to fungus, insects and other threats. That which does not kill a tree apparently makes it stronger. Nietzsche would approve.

Plato’s Trees

You may remember that the Greek philosopher Plato had a theory of forms. This posits that only ideal forms encapsulate the true and essential nature of things whereas individual cases of those forms cannot live up that essential nature.

Referring to the theory of forms, Wikipedia explains, “We recognize a tree, for instance, even though its physical form may be most untree-like. The tree-like nature of a tree is therefore independent of its physical form.”

But maybe it’s the other way around. That is, maybe individual trees do not reflect the ideal tree in some imperfect form. Maybe the ideal tree stems from the very real needs of individual trees. Wohlleben writes:

This is what a mature, well-behaved deciduous tree looks like. It has a ramrod-straight trunk with a regular, orderly arrangement of wood fibers. The roots stretch out evenly in all directions and reach down into the earth under the tree….[T]here is a good reason for this ideal appearance: stability….Evenly formed trees absorb the shock of buffeting forces, using their shape to direct and divide these forces evenly throughout the structure.

Of course, not all trees wind up looking like the ideal, but they tend to have a better chance of a long and productive life if they do. So, evolution not only shapes the trees but our very ideal of trees–and perhaps even our inherited sense of what is and is not beautiful in the natural world.

The School of Hard Knots

Trees adapt. Or do they learn? What’s the difference?

I’m not going to take a stand on the question, but I will say that they definitely adapt and sure as heck seem to learn.

And its not just trees but other plant kin as well. Let’s start with mimosas. You may have experienced them before. They’re the plants that close their feathery little leaves when you touch them. I still remember the first time I encountered them because they seemed like some hybrid between a plant and animal. But, no, they’re just plants that react a bit more quickly to stimuli.

Dr. Monica Gagliano wanted to see if mimosas can learn, so she “designed an experiment where individual drops of water fell on the plants foliage at regular intervals.” At first, the leaves closed up whenever the drops hit, but then the plants determined that the water wasn’t going to harm them and so remained open even when droplets fell.

Is this learning? Maybe. But it gets more interesting. When Gagliano checked again weeks later, the plants somehow remembered their lesson from weeks before and didn’t close up when the droplets fell. If this isn’t learning, it’s hard to know what else to call it. Now how a brainless plant learns is not clear, but that’s for a different post.

For now, let’s go back to trees. It turns out some trees are spendthrifts and some are frugal when it comes to water. The spendthrifts are the ones with easy access to water and they use a whole lot of it. But they are also the ones hit hardest by droughts because they don’t know how to conserve. They can suffer badly as their wood dries out and this can result in major tears in their bark, opening them up to all kinds of ills such as insects and fungi.

But they can learn to be thriftier. Wohlleben writes that such tree often “takes the lesson to heart, and from then out it will stick with [a] new thrifty behavior, even when the ground has plenty of moisture–after all, you never know!”

So, can a tree be redeemed, having learned from it’s improvident ways? Perhaps so. Maybe there’s hope for all of us.

Featured image: Beech tree with frost crack bark damage, Stacklawhill. Rosser1954.,_Stacklawhill,_North_Ayrshire.jpg

The Wood Wide Net and Socialist Trees

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.

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.

Talkative Trees

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.

Socialist Forests

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.

Wohlleben writes:

[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