Cooperation Makes the Forest

The really big takeaway from modern research on trees is simple: trees in an old-growth forest cooperate. Far from being individuals seeking only their own success, trees cooperate not only with others of their own species but with those of different species too, and also with the fungi that, though often feeding upon them and debilitating them, also cooperate with trees to the mutual success of both. In order to do this, of course, trees must communicate in some way that has long been invisible to us, but is now becoming more commonly known. This ‘secret life of trees’ forms the basis for two books I’ve read recently, one a novel: The Overstoryby Richard Powers, and the other a nonfiction account by a German forester, Peter Wohlleben, who wrote The Hidden Life of Trees. Together with the pioneering research of Suzanne Simard about plant-fungi communication (Simard writes a note to Wohlleben’s book and is the model for the fictional scientist, Patricia Westerford, Powell creates in The Overstory), these two books change one’s outlook on what a tree is, and why preserving old-growth forests is more important in more ways than we ever could have imagined. 

            To begin with The Overstory, Powers writes a novel dramatizing the awakening to the importance of trees by several characters, most of whom he brings together as activists committed to saving old-growth forests in the Pacific Northwest. These actions are based on the activism of well-known ‘tree-huggers’ like Julia Butterfly Hill and others, but Powers has them take even more radical action, perhaps based on the Weathermen—that is, setting fire to buildings. All of them stop this activity when one of their number is critically injured in a fire, but their commitment makes the point: humans are latecomers to life, owe much of their sustenance and even genes to trees, and with logging are destroying the very means of maintaining life on the planet. For me, the most compelling character in Powers’ fictionalized account was scientist Patricia Westerford, so much so that I was driven to search out the character upon whom she was based. That brought me to Dr. Suzanne Simard, who has several videos wherein she makes the case for her major research finding, tree communication. 

            Simard is a professor of Forest Ecology at the University of British Columbia, Vancouver. In her note at the end of Wohlleben’s book, she writes that her doctoral research led her, in 1992, to some amazing discoveries regarding the mutual relationship between paper birches, a deciduous tree, and their conifer neighbors. The birches seemed to be feeding the soil and helping Douglas firs nearby. Simard’s question was exactly how and why they were doing this. Here is what she writes:

            In pulling back the forest floor using microscopic and genetic tools, I discovered that the vast belowground mycelial network was a bustling community of mycorrhizal fungal species. These fungi are mutualistic. They connect the trees with the soil in a market exchange of carbon and nutrients and link the roots of the paper birches and Douglas firs in a busy, cooperative Internet. When the interwoven birches and firs were spiked with stable and radioactive isotopes, I could see, using mass spectrometers and scintillation counters, carbon being transmitted back and forth between the trees, like neurotransmitters firing in our own neural networks. The trees were communicating through the web! (Wohlleben, 248).

Simard went on to discover the dynamics of the synergy between the two tree species: “the firs were getting morephotosynthetic carbon from the birches than they were giving,” which meant that the birches were spurring the growth of the firs, as if they were caring for them; and the firs, in turn, were being “mothers” to the birches as well, depending on the season. There was, in short, a mutual exchange between two apparently rivalrous species, mediated by fungal mycelia, thus making a forest. In her paper describing this, published in Naturein 1997, the term “wood-wide web” was introduced. Many scholars have now built on Simard’s research about belowground communication between trees, mapping and monitoring the subtleties of communication that goes on in an ostensibly “silent” forest to the enhancement of the mutual health of all. As she puts it, “these discoveries have transformed our understanding of trees from competitive crusaders of the self to members of a connected, relating, communicating system” (249).  

            This becomes the essence of what Peter Wohlleben describes for us in The Hidden Life of Trees. A forest is a community. That is, an intact forest that is allowed to grow on its own, without the interference of humans (who think they are helping forests by thinning them out but are really hindering them), seems to know what it is doing, and to act for the good of the whole. The deep humus soil, enriched constantly by dead and dying trees, and inhabited by an astonishing array of life forms (“There are more life forms in a handful of forest soil than there are people on the planet” (86), is really the lifeblood of this immense life-fostering system. When it is disturbed and compacted by huge logging machines and cleared by ignorant humans, it is crippled. This is why, for example, trees in urban neighborhoods topple over so easily in windstorms: the roots, which are the brains and anchor of the tree, are limited from growing by concrete and by compacted soil; without their normal extended root support, trees topple over in strong winds. What’s even more astonishing and sad is the fact that while trees in intact forests carry on an active conversation via several modes of communication, trees in monocultural plantations (which we are assured replaces all the old-growth trees we use for lumber) are spaced in such a way that communication is silenced. As Wohlleben puts it, “Thanks to selective breeding, our cultivated plants (including trees planted for lumber) have, for the most part, lost their ability to communicate above or below ground—you could say they are deaf and dumb” (11—emphasis added). 

            Wohlleben gives us many instances of exactly how and why trees communicate. First and foremost is to create the ecosystem of the forest, which “moderates extremes of heat and cold, stores a great deal of water, and generates a great deal of humidity” (4). In such an environment, trees are our elders, living, through cooperation, to be hundreds of years old and surviving even regular forest fires. Needless to say, when forests are cleared or ‘thinned,’ that ecosystem, and life itself, is interrupted. But if, on the other hand, trees are allowed to live and learn (yes, trees have been proven to learn from experience and store that learning, probably in their root systems), they can perform feats such as those found among the thorn acacias of Africa. Scientists discovered many years ago that somehow these acacias were able to discourage giraffes from feeding on them and their neighbors. Upon investigation, they discovered two things: first, as soon as the trees ‘felt’ giraffes munching on their leaves, they started to “pump toxic substances into their leaves to rid themselves of the large herbivores” (this ability of plants to create almost endless varieties of chemicals is a cause for wonder, not to mention gratitude) (7). But this was only the beginning; the acacias being eaten also “gave off a warning gas (specifically ethylene) that signaled to neighboring trees of the same species that a crisis was at hand,” and instantly the warned trees also pumped toxins into theirleaves to protect themselves! In short, while we used to think that only animals or birds could warn their relatives of coming danger (vocally), we now know that trees do the very same thing—only employing systems that escape our senses. 

            One reason for our insensitivity, of course, is that much of the communication between trees takes place below ground. Here is where that mycelial network comes in. Since they cannot photosynthesize as trees do, fungi bargain with their specific trees: the fungi spread their mycelia throughout the tree roots, greatly increasing the root surface to suck up more water and nutrients. As Wohlleben points out, scientists find “twice the amount of life-giving nitrogen and phosphorus in plants that cooperate with fungal partners than in plants using their roots alone” (50). In return, the fungi get the sugar and other carbohydrates they need (from the tree’s photosynthesis) by growing into the tree’s root hairs, so that up to a third of the tree’s total production comes to them. This is costly for a tree (and each tree seems to have its appropriate mycelium with which to cooperate), but it apparently pays off in better nutrients, in the communication mentioned above, and also in the trick the fungi have to filter out heavy metals (damaging to trees) and bacteria that would otherwise feast on the tree. In short, this is a kind of symbiosis that is widespread in nature but which many human societies (or parts of them such as robber barons and bankers) seem to have forgotten. 

            One other benefit of trees (among the hundreds cited by Wohlleben) deserves mention. Trees, especially coastal rainforests, play an important role in how rainfall is used and distributed on the land-locked portion of continents. Part of every rain is intercepted by the huge coastal forest canopy formed by the tree crowns. Wohlleben writes that “each summer, trees use up to 8,500 cubic yards of water per square mile, which they release into the air through transpiration” (106). This tree-created water vapor then actually forms new cloudsthat travel farther inland than the average of 400 miles for typical ocean-driven storms, to release their rain. In other words, coastal forests amplify the life-giving precipitation from oceans and spread it far into the interior flatlands—the lands that in North America chiefly depend on this rain for farming. When these coastal forests are destroyed or dry out due to clear-cutting or thinning (as is already happening in Brazil, and as lumber companies have been doing in the Pacific Northwest), this life-giving system falls apart. Because of their moisture-preserving capacity (coniferous forests in the Northern Hemisphere also give off terpenes—whose molecules, giving moisture a place to condense, create clouds that are twice as thick), such forests even play a part in slowing down climate change. Of course, this is of no interest to the lumber predators and climate deniers now holding sway, but very soon the real price of this ignorance will become all too apparent. And finally, trees actually disinfect their surroundings through the release of phytoncides, chemicals with antibiotic properties they release to fight off bacteria. This makes the air in pine forests almost germ-free, perhaps one reason people find being in such forests so refreshing. 

            In sum, as many of our primary myths and legends suggest, trees are our forebears, the source of much of our DNA, our cells, our rain, our communication systems, our structure, our nutrition. The next time you think to cut down a ‘dumb’ tree, therefore, or hear about idiot legislation to make it easier to ‘harvest’ what’s left of our national forests, you might want to think again. You might want to pay homage to your parent, and see if you can get others to do the same—that is, to cooperate both within and between species—before it’s really too late. 

Lawrence DiStasi