Sustainability and the Hidden Life of Trees

Beech tree forest, central Europe. Courtesy Wikimedia Commons

   By now many readers of this blog will have sat down with Peter Wollheben’s remarkable best-seller, The Hidden Life of Trees. Wollheben, a German forester, writes about forest sustainability, but there are takeaways for musical and cultural sustainability as well. Indeed, one of his major points is that trees have a kind of social and cultural life together. The author anthropomorphizes trees to an extent that bothers me; he attributes emotions and feelings to them, for example, as well as intentions and agency in ways that are striking. Nevertheless, he makes a convincing case that trees in a forest comprise an interactive community.
    In his first career, Wollheben was a professional forester, and managed a forest for commercial interests. In central Europe, as in many parts of the US, planned forests are planted (or replanted) with trees evenly spaced (or thinned to give them space) so they will grow fast for a quick harvest by large, efficient machines. Although he doesn’t specify, we infer that the forests he worked in were coniferous, with spruce trees the favored commercial species. At some point, he stopped managing commercial enterprises and instead began to manage an old-growth forest chiefly of beech trees, not for harvest but for preservation for the community nearby.
    When he began doing so, he observed that the beech forest (which had been growing for many decades without much human interference) was much different than the commercial forests he managed. The trees were much closer together—too close, in terms of the forestry management practices he’d learned—and yet they grew better, straighter trunks, and they grew more slowly and to a ripe old age: hundreds of years. It took them far longer to come into maturity, and they lasted many times longer than the trees in the commercial forest of conifers. They were well adapted to the soil, unlike many of the conifer forests that had been planted in unlikely places. He began to wonder if, for the health of the trees and the forest, it wasn’t better to manage as nature did, rather than to adopt the practices of forestry management—even so-called selective cutting and thinning and harvesting. Although he does not reference Thoreau, 150 years ago Thoreau came to the same conclusion, on reading an English book about planting walnut trees.
    Searching for an explanation about why this beech forest that seemed to violate all the principles of forestry management was able to maintain itself better than the managed one, he read reports by scientists. What most intrigued him was a paper published in 1997 by Susan Simard as lead author. Simard and her group observed that in the forest soil, fungi attach to tree roots and that, when trees grow close to each other, the roots and fungi of different trees intertwine, even among different species, and transmit carbon and other chemicals (glucose, for example) from one tree to another. In effect, the trees were feeding one another. Afterwards, Wollheben began to read of other experiments in which trees seemed to “help” each other, for example by sending out scents signaling the presence of a pest, that would cause other trees in the forest to erect chemical defenses against the pest. It was not a big step for him to conclude that the trees in a forest constituted a kind of symbiotic community, even though they were also in competition with one another for sunlight and water.
    One of the corollaries of this research, he concluded, was that trees closer to each other can help each other more—they are better off that way. Not only are their entwined roots better able to reach each other and exchange food, but the stronger trees often “feed” the weaker ones because it is beneficial to keep them all alive so they can “help” each other. When I walk out in the un-managed spruce forest behind my own house, I hear tree branches and sometimes the trunks, high up, rubbing against each other when there is a strong wind. I used to think that was unfortunate, that the trees were too close together. Now, after reading Wollheben, I realize that they are propping each other up against the possibility of breaking off or toppling over completely.
    In early October, 2014, a snowstorm with high winds occurred where I live on East Penobscot Bay. It toppled many trees, also snapping off branches. The earth was wet from recent rains, making it easier for the top-heavy trees to become uprooted if they had no nearby tree to prop them up. I noticed there were more snapped and toppled trees at the edges of clearings. Also, four apple trees in an old, planted orchard had been uprooted completely. I was able to save two of them with the help of a neighbor, and get them back upright after pruning them back heavily; they are growing again, but the other two were beyond help.
    Consider, then, the advice given by professional foresters for planning an apple orchard: plant the trees at some distance from one another so they avoid their branches touching. For a full-sized tree, that should be forty feet apart in all directions; but such a tree will not be able to extend its roots to entwine with its neighbor, for the roots spread about as far under the ground as the branches do above. Those trees will also be more susceptible to damage from wind and insect pests. Of course, for easier harvest they are planted at that distance; but it would not be that much more difficult to harvest apple trees planted closer together. The apples might be more numerous, but they would be smaller, and many would not fully ripen unless the branches were pruned so that in a heavy wind they would not prop each other up.
    In nineteenth-century New England, when a house was built, a small home orchard usually was planted out behind the house, the tree trunks about fifteen feet from each other. You can find these commonly with the older houses still standing, and even when the houses are gone and only the cellar holes remain, and the surrounding area has grown up into forest, a home apple orchard is likely to found within seventy-five feet of the cellar hole. The full-sized trees that grew up were able to live long as their roots and branches entwined, and the apples they produced--for cider, baking, and fresh eating--were easily enough harvested, by climbing the trees or using pole harvesters for the best specimens, while the cider apples were gotten off the trees by shaking the branches. Such an orchard stands in back of my own house, and these trees were not damaged in the 2014 snowstorm the way those planted in a field nearby, according to proper orchard practice, were damaged.
    In short, the trees in a natural forest, according to Wollheben, comprise a community, a kind of mutual aid society while at the same time they are competing with each other. By means of mutual aid they are able to sustain the forest far better, and for far longer, than a forest planted or managed according to the principles of contemporary good forestry practice. The same principle might be applied to the management of music cultures. Indeed, I have embraced it in earlier blog posts here: feed the cultural soil, do not target the individual plant. In other words, encourage the music culture, not individual musical genres. If the cultural soil is nurtured, the musical genres will develop and thrive. An endangered music will not thrive if the cultural soil is not working in its favor, no matter how much it is aided.
   

Ecomusicologies 2014 and the Sounds of Plants

     Scientists have known for many years that plants emit sounds, and also that they respond to sounds—for instance, they make noises when fluids move rapidly up and down their stems. Plants also move towards or away from sounds as they also do when stimulated by light. From time to time, claims have appeared that plants grow better when spoken to encouragingly. The Daily Mail reported in 2009 the Royal Horticultural Society's conclusion that “talking to your plants can really help them grow faster.” Charles Darwin’s great granddaughter, Sarah, who took part in the Society's experiment, turned out to be the champion talker: reading from On the Origin of Species caused her plant to grow nearly two inches taller than the control. Elementary school science projects include experiments “to find out whether plants respond to human speech,” asking students to think about how plants communicate, what types of messages they send one another, and how vibrations affect plants.
    As an organic gardener, I knew that legume roots were colonized by nitrogen-fixing bacteria, but it didn’t occur to me to ask how the bacteria in the soil found the rootlets to grab on to. If I’d thought about it, probably I’d have said these were random encounters, or that perhaps the rootlets emitted some kind of chemical that was attractive to the bacteria. It would never have occurred to me to think that bacteria might have been responding to vibrations in the soil made by disturbances when the rootlets expanded and grew. But after listening to Monica Gagliano at the conference, and then reading many of her articles published in the scientific literature, I know that this is very much a possibility. Gagliano is an Italian scientist who worked in the laboratory of Stefano Mancuso, one of the most important contemporary researchers in the field of plant intelligence. Currently she's a postdoctoral research fellow at the Centre for Evolutionary Biology at the University of Western Australia.
    Gagliano claims that plants not only communicate with soil bacteria and other creatures, but that they communicate with each other, by means of vibrations which she is willing to call sound. “Vibrations are sound,” she replied when I asked her if she made any distinction between them. For a scientific realist sound is a feature of the external world and consists of waves inside a medium that are set in motion by vibrations. Plants, obviously, vibrate; their cells, for example, vibrate at the microscopic level continuously, just as human cells do. Perhaps the problem humans have in accepting plant communication via sound is that we commonly think of communication proceeding from vocal cords to ears, and of course plants have neither. But it doesn’t take long to realize that sound communication doesn’t need vocal cords—just think of musical instruments, or animals signaling by sounding parts of their bodies—and that sound vibrations can be felt in various parts of the body, not just the ears—think of the deep bass of an organ, for example. Assuming that communication is the transfer of information, then for it to take place there must be a transmitter, a receiver, and the information itself. On those grounds, plants qualify. Evolutionary biologists believe, further, that living creatures must have evolved through natural selection so that communication is a specific adaptation to their environment, not merely a by-product of some other activity.
    Gagliano reports that plants not only emit sounds but also detect them and modify their behavior accordingly. ”Preliminary investigations of both emission and detection of sound by plants indicate that plants have the ability to detect acoustic vibrations and exhibit frequency-selective sensitivity (i.e., plants respond to the same range of frequencies that they emit themselves) that, in turn, generates behavioral modifications. Hence, the relevant question is not about whether plants have evolved to detect and respond to sound waves or vibrations in their environment, but how and why they do it (italics in original).1/ These are all good questions, yet it seems to me that numerous additional experiments are needed before one can be reasonably certain that sound communication is normal among plants. Scientists may more confidently proceed to the “how” and “why” after more instances of the “what” are confirmed. Incidentally, I’m making the distinction here between sound communication between plants, versus that between plants and non-plants (e.g., bacteria, insects); I believe we have a good deal more evidence for the latter, and much less for the former.
    For readers who’d like an overview of plant communication within the larger field of plant intelligence, I recommend a New Yorker essay by Michael Pollan which appeared less than a year ago. (Thanks to Tyler Kinnear who called that essay to my attention.) Gagliano’s research is mentioned, but the essay focuses on the work of her mentor, Stefano Mancuso, and also gives a good deal of space to the skeptics who wonder whether it’s a stretch to call plants intelligent or communicative. Of course,  skeptics also cast doubt on animal intelligence and communication, claiming that the human varieties are different in kind as well as degree. Still, it seems to me that considering sound communication among animals, and even among plants, offers perspective on sound communication among humans, its evolution and functions, which must be helpful in considering sound, music, and sustainability over the long term for all living creatures.

1/ Monica Gagliano, "Green Symphonies: a call for studies of acoustic communication in plants." Behavioral Ecology doi:10.1093/beheco/ars206, 25 November 2012, pp. 789-796.