We can’t see wind, only the things it moves. Likewise, we can’t hear wind unless it’s flowing past something that makes it vibrate; this causes it to adopt various sonic guises depending on what it interacts with. Trees provide some of the most common and admired ways for wind to make itself heard. This sound has been termed psithurism (sith-err-iz-um).
The naturalist author and founding member of the RSPB, W.H. Hudson, suggests in Birds and Man (1901), that psithurism is salubrious. He describes the sound of wind in the trees as “very restorative” – a mysterious voice which the forest speaks to us, and that to lie or sit thus for an hour at a time listening to the wind is an experience worth going far to seek.
The sonic qualities of psithurism seem to smudge the border between music and noise. The American poet Henry Wadsworth Longfellow (1807-1882) described the sound in “A Day of Sunshine”:
“I hear the wind among the trees
Playing celestial symphonies;
I see the branches downward bent,
Like keys of some great instrument.
The type of leaf, the season and the species of tree all work together to create a unique sound, or as John Muir put it: “Winds are advertisements of what they touch”. He described how, in the wind, each tree expressed itself in its own way, “singing its own song, and making its own peculiar gestures”. Of all the tree species the sounds of the pine seems to have captured the imagination of naturalists more than any other. Muir suggests pines are the best interpreters of the winds. “They are mighty waving golden-rods, ever in tune, singing and writing wind music all their long century lives.” (A Wind Storm in the Forests of the Yuba, 1878).
Thoreau also had an affinity for the wind through the pines: “The white pines in the horizon, either single trees or whole wood, are particularly interesting. The wind is making passes over them, magnetizing and electrifying them…This is the brightening and awakening of the pines…As if in this wind-storm of March a certain electricity was passing from heaven to earth through the pines and calling them to life”. (Journal of Henry David Thoreau 1855-1861).
Eastern thinkers also noted the distinctiveness of pines. Shunryu Suzuki (1904-1971), a Zen monk and teacher, describes with typical equity, psithurism and the mind:
“When we hear the sound of the pine trees on a windy day, perhaps the wind is just blowing, and the pine tree is just standing in the wind. That is all that they are doing. But the people who listen to the wind in the tree will write a poem, or will feel something unusual. That is, I think, the way everything is.”
Finally, perhaps the earliest and loveliest writing on the subject of arboricultural acoustics is by Liu Chi (1311-1375), an important scholar under the Yuan and the Ming Dynasties, who wrote that:
“Among plants and trees, those with large leaves have a muffled sound; those with dry leaves have a sorrowful sound; those with frail leaves have a weak and unmelodic sound. For this reason, nothing is better suited to wind than the pine.”
“Now, the pine as a species has a stiff trunk and curled branches, its leaves are thin, and its twigs are long. It is gnarled yet noble, unconstrained and overspreading, entangled and intricate. So when wind passes through it, it is neither obstructed nor agitated. Wind flows through smoothly with a natural sound. Listening to it can relieve anxiety and humiliation, wash away confusion and impurity, expand the spirit and lighten the heart, make one feel peaceful and contemplative, cause one to wander free and easy through the skies and travel along with the force of Creation. It is well suited to gentlemen who seek pleasure in mountains and forests, delighting in them and unable to abandon them….Gazing at the pines soothed my eyes; listening to the pines soothed my ears. I escaped from my duties and with this leisure time wandered free and easy here and there without any worldly concerns to perplex the mind. I can feel happy here and pass the entire day this way.
Working as tree consultants undertaking expert tree surveys, we use Visual Tree Assessment techniques to identify signs and symptoms of ill health and structural failure across a wide range of tree species. We occasionally use ‘micro-drills’ or ‘Sonic Tomographs’ to detect and quantify decay in trees. Yet there also times when simply listening to the sound of wind through the tree – the swaying, bending and creaking and the flow of air through the foliage – can highlight issues about tree health that our eyes did not immediately detect.