Submitted by Paul Hetzler, ISA Certified Arborist

The term psithurism (sith-er-izm) doesn’t exactly roll off the tongue, but it’s not meant to. The word, from the Greek psithuros (whisper), indicates the melody that rolls off pine needles in a gentle wind. It also means the sound of “proper” leaves shaking in the treetops. Obviously, we need another word, because these two things – whispering pines and rustling leaves – may both soothe us, but they sound quite different.

In our little home in the Gatineau hills, we’re lucky that the house is shielded on the west by an unusually large and spreading yellow birch. One breezy morning when the windows were open, my wife remarked how different the birch sounded in the wind compared to the sugar maple, which is on the other side of the house. When I paid attention, it was clear she was right: the birch had a softer tone than the maple. I laughed that a city girl should make an observation that a longtime arborist had not.

In my defense, the matter of arboricultural acoustics had not escaped me entirely. The sound of a breeze passing through a poplar grove is unique. Everyone who’s had the pleasure of hearing this will probably have their own depiction, but I liken it to very distant applause, or the imagined noise of a thousand dragonflies passing overhead as their gossamer wings touch one another.

My curiosity piqued, I then searched in vain for some kind of catalog which described the sound of wind in trees, listed by species. Evidently, no one has yet been sufficiently bored or compulsive (or both) to undertake such a project.

Some other interesting things came up, however. I stumbled upon a beautiful passage written by a 12th century Chinese scholar named Liu Chi. Of course I would’ve had no idea what it said, but luckily it was a translation. Here is an excerpt from Liu Chi’s love letter to pine psithurism:

“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. 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.”

Wow – if that doesn’t make you want to run right out and sit in a pine grove, nothing will.

Not only do trees wash away our confusion as they whisper to us, they also quiet our voices. And the din from our motor vehicles. Many people notice how much farther sound seems to travel in the fall after all the leaves are off. Because vegetation helps dampen sound, urban planners and engineers try to incorporate noise barriers in the form of trees in order to make their cities more livable.

A buffer which is between 15 and 30 metres wide and densely planted in trees will reduce noise by as much as 8 decibels. When the same size tree buffer is atop a four-metre tall berm, noise falls off between 10 and 15 decibels. This may not seem like much, but it can make the difference between ambient noise with long-term harmful consequences and noise that is safe to live with.

Species and size make a difference as well. Deciduous trees are most effective, but conifer species are generally used so that the benefit is year-round. Also, younger trees are better at dampening sound than mature ones. Barrier effectiveness increases until trees are about 12 metres tall, after which their benefit slowly declines. For this reason, understory species as well as shrub borders along barrier edges are important. Hopefully the wind in these buffer-strip pines can still be discerned on occasion.

I urge everyone to get out as soon as possible to “relieve anxiety and humiliation, wash away confusion and impurity, expand the spirit and lighten the heart” by listening to breeze-tossed pines. Also, please help think of a companion word to psithurism that we can apply strictly to deciduous trees. Rustling just isn’t the same as whispering.

Paul Hetzler is an ISA-Certified Arborist and a member of the Society of American Foresters, the Canadian Institute of Forestry, ISA-Ontario, and NYS Arborists. He needs to listen more to his wife, as well as pine trees.