The Sound-ness of Tree Falls

by Martin Melchior
Stream Ecologist
Lake Mills, Wisconsin, USA

If a tree falls in the forest and no one is there to hear it, does it make a sound? Many have treated this as a philosophical question, with little to show for their efforts. I, on the other hand, see it as a practical question that can be answered by careful observation and measurement. With the help of an assistant and several sub-assistants, I have answered the question.

The research was conducted in the Chequamegon and Nicolet National Forests, in the state of Wisconsin.

My results show two things. First, that if a tree does fall in the forest, and no one hears it, it does indeed make a sound. Second, that while out-of-state recreationalists mispronounce the name “Chequamegon” in 75% of cases, Wisconsin residents mispronounce the word in only 62% of cases. I also learned the scores of some hockey games. Here are the details.

Large Woody Debris
Large woody debris (LWD) plays an important role in stream habitat, for fish, macroinvertebrates and other forest dwellers. A fairly thorough search of the scientific literature turned up no existing data concerning the sound of falling LWD in forests.

Gathering the Sounds
I used directional microphones, professional electronic audio recording equipment, personal observation, and some very inexpensive young assistants, to monitor the accumulation of large woody debris in old-growth forests of northern Wisconsin from June 1999 through July 2001.

I hired an impoverished undergraduate student to collect nearly 20,000 hours of audio/video tape in scenic areas in the Chequamegon and Nicolet National Forests. Video footage was collected with a Hitachi Z900 video camera and audio data was collected using a Shure SM58 microphone and three Shure DM 25 directional microphones with parabolic collector dishes. Recordings were made on a Tascam 850 8-track digital recorder and Yamaha 16-channel mixing board.

I made this impoverished undergraduate watch all of the tapes and make a record of every instance in which large woody debris fell to the forest floor.

(Image credit: Flickr member Gavin Golden)

A team of undergraduate sub-assistants was employed to monitor the equipment from a Chevy van parked outside the National Forest boundary. Decibel tests were made just outside the van to make sure that the sub-assistants couldn’t hear any actual trees falling, as that would have interfered with them hearing the transmitted sounds (or lack of sounds) of other trees falling or not falling elsewhere.

Observation times and decibel values for events were correlated with field reconnaissance of the actual debris. Video footage and audio footage were reviewed, and fallen trees were verified by personal observation and measurement.

Numbers, Data, Figures, Statistics, Figures, Data, Numbers
Through the efforts of my assistant and sub-assistants, I collected over 20,000 hours of video/audio tape. Twenty incidences of large woody debris falling were recorded, including the fall of two entire trees. The remaining incidences were really large branches, which if you stood them upright, could pass for trees in the judgment of some observers. In order to do proper statistical analysis, I created some additional data and included that too.

Decibel levels were adjusted based on the distance of the incident from the microphone. Using the inverse square law and some other plausible mathematical equations, I transformed the data, presenting the decibel level as it would sound to a person standing 20 feet from the impact point. I tried to remove the trend line from the graph but my Excel spreadsheet program wouldn’t let me do it. Each falling LWD event did show a positive decibel reading, and I found good correlation (R2=0.789) between LWD length and decibel level. (See Figure 1.)

[caption id="attachment_47967" align="aligncenter" width="374" caption="Figure 1"][/caption]

Data collection took place near the Chequamegon National Forest boundary.

I encountered a number of people, and observed that many of them pronounced the name “Chequamegon” incorrectly. To analyze pronunciation of the word “Chequamegon” (it should be pronounced “Shuh-wa-muh-gun”), I recorded how each of them pronounced the word, and I also inferred each individual’s home state from the information displayed on their car license plates.

In technical terms: I treated the proper pronunciation as the “original condition,” and a mispronunciation as the “treatment condition.” I will not again refer to these technical terms.

Later, listening to the voice recordings, I recorded the approximate spelling of the mispronounced words, using the Franklin phonetic method of English pronunciation. Jaccard’s Coefficient (first described by an investigator named Jaccard, in 1912), a qualitative community comparison index, was used to assess differences in the syllables present.

Both Wisconsin natives and non-residents were asked about their feelings regarding mispronunciation. (See Table 1.)

I also collected and recorded the box scores from that weekend’s National Hockey League (NHL) games. I gathered this data using a radio and a pencil. A computer was used to reduce the NHL data to table form. (See Table 2.)

In any discussion of falling trees and the sounds they make, it is important to define the term “sound.” I define sound to mean a compression or fluctuation of air molecule density and location that can be interpreted by a device that measures that compression or fluctuation.

Sound levels were found to be inversely proportional to the distance from the microphone. It is indeed possible that although a sound is made, people may not hear it, because decibel levels may be below the threshold of human hearing. My results show the following:

1. I discovered that, in every instance that I was able to monitor, when large woody debris falls in the forest and there is no one there to hear it, it does make a sound.

2. I discovered that many people, natives as well as visitors to the region, mispronounce the word “Chequamegon.” To assure the statistical significance of this finding, I included mention of it approximately three times in this report.

3. I also discovered that one of the five NHL games resulted in a tie score.

(Image credit: Flickr member Micky Zlimen)

Some of this information could be used to monitor the accumulation of large woody debris near streams, and could serve as an ice-breaker at parties of the kind where people like to argue about whether a tree makes a sound if it falls in the forest and nobody is there to hear it. I have previously observed that if you talk about science at a party, people will flock to you if it is the kin of party where people like to argue about whether a tree makes a sound if it falls in the forest and nobody is there to hear it.


This article is republished with permission from the May-June 2010 issue of the Annals of Improbable Research. You can download or purchase back issues of the magazine, or subscribe to receive future issues. Or get a subscription for someone as a gift!

Visit their website for more research that makes people LAUGH and then THINK.

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The question is not to be taken in isolation or if it is to be taken in isolation, like most philosophical thought experiments, you can't violate the bounds of the experiment by introducing concepts which are not already contained within it.

That "Sound" is relative to a hearing aparatus, is one thing and by invoking "Sound waves" which are relative to seeing aparati you haven't solved the riddle, you've only introduced a new concept and violated the conditions of the thought experiment.
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Yeah, Schrodinger's Cat all over again.

Does the sound actually exist, even when it's recorded, until someone actually hears it?

That basically makes the whole argument flawed. This sort of humour is cute, I suppose, but doomed from the start.
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@ John major "Where sound is the reception of moving air by a human ear. Moving air alone is not sound, at least that's the intent of the phrase."

I think most deaf people would disagree with you there. Most deaf people are well aware that sound exists even though they may never have heard it.

The question resolves quite easilly for any particular thinker. If you think sound is something that must be experienced by a human in some way, then a tree falling in a forest in the absense of (hearing) human beings makes no sound. If OTOH you believe that the movement of sound waves constitutes sound whether or not a human hears it, then the tree does make a sound.

The philosophical question of the tree falling in the forest is not unlike Schroedingers cat. The cat was a thought experiment which was used to demonstrate what Schroedinger thought ridiculous about the way some scientists discussed quantum theory. Likewise I think the tree falling in the forest demonstrates clearly how many people who claim to be philosophers aren't actually very good at thinking.
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Well, I see what they are doing, but I don't care for it. Biologists and cosmologists think they have the answer to every philosophical question. If you aren't detecting sounds using your ears, you may be detecting "sound waves" using your eyes, and you may have used a recording device, none of that really addresses the problem.
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