--- but it's not quite what you might think.
Scientists have been dealing with the problem of natural tree falls (and the
sound they make--or don't make) for quite some time and have drawn some rather surprising conclusions.
If a tree falls and there is a person around the sound is easily recognized.
If a tree falls in the forest and there is nobody nearby, the sound that it makes is very different and often not recognized as the sound of a tree falling.
Either way, there is a sound.
Even though plants do not show any changes to the naked (or lensed)
eye, when a human is in their presence systemic biological changes have been discovered that have grave effects on plant life when a person is within 300 meters. This effect is called "human stress syndrome".
Apparently, when a tree is about to fall, if it senses a human nearby the biological stresses of human presence cause the cell walls in the plant to become brittle and it is the cell brittleness responsible for the familiar
sound we know as that of a tree fall. The cell brittleness also has significant effects to the quality of the lumber, making it much more suitable for use in construction (see below).
Through the miracle of recording tape, we are able to provide a sound recording of an actual tree falling without human presence.