Bringing the Sound Back to the Forest

For Omar Tello, our star restorer with more than 30 years of experience, one of the most important things he noticed during the process of bringing his land back to life was the resurgence of animal sounds. Thanks to these sounds, he says he can now finally rest. It is through the sounds that he has been noticing the arrival of species that did not exist in his forest before, and which constitute means of information as well as connections with biodiversity.

Sounds are an inexhaustible source of information. They can be classified according to the source that emits them. There are the sounds produced by human beings and their creations (also called anthropophony); and also those of non-human origin (called biophony and geophony). Anthropophony includes sounds generated by the human body (voluntary and involuntary) and those emitted through objects created by humans (such as machines). Also, within the biophony are the sounds generated through living organisms such as animals, plants and bacteria. Finally, the geophony is the sounds emitted by non-biological elements such as water, wind, fire and earth. We call soundscape the combination of all anthropophonic, biophonic and / or geophonic sounds generated in a given space and time.

In recent years studies have been conducted on what the soundscape can tell us about the forest’s health. Just as doctors listen to the heart of a patient to know if they are healthy, we--the echoacoustics--listen to the forests to determine its condition. We have realized that if we translate sound into images –through spectrograms of combinations of frequencies (measure of the wave vibration speed), amplitudes (measure of the maximum variation of wave displacement) and time– we will see that in a healthy forest all species occupy a specific place and tonality within the acoustic space, like a musical orchestra in which each instrument has its own space, tonality and time. Thus, the sound of the forest is harmonically distributed along the acoustic spectrum, the result of thousands of years of joint evolution between the forest and its inhabitants. Evolution has allowed species to adapt physically, as in the complex vocal apparatus of the howler monkey, and to also adopt a behavior of "respect for the position of others." More than a competition for sound space, we could say that there is a mutually beneficial relationship to listening and being heard. It is through the sound space that the inhabitants of the forest communicate with each other and know what happens inside the forest and, in this way, they can continue to perpetuate their species.

However, this sound arrangement is fragile and can be altered by human intervention. For example, in a forest where the sound of machinery noises is present, we can observe empty spaces in the spectrogram. This might indicate the absence of the singing of animals that inhabited the forest before the arrival of the noise. We call this the "empty forest phenomenon." In these cases, there could also be an overlap between the voices of species, as a result of the introduction of invasive species, or anthropophonic sounds (such as motor noise), within the same frequency range. This causes species to sing differently in order to adapt to the "new environment", by increasing or decreasing the frequency over time, or stop communicating altogether. Listening to sounds can also help us determine the state of health not only of the ecosystem itself but of a particular population. For example, there is more variety in the song of birds that live in non-fragmented habitats because they are healthier, have the resources they need to live and therefore sing more, than in affected areas. In other words, in a healthy forest we will have more singers and more varied music.

As new technology develops, scientists turn to it to continue searching for efficient answers and methods to assess and monitor the biodiversity and health of an ecosystem. The importance of listening more and understanding what the soundscape has to say is becoming increasingly apparent in the academic world. Curiously, scientific data on the subject increasingly point to what has already been said from ancestral Kichwa indigenous knowledge: "a healthy forest is a forest that sings." The relationship with sound is of vital importance for many Amazonian indigenous communities in Ecuador; the song of the forest is considered the life that manifests itself, and without it its culture would die.

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