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trees: Rendering Ecophysiological Processes Audible


In our research project trees, we are working on the acoustic recording, analysis and representation of ecophysiological and climatic processes and studying the acoustic and aesthetic requirements for making them perceptible. Measurements of acoustic emissions in plants must be analysed and understood in relation to other measurement data such as that relating to the microclimate, sap flow, changes in trunk radius and water potential in the plants’ organs – all measurement data that is not auditory per se. Therefore, in our research project trees, we deal with the sonification of ecophysiological data as well as analysing the actual acoustic emissions: How can processes that are beyond our normal perception be made directly perceptible, creating new experiences and opening a new sight on processes in nature? To what extent is our sense of hearing of use?


Plant physiologists have known that plants emit sounds for several decades now. Most of these sounds are of transpiratory/hydraulic origin and are therefore related to the circulation of water within the plant as part of the transpiration process. The frequency of the acoustic emissions is in the ultrasonic range, i.e. well above the audible range. By analyzing these acoustic emissions, we can find out more about plant physiology and the ecophysiological processes in plants: If the sap flow is interrupted inside a plant’s vessels (a phenomenon known as “cavitation”), for example in a severe drought, the plant emits ultrasonic pulses that are imperceptible to the human ear – in other words, the plant begins to “whisper” in the high-frequency range. This phenomenon per se has been known for several decades and shows how atmospheric conditions, diurnal rhythm patterns, light conditions and water reserves manifest themselves acoustically, as it were, in trees.


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