Trees Can Get Stressed and Scream

While a walk through a quiet forest might seem peaceful, recent science suggests it's filled with sounds we simply can't hear. Groundbreaking research has revealed that plants under duress emit high-frequency noises that are beyond the range of human hearing. In a controlled study, scientists found that tomato and tobacco plants produced a flurry of ultrasonic "clicks," similar in volume to human conversation, when they were deprived of water or had their stems cut. A healthy, hydrated plant remained almost silent, but a thirsty one could emit dozens of these distinct sounds per hour, creating an acoustic record of its stress.

This phenomenon isn't a scream (Review) in a biological sense, but rather a physical process known as cavitation. Think of a plant's vascular system, the xylem, as a series of tiny straws pulling water from the roots to the leaves. When a plant is dehydrated, the tension on these water columns increases dramatically. This stress can cause tiny air bubbles to form and then violently collapse, creating a small shockwave that generates the ultrasonic popping sound. It is the acoustic evidence of the plant's internal plumbing beginning to fail under pressure.

Although we can't hear these sounds, other organisms certainly can. Many insects and mammals, including moths and mice, are capable of hearing in this ultrasonic range. This raises the fascinating possibility that these sounds are part of a complex, hidden ecosystem of information, potentially signaling to animals that a plant is weak or vulnerable. The discovery also has practical applications for agriculture, where farmers might one day use sensitive microphones to "listen" to their fields and irrigate with precision long before a crop shows visible signs of thirst.