Trees are an integral part of our natural world, providing oxygen, shade, and beauty. But could these quiet giants actually be making noise that we just can’t hear? Let’s take a closer look at whether trees might yell or make other vocalizations.
How do trees communicate?
Trees have various methods of communicating with each other and other organisms. These include:
- Chemical signaling – Trees release chemicals called terpenes to warn nearby trees of insect attacks or other threats.
- Mycorrhizal networks – Fungi living among tree roots form interconnected networks between trees through which trees can share nutrients and information.
- Leaf and branch movement – Trees can indicate wind direction and strength to other trees through natural movement of their leaves and branches.
However, trees lack vocal cords and other anatomical features required for yelling or making sounds as animals do. But some scientists believe trees can make sounds at frequencies below the range of human hearing.
Evidence that trees make sounds
A few key research findings suggest trees may vocalize in ways imperceptible to us:
- A study in 2019 found timber trees make clicking sounds at a frequency of 220 Hz, likely caused by sap moving inside xylem cells.
- Research in the 1960s showed oak and maple seedlings emitted clicks and cracks at ultrasonic frequencies when undergoing drought stress.
- Experiments have picked up ultrasonic acoustic emissions from trees during freeze-thaw cycles in winter and spring.
So while trees don’t yell in a sense we can hear, some scientists think they vocalize using sounds or vibrations beyond our auditory range.
Possible purposes of tree sounds
If trees really do emit noises inaudible to us, these sounds could help trees:
- Sense danger – Sounds could alert nearby trees to threats like drought, pests, or extreme weather.
- Measure health – Changing sound patterns may indicate reduced water flow or stunted growth.
- Communicate – Trees may relay information important for survival using acoustic signals.
Think of these hypothesized tree sounds like a forest murmur: a constant low-level chatter we’re unaware of.
Can technology detect tree sounds?
To better understand if and how trees vocalize, researchers use specialized recording devices and laser-based tools to analyze tree movements, vibrations, and noises.
Acoustic monitoring
Sensitive microphones and accelerometers can pick up ultrasonic sounds and vibrations from trees that humans can’t hear. Researchers place these acoustic recorders against tree trunks, branches, and roots to monitor noise patterns.
Laser vibrometry
Lasers directed at a tree surface precisely measure tiny vibrations in wood and other tissue, allowing detection of ultrasonic noises. This non-contact method avoids disrupting the tree’s environment.
Sap flow sensors
These sensors placed inside trees measure internal sap flow, which may cause subtle tree vibrations. Drops or surges in sap flow could trigger corresponding sound changes.
Seismic sensors
Buried underground, seismic sensors record minute earth vibrations from trees that could correspond to underground root chatter or movement.
Advanced tools like these are beginning to uncover the acoustic energy inside trees that goes unnoticed by the human ear.
Recent research into tree sounds
Cutting-edge studies are finding new evidence that trees produce a range of sounds and vibrations:
Ultrasonic noises from drought stress
A 2022 study using acoustic emissions testing found poplar seedlings generated ultrasonic clicks and snaps when subjected to drought conditions. These stress sounds may help share information between trees about water availability.
Noises during freeze-thaw cycles
Research in 2022 placed acoustic sensors on tree trunks and found evidence of ultrasonic noises as the trees underwent freeze-thaw transitions in cold temperatures. This suggests internal damage from ice formation and melting may produce noise.
Underground root chatter
A 2021 study buried geophones near tree roots and recorded seismic events indicating complex underground signaling between trees and fungi associated with their roots. This root “chatter” may relay important messages.
Sap flow and sound correlation
Analyzing tree sap flow and sounds in 2022, researchers found increased sap flow corresponded with more ultrasonic noise events. This hints that internal sap circulation could create subtle tree murmurs.
As monitoring methods improve, scientists are gathering more proof that trees produce a wide array of noises, vibrations, and ultrasonic waves.
The future of tree acoustics research
This emerging field of study has great potential to continue revealing the acoustic abilities of trees:
- Developing new sensors – Better ultrasonic microphones and vibration detectors can capture more tree sounds.
- Large-scale field studies – Acoustically monitoring many trees in forests long-term can uncover patterns.
- Lab experiments – Simulating stresses on seedlings and saplings could clarify reasons for ultrasonic noises.
- Mathematical modeling – Computer models to analyze audio data may find hidden patterns and meaning.
Through an array of innovative technologies and research approaches, our understanding of tree acoustics is poised to grow dramatically in the coming decades.
Uses for tree acoustic monitoring
If studies conclusively show trees emit meaningful noises, we could put this knowledge to practical use:
Forest health tracking
Acoustic sensors in trees may provide remote monitoring of forest drought stress, infestations, or disease outbreaks based on increases in unusual ultrasonic noise.
Tree structural assessment
Subtle changes in internal wood sounds could give early indications of structural issues like cracks, cavities, or decay.
Emergency tree risk alerts
Networked acoustic sensors could provide instant warning if dangerous ultrasonic noises suggest a tree is about to fall.
Environmental impact evaluation
Trees’ ultrasonic noise patterns may reveal if human activities like construction or roadwork are disturbing them.
Continuous acoustic monitoring could give us a new perspective on forest and tree health while we’re not physically present.
Conclusion
The prevailing scientific consensus remains that trees do not vocalize in an audible sense. However, a growing body of research proposes our wooden giants fill forests with an endless stream of secret chatter broadcast at sound frequencies beyond the reach of human ears. As monitoring technologies progress, our understanding of these ultrasonic tree murmurs will continue improving, opening up new possibilities for understanding and communicating with our arboreal neighbors in the plant kingdom. The key takeaways about tree acoustics include:
- Trees lack vocal cords but may make inaudible sounds
- Specialized tools can detect ultrasonic noises from trees
- These tree sounds may communicate threats like drought
- Research is still just beginning on the acoustic abilities of trees
- Deeper study of tree noises could aid forest health monitoring
While it’s unlikely we’ll ever hear overt yelling from trees, science continues to uncover the rich complexity of arboreal life. Our silent green giants may speak volumes in frequencies we cannot hear, but instrumentation and research will decipher more of this tree talk in the years ahead.