Researchers are listening to the subtle symphony of soil to learn about the health of a forest. They found a chorus of high and low-frequency sounds in the soil of restored woodlands, compared with a quieter, less diverse soundscape in damaged habitats.
Ecologists have a long history of tapping into sound waves to glean clues about wildlife and ecosystems. The potential benefits of acoustic surveys are huge: scientists can gather information on species and their abundance with minimal disturbance and over long stretches of time. But until now, the practice has been limited primarily to above-ground or underwater sounds.
at Flinders University in Australia wondered if there was anything scientists restoring forests could learn from the sound of soil. Despite its rather inert appearance, healthy soil is packed with life and movement, from munching earthworms to growing tree roots, all of which make sound.
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Robinson began with the soil outside where he lives, scooping earth into a bucket and sticking a sensitive microphone inside. 鈥淚 got a very, very faint sort of signal,鈥� says Robinson. 鈥淚 thought, oh, yeah, I could be onto something.鈥�
Next, Robinson scaled up the size of the subterranean investigation, plunging microphones into the soil of healthy and cleared forests in South Yorkshire, UK. He and his team collected nearly 200 sound samples, each 3 minutes long. Some samples were collected from woodlands that had been logged within the last decade, while the 鈥渉ealthy鈥� plots had been recovering for up to 50 years.
The team stuck microphones directly into the soil and scooped soil into a sound-proof chamber in the field to pick up more subtle noises. 鈥淲e hypothesised that the restored soils would likely contain an abundance of different organisms and therefore we would likely hear a more diverse soundscape,鈥� says Robinson.
As anticipated, the researchers found that restored soil had more and a greater diversity of biological sounds compared with damaged earth when measured in sound-proof chambers. 鈥淚t鈥檚 like a trickling water kind of sound. You can definitely hear it,鈥� says Robinson.
Their in-ground measurements, however, yielded no significant differences. Robinson suspects that is because it is difficult to block out surrounding sounds, which can drown out the faint noises of scuttling bugs and shifting soil particles.
The research is 鈥渧ery well designed and thought out鈥�, says at Hochschule Geisenheim University in Germany. 鈥淢y first reaction was, 鈥楩inally. Yes, we need more studies like this to get better at below-ground biodiversity monitoring.鈥欌��
Listening to soil won鈥檛 entirely replace other survey methods, says Robinson. But he hopes the work provides a leap forward in low-cost, minimally invasive ways to assess the health of a forest.
