The Secret Lives of Tree Roots

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TThe buzzing underground networks of tree roots in forests hold more secrets than we thought: Scientists have now learned that roots time their growth based on who their neighbors are, and the winners in these competitive hierarchies aren’t always who you might expect.

This finding could have implications for whether the mixed forests that conservationists are planting today can survive climate change.

Most of what we know about seasonal cycles of tree root growth comes from studying stands of single tree species. But in nature, forests are usually mixed. Qiwen Guo, a doctoral student at the Institute of Forest Ecology at the University of Natural Resources and Life Sciences Vienna, wanted to know how a tree’s neighbors influence the dark underworld of its root system.

Read more: »Never underestimate the intelligence of trees»

To find out, she studied trees in an Austrian experimental forest, where the trees are equipped with minirhizotrons, a non-destructive root imaging and analysis technology that offers a glimpse into the underground world via transparent tubes. The experimental forest contains four common European tree species in different mixtures: oak, hornbeam, linden and maple. His biggest question was: Do roots adjust their growth schedule based on the trees around them?

It turns out that’s the case. Guo found that in mixed forests, one species is dominant and determines the rate of root growth of the rest, even though that dominant species is not always the most productive tree in the group when grown in monoculture. “We found that mixing rewrites the underground calendar: trees change the timing of their root growth in mixtures, often matching their dominant neighbors rather than adhering to individual schedules,” she writes in a recent behind-the-scenes essay about the work, published in the journal. Functional ecology. She also found that root growth depended on specific combinations of species, not just diversity.

The forest came to life as the scientists worked, and local residents often had different ambitions than the researchers: “The curious animals stealing our sensors left us both amazed and amused,” she adds. But their patience was worth it: “Our biggest surprise was the magnitude of the time lag: in monocultures, maximum root growth followed full leaf expansion by two to three weeks, but in mixtures this gap extended to about five weeks!

Roots begin growing before new seasonal leaves grow on a tree’s branches, but when trees are surrounded by other species, the time interval between peak root growth and full leaf development is longer, she notes. Indeed, some trees wait to suck resources from the soil until there is less competition from other species with conflicting growth schedules. In summary, the results suggest that the dynamics of belowground competition may differ significantly from expectations based on monoculture performance.

To collect their data, Guo and his colleagues photographed tree roots frequently, generating nearly 7,000 images, and spent up to an hour per image tracing individual roots. It was tedious work: “In the mixtures, identifying which species each root belonged to was tricky,” she writes. They also measured soil temperature every two hours and, above ground, tracked leaf development with fisheye images.

The results inspired a series of additional questions for future research: does mixing influence total biomass, the ability to collect nutrients from the soil, the types of fungal colonies that inhabit the forest? “And above all,” she writes, “how will climate-induced seasonal temperature changes disrupt the thermal signals that have regulated these phenological patterns for millennia?

This goes far beyond academic issues, she says. Solving these mysteries is key to predicting how Earth’s forests and roots will behave in a changing world.

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Main image: Chokniti-Studio / Shutterstock

• Kristen French

  Published on November 7, 2025

  Kristen French is an associate editor at Nautilus. She has worked in science journalism since 2013, reporting and writing articles and news for publications such as Wired, Backchannel, The Verge, And New York Review. She holds a master’s degree in science journalism from Columbia University.