The idea that forest trees can “talk” to each other, share resources with their seedlings and even protect them through a connective underground network of fine fungal filaments tickles the imagination.
The concept is so intriguing that it has caught on in popular media even appearing on the popular Apple TV show Ted Lasso and has been dubbed the “wood-wide web,” but the science behind the ideas is unproven, warns University of Alberta expert Justine Karst .
In a peer-reviewed paper published in Nature Ecology & Evolution, which also shares their personal perspective, Karst and two colleagues challenge three popular claims about the ability of underground fungi known as common mycorrhizae networks, or CMNs, to connect the roots of multiple plants underground. Fungi are living organisms such as molds, yeasts and fungi.
Karst, associate professor at Charles University’s Faculty of Agriculture, Environment says “It’s great that the CMN research has sparked interest in forest mushrooms, but it’s important for the public to understand that many popular ideas are ahead of science”.
While CMNs have been scientifically proven to exist, there is no strong evidence that they offer benefits to trees and their seedlings, the researchers suggest. To evaluate the popular claims, Karst and co-authors Melanie Jones of the University of British Columbia Okanagan and Jason Hoeksema of the University of Mississippi reviewed evidence from existing field studies.
They found that one of the claims that CMNs are widespread in forests is not supported by sufficient scientific evidence. Not enough is known about the structure of the CMN and its function in the field, “with too few mapped forests”. A second claim that resources such as nutrients are transferred from mature trees to seedlings via CMN and that they increase survival and growth has also been found to be questionable.
A review of 26 studies, including one in which Karst is a co-author, found that while resources can be transported underground by trees, CMNs do not necessarily induce this flow, and seedlings typically do not benefit from CMN access. Overall, their review revealed roughly equal evidence that attachment to CMN would enhance or limit seedlings, with neutral effects most commonly reported.
A third claim that mature trees preferentially transmit sources or “warning signals” of insect damage to young trees via CMN is not supported by a single peer-reviewed published field study, Karst and her co-authors note. The researchers say that exaggerated information can shape and distort the public narrative about CMN, which in turn could affect how forests are managed.
Misrepresentation of the science of CMN in forests is a problem because good science is critical to decisions about how forests are managed. It is premature to base forest practices and policies on CMN per se, without further evidence. And failure to identify misinformation can erode public trust.
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