The claim that forest trees “talk” through underground fungi is questionable

The romantic notion that trees communicate and cooperate with each other has been popular ever since the publication of Suzanne Simard’s much-praised book Finding the Mother Tree.  Simard and many ecologists have described a network of underground fungi that connects the roots of different trees (and other plants) to create what’s called a common mycorrhizal network (CMN). However, some scientists, like Justine Karst, an associate professor in the University of Alberta’s Faculty of Agricultural, Life & Environmental Sciences believe these depictions misrepresent ecosystems. While CMNs have been scientifically proven to exist, there is no strong evidence that they offer benefits to trees and their seedlings. Since scientists have yet to prove this underground network actually helps trees communicate with each other, the claim is half true. 

“It’s great that CMN research has sparked interest in forest fungi, but it’s important for the public to understand that many popular ideas are ahead of the science,” says Karst.

In an article published in Nature Ecology & Evolution, Karst and two colleagues contest three popular claims about the capabilities of CMNs. They found that one of the claims, that CMNs are widespread in forests, isn’t supported by enough scientific evidence. Not enough is known about CMN structure and its function in the field, “with too few forests mapped.”

The second claim, that resources such as nutrients are transferred by adult trees to seedlings through CMNs and that they boost survival and growth, was also found to be questionable.

A review of 26 studies, including one in which Karst is a co-author, established that while resources can be transferred underground by trees, CMNs don’t necessarily bring about that flow, and seedlings typically don’t benefit from CMN access. Overall, their review revealed roughly equal evidence that connecting to a CMN would improve or hamper seedlings, with neutral effects most commonly reported.

The third claim, that adult trees preferentially send resources or “warning signals” of insect damage to young trees through CMNs, is not backed up by a single peer-reviewed, published field study, Karst and her co-authors note.

The researchers say overblown information can shape and distort the public narrative about CMNs, and that could, in turn, affect how forests are managed. 

“Distorting science on CMNs in forests is a problem because sound science is critical for making decisions on how forests are managed. It’s premature to base forest practices and policies on CMNs per se, without further evidence. And failing to identify misinformation can erode public trust in science.”