Forest ecologist Suzanne Simard's research says trees talk to each other. Others aren't so sure

A renowned forest ecologist from B.C. is defending her research on how trees communicate after a citation review claims there is insufficient evidence to support her work.

Suzanne Simard, a forest ecology professor from the University of British Columbia, gained international recognition for her research into forest communication networks. Her findings say trees in a forest are interconnected and communicate with each other through underground fungal networks — colloquially dubbed as the "wood wide web." 

She is a leading figure in this body of research, spearheading a long-term experiment called The Mother Tree project. 

Simard's work, which includes a New York Times bestselling memoir, describes how trees are connected to each other through fungi on their roots called mycorrhizae. Through mycorrhizal networks, Simard says, trees are able to exchange resources, sharing nutrients with younger saplings and releasing chemicals to warn each other of distress.

But authors of a citation review published in Nature Ecology and Evolution say this research might not be applicable to every forest. 

Review co-author Justine Karst, who studies mycorrhizal ecology of forests at the University of Alberta, says she is questioning the claim that mycorrhizal networks are widespread in forests. The article says only two forest types have been investigated — Douglas Fir forests in B.C. and pine forests in Japan.

"It would be really valuable to map more common mycorrhizal networks in different forest systems across the world," Karst said.

Karst and her co-authors' analysis also questions the study's claims that fungal connections benefit seedlings and trees can recognize their kin through mycorrhizal networks.

Simard told CBC the article misses a major point about the research, maintaining that studying interactions between trees is crucial for protecting forests.

"The article really focuses on a very narrow part [of the research]," said Simard. "That doesn't change the idea that forests are connected communicatively. And the fact that we need to look after these relationships, to tend to them and to care for them — that doesn't change either."

Karst said they are not disputing the importance of mycorrhizal fungi in forests, but question their influence of fungal connections in how trees function, saying there is also a possibility that nutrients can transmit through other means, such as soil. 

"It's possible that the carbon is just moving through the soil," Karst said. "The roots exude some liquid, there can be carbon in that liquid. It then moves through the soil and is picked up by another tree."

Simard says she has conducted work that has shown how trees transmit resources below ground through multiple pathways. 

"I think what [the reviewers] are critiquing is that we've claimed that this mycorrhizal network is the only one in operation, and that's not true," Simard said.

"All the papers acknowledge that all of those pathways exist together and it makes sense that trees would have multiple ways of interacting, sharing and even competing for resources." 

Calls for more research

Melanie Jones, a UBC Okanagan biology professor and co-author of the review, is calling for other types of forests to have their fungal connections mapped.

"Like in the Amazon, no one has mapped these fungal connections there," Jones said. "Our concern is really that we shouldn't automatically assume these happen everywhere." 

Simard says she welcomes calls for more research.

"[More research is] always needed, especially in ecosystems as complex as forests. We need to work together as teams to really solve these complex problems," said Simard.

She says critiques are expected in research communities.

"It's normal for science to do reviews all the time and go back and forth," she said. "That's a normal part of the scientific method."