Scientific Tangle: The Wood-Wide Web

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Issue 1, Volume 114

By Shaon Anwar 

In the past decade, the idea of trees “whispering” behind our backs has sparked popular interest and controversy. The Netflix documentary Fantastic Fungi (2019) by Louie Schwartzberg takes us on an immersive journey through the enchanted fungi kingdom, “from mushrooms that clear oil spills to underground fungal networks that help trees communicate.” Using intricate time-lapse photography, the film depicts the sprawling connection between fungi filaments and the tree roots that swap carbon and nutrients. The extraordinary claim that trees cooperate and transfer resources via fungal lattices has seeped into academic literature and been embraced by popular culture. However, recent studies show that the assertion of mycorrhizal networks facilitating tree communication rests on precarious data, leading to misinterpretations. The narrative serves as a cautionary tale for both scientists and journalists.

  The “wood-wide web,” a phrase coined in 1997 in Nature, describes a map of tangled fungi (living on plant roots) and trees working hand in hand, replacing the Darwinian idea of fiercely competing groups of organisms. The notion exceeds the basic mutualistic relationship between mycorrhizal fungi and trees, in which the fungi take carbon-rich sugar from the tree, and in turn, the tree receives phosphorus and nitrogen. The wood-wide web refers to a common mycorrhizal network (CMN), a structure linking the roots of two neighboring trees through a fungal filament that stretches out across forest soil, which facilitates the transfer of nutrients. In her research paper, “Net transfer of carbon between ectomycorrhizal tree species in the field,” Dr. Suzanne Simard, an ecologist at the University of British Columbia, compares the idea of cooperation between trees in forests to “mother” trees caring for younger seedlings by sending carbon underground through CMNs. Simard contends that these older trees support weaker seedlings by providing additional resources; birch trees, for example, support fir seedlings by providing nutrients and sugar. Simard explains that the network serves as a lifeline; without much access to sunlight, seedlings rely on sugar pumped by parent trees. Not only do CMNs provide food, but trees can use them to send one another warnings about impending insect attacks. 

Despite these studies, there is also contradictory evidence that uproots the idea of communal trees using the mycorrhizal conduit to trade and communicate. A 2023 study published in Nature Ecology & Evolution by Dr. Melanie Jones, Dr. Justine Karst, and Dr. Jason Hoeksema raises questions about how and to what extent trees interact through CMNs. The study examined 28 field studies and found little to no evidence that backed the claim that CMNs are widespread and help seedlings thrive. The researchers described the difficulties of studying a mycorrhizal network; delicate fungal treads break easily and can grow individually, making it impossible to discern which harvested filaments are connecting two trees, even through genetic sampling. Such fungal DNA sequencing was only achieved in five studies on a limited variety of fungi and tree species. All of Simard’s studies of the wood-wide web were done in a forest in western Canada, populated by mostly Douglass-fir trees. This limitation underscores the extent and lifespan of CMNs and the application of the research. Even in a well-controlled 2008 study, published by plant ecophysiologist Dr. Jeffery M. Warren, mesh was used to separate roots, which allowed fungi to link Ponderosa pine seedlings to older pines and for dyes to show nutrient transfer. The results indicated there was no strong evidence for improved seedling performance. In only 18 percent of analyzed studies, it was noted that the beneficial effects of CMNs on seedlings outweighed the negative effects of root connections. This finding was not enough to lead to a general conclusion regarding reciprocity between the mature tree and the seedling via CMNs. Alternative explanations exist for this transfer of resources without the involvement of CMNs. For example, it is possible that nutrients travel from the roots of neighboring trees or through porous soil. Moreover, the widely reported idea that trees share underground warning systems was predicated on a single study conducted in a greenhouse. Karst concludes that the concept of signal exchanges between trees has not been scientifically supported, and more research is needed to better understand these mycorrhizal connections in forests. Yet, even without much experimental certainty to back it up, the story of communicating trees captured popular attention.

Jones compares the narrative about forest and fungi taking a wrong turn to a game of telephone. Original research has been distorted by omitting alternative hypotheses and through the addition of inaccurate and exaggerated statements. Jones also points to confirmation bias, citing positive effects that may obscure and influence our understanding of the structure and function of CMNs in forests. As scientists fell into the trap of potentially sensational findings, popular culture followed by amplifying romanticized views of forests as benevolent and cooperative. The narrative of the wood-wide web and anthropomorphizing trees reflects what people want to see. “I’m just in love with what they represent,” Schwartzberg reflected. “This idea of a network that shares… is sort of the model that we need to live our lives on.”