The woman who uncovered the secrets of the ‘Wood-Wide Web’
In August 1997, a smart sub-editor on the journal Nature coined the phrase “the wood-wide web” to describe the astounding subterranean fungal networks uncovered by a young researcher in Canada’s conifer forests. It was a catchy headline, and the image it conjured up has turned out to be transformative in the popular understanding of ecology.
Under the staid title of “Net transfer of carbon between tree species with shared ectomycorrhizal fungi”, Suzanne Simard’s paper blew apart two centuries of conventional wisdom about how trees lived together. Against the bleak zero-sum model of commercial forestry, in which every tree is forever trying to shade out, starve, or otherwise discommode its neighbours, she proved that woodland trees are linked by underground fungal threads, through which nutrients, water and information are equitably shared. The forest is a co-operative.
Simard grew up in a logging family in the wilds of Canada, eventually becoming a Professor of Forest Ecology at the University of British Columbia. Mother Tree is a memoir of this improbable journey, as well as an account of the science behind her revelations. The two modes aren’t an obvious fit, but it’s invigorating, the way they feed off each other.
An early job as a researcher for a logging company had her checking the fortunes of spruce seedlings in a huge area of clear-cut. She found that, in line with the stare-approved policy of “Free to grow”, all supposedly competing vegetation had been razed to the ground or sprayed out. She was heartbroken by the result: biodiversity decimated, all big shelter trees felled, the planted seedlings wretched and diseased. Her early experiments showed that blacklisted “weed” trees like alder actually draw up water and fix nitrogen for use by other trees. Soon she began to suspect that these, and other vital resources – sugars and mineral nutrients – are not just drifting about in the soil, but actively being shared through a network of underground fungi called mycorrhizas.
Mycorrhizas are well-known symbiotic arrangements. Most orchids, for instance, have intricate entanglements between their root-tips and various fungal “roots” (hyphae). The orchid’s green leaves produce the sugars which the fungus cannot manufacture, and in return the fungus donates nutrients by breaking down organic matter in the soil. Mycorrhizas were known to involve tree roots too, but no scientist had dared suggest that they were involved in a forest-wide communication network. Over the next decades, via a series of increasingly elegant and arduous field experiments, that is what Simard set out to prove.
I can’t think I’ve read a more vivid account of the realities of fieldwork, of how the forensic business of research is embedded in the messy contingencies of real life. Simard’s science is as rich with social connectivity as the forest she is investigating. She enlists her backwoods family as research assistants. She has one eye always open for grizzly bears, and for the more approachable beings whose flavoursome local names (tow-headed babies, hoary marmot) leavens the hard data.
Her prose is sometimes breathless, and her frequent use of human analogies and metaphors won’t go down well in some quarters. But I found it a glorious assertion that science is a human business, framed by the researchers’ world views and emotions. Simard agonises over the necessity to kill saplings to provide a control in one of her experiments – and then finds she has inhaled the herbicide through a faulty mask. And all the while she has to cope with the humiliation of a largely male forestry establishment, trashing her findings.
In the 1990s, her argument shifted to a different level. From what she had seen of mycorrhizas in the soil and the ways trees grow together in the wild, Simard had an audacious hunch. Groups of firs, say, aren’t just sharing sugars and nutrients amongst themselves. The fungal networks are distributing them to other species, too.
In the 1980s, the British biologist Sir David Read had used radioactive carbon to show that there was a flow of nutrients between pine seedlings inside a closed tanks. The flow could be tracked with a geiger counter. Simard now set up a dangerous series of experiments using a similar process in the wild. She put domes filled with radioactive carbon isotopes over fir and birch saplings (and got irradiated herself), and isolated the root systems of others with cylindrical shields. After a few days she took samples from the saplings and analysed them. The results were unequivocal: carbon is being shunted by mycorrhizas from birch to fir, and from fir to birch. It looks as if there is a seasonal cycle, with the birch being the donor in summer, when its leaves are manufacturing sugars, and the evergreen fir the donor in winter. Simard seems to have demonstrated that anathema of hard-line biologists: altruism between species.
Simard’s personal life was evolving too. She left the dogmas of the forest service and took up an academic post, married a colleague and had two daughters. Her account of a long struggle with breast cancer is filled with the same wistful regret as her stories of felled trees. And it was at this point, painfully aware that her daughters may lose her, that she began to organise her findings around the concept of ‘The Mother Trees’. She’d found evidence that the oldest trees in the forest are nodes in the underground network. They have the greatest density of mycorrhiza and seem to preferentially “send” nutrients to their own seedlings. But is this what is really happening? When she was new to the underland and in thrall to toadstools, Simard might have talked of ‘The Mother Fungus’ instead. Mycorrhizas have agency too, and they may be the ones controlling the flows of energy, maintaining the health of all their food sources for their own good.
But what she has really shown in this warm, and profoundly important, book is that forest vegetation is non-hierarchical. It is a self-organising network, full of feedback loops and homeostasis, with no one individual in control, like a swarm or a starling murmuration.
This is hard for us to grasp. Our very grammar is founded on the idea of subject and object. But in her final chapter Simard has a stunning vision of connectivity – grizzly bears bringing salmon to eat under the mother trees, leaving “fine corsets of bone folded like butterfly wings… the essence of the fish slowly absorbed by the roots, transmitted into the wood of the trees, passed to the next life.” “Tree bones” she exclaims, and who can blame her here for a metaphor from which, as a species, we could well learn.
Finding the Mother Tree is published in paperback at ￡10.99. To order your copy call or visit the Telegraph Bookshop
