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Suzanne Simard (1960–)

Simard demonstrated that trees in a forest are connected through underground fungal networks — mycorrhizal networks — and that they use these networks to share resources. Her experiments, beginning in the 1990s, showed that carbon, water, and nutrients flow between trees through the fungal hyphae that connect their root systems, and that the flow is not random: large, established trees (“mother trees”) preferentially support their offspring and neighbours, particularly those under stress. The finding challenged the prevailing model of forest ecology, which treated trees as individual competitors for light, water, and soil nutrients. Simard’s work suggests that forests are cooperative systems as much as competitive ones — that the underground network functions as a kind of communal infrastructure through which resources and chemical signals are shared. The popular label “wood wide web” (coined by Nature in a 1997 news piece on Simard’s work) captured the public imagination; the scientific reception has been more nuanced.

Life

Born 1960 in British Columbia, Canada. Grew up in a logging family in the Monashee Mountains; the experience of watching forest regeneration after clear-cutting shaped her research interests. Undergraduate at the University of British Columbia (BSF in forest resource management, 1983). Worked for the British Columbia Ministry of Forests for over a decade, conducting field research on forest regeneration. PhD at Oregon State University (1997), with a dissertation on carbon transfer between trees through mycorrhizal networks. Professor of forest ecology at the University of British Columbia (2002–).

Simard’s career trajectory — from ministry forester to academic researcher — is relevant: her questions arose from practical forestry experience (why do planted seedlings fail in clear-cuts but thrive in mixed forests?) rather than from purely theoretical concerns. The practical origin gave her work a policy dimension from the start: if forests are cooperative networks rather than collections of individual competitors, then forestry practices (clear-cutting, monoculture plantations, removal of “weed” species) that destroy the network are counterproductive.

Finding the Mother Tree: Discovering the Wisdom of the Forest (2021) — her memoir — brought the research to a general audience and became a bestseller. The book is personal as well as scientific: it interweaves the forest-ecology research with Simard’s family history, her experience as a woman in a male-dominated field, and her cancer diagnosis.

Mycorrhizal networks and mother trees

Mycorrhizal networks. Most trees form symbiotic relationships with mycorrhizal fungi: the fungal hyphae colonise the tree’s root tips, extending the root system’s reach into the soil and providing the tree with water and mineral nutrients in exchange for sugars (photosynthetic carbon). Simard’s contribution was to show that these fungal networks connect multiple trees: the same fungal mycelium can link the roots of different trees, sometimes of different species, creating an underground network through which resources flow.

Carbon transfer between trees. Simard’s key experiments (published in Nature, 1997) used radioactive carbon isotopes to trace the movement of carbon between trees. She labelled one tree with ¹³C and an adjacent tree with ¹⁴C, and measured the movement of each isotope. Carbon moved in both directions — from birch to fir and from fir to birch — through the shared mycorrhizal network. The transfer was net: more carbon flowed from the tree in sunlight (with surplus photosynthate) to the tree in shade (with a deficit). The result demonstrated that trees share resources through the fungal network and that the sharing is directionally responsive to need.

Mother trees. Simard’s later work documented that large, established trees (“hub trees” or “mother trees”) are disproportionately connected in the mycorrhizal network — they have more fungal connections, to more neighbours, than smaller or younger trees. Mother trees preferentially support their own seedlings (kin recognition through the network has been demonstrated in some experiments) and increase resource transfer to neighbours under stress (drought, disease, defoliation). When a mother tree is dying, it transfers carbon and defence signals to its neighbours, apparently investing its remaining resources in the surrounding network.

Where Simard stops

The “wood wide web” framing — forests as cooperative networks of trees sharing resources through a fungal internet — has been criticised as anthropomorphic and oversimplified. Justine Karst, Jason Hoeksema, and others published a systematic review (2023) arguing that the evidence for ecologically significant resource transfer through mycorrhizal networks is weaker than the popular narrative suggests. The isotope-tracer experiments demonstrate that carbon moves between trees through the network, but the quantity transferred may be too small to affect the recipient tree’s growth or survival. Whether the transfer is “sharing” (intentional, cooperative) or a by-product of the fungal network’s own metabolism (the fungi move carbon for their own purposes, and some reaches neighbouring trees as a side effect) is not resolved by the experimental evidence.

The “mother tree” concept has been pressed on its teleological language. Simard describes mother trees as “nurturing” their offspring and “investing” in the network — language that implies intention and purpose. Whether trees are agents with something analogous to purpose, or whether the patterns of resource transfer are better described as evolved responses to environmental signals without any agentive character, is a philosophical question that the ecology cannot settle. The popular reception has tended toward the agentive reading; the scientific community is more cautious.

The forestry policy implications — that clear-cutting and monoculture plantations are counterproductive because they destroy the mycorrhizal network — are plausible but not fully established. The correlation between intact networks and successful regeneration is well-documented in Simard’s fieldwork, but the causal mechanism (is it the network that matters, or the soil conditions, canopy shade, and microbial community that the network is correlated with?) is harder to isolate. Forestry policy based on the network model would require leaving hub trees standing and maintaining species diversity — practices that some jurisdictions have adopted on the basis of Simard’s work, and that others regard as premature given the state of the evidence.

Key works

See also: Margulis · Darwin · Kropotkin · Complex Adaptive Systems · Mutualism