Forests think with their fungi.
Six sections from the underground network to the scientific debate. Click trees, slide thresholds, watch carbon flow between species, then read why the romantic version of the Mother Tree concept has come under serious attack.
A forest is a graph.
Thirty-six trees, two species (Douglas fir, paper birch), connected by two genera of fungi (Rhizopogon, Suillus). Edges are real mycorrhizal connections that Simard traced in 1997 using radioactive carbon. Hover any tree.
A few hubs hold the network together.
Beiler 2010 mapped 67 Douglas firs in British Columbia. The oldest trees (>200 years, >70 cm DBH) had up to 47 connections, the youngest only two. Slide the threshold and watch the hub trees light up — the scale-free signature of a real network.
Four to six per cent of a season's photosynthate moves between trees.
Simard's 1997 ¹³C and ¹⁴C tracer experiment showed that Douglas firs and paper birches exchange carbon through fungal connections. Net transfer goes from the species in sun to the species in shade. The particles follow the actual shortest path through the network you saw above.
More for family than for strangers, sometimes.
Pickles et al. 2017 measured about ten per cent more carbon transfer to kin Douglas fir seedlings than to strangers. Other studies find less, or nothing at all. Move the slider to set a degree of relatedness — the mother on the left responds, the scatter on the right shows what six published studies actually found.
Six studies, six results — hover.
Cut the wrong tree, the network unravels.
Forestry practice often leaves the oldest, biggest trees for seed — but ignores their network role. Click a hub tree to remove it and watch the connectivity collapse. Beiler's hub-removal simulations showed a single big mother tree's loss isolated dozens of seedlings.
Click a tree to remove it from the network.
Honest science is messier than the metaphor.
The Mother Tree concept became one of the most popular images in modern biology. It also became one of the most contested. Karst, Jones & Hoeksema published a forceful critique in Nature Ecology & Evolution in 2023; Simard replied the same year. Both sides have a point.
- Field tracer experiments since 1997 do show carbon transfer between trees via fungi, replicated by several independent labs.
- Hub topology in forest networks is real: a few old trees concentrate the connections, as direct genotyping showed in Beiler 2010.
- Kin-preference effects, while modest, have been measured in controlled chambers; they are biologically plausible if not yet fully mechanistically explained.
- Many cited studies in the field measure that fungi connect trees, not that the connection meaningfully changes plant fitness in forests.
- Citation analysis shows results are systematically inflated as papers cite each other; a positive-result feedback loop, not new evidence.
- The Mother Tree language anthropomorphises a fungal phenomenon. The fungi may benefit; the trees may be neutral or even harmed in some species.
The network exists. Carbon does move. The forest is not a collection of isolated trees. But whether the network is principally a tree-to-tree communication system, a fungal-to-tree resource market, or something more like a passive plumbing system is genuinely unresolved. The honest position right now is: networks yes, motherhood maybe.
The forest is a procedurally generated network of 36 trees with a fixed seed, so every visit shows the same layout. Tree age follows a Pareto-like distribution (most young, few old) and connection count grows roughly with log of age, matching the hub topology Beiler 2010 measured in real Douglas-fir stands. Fungal threads are quadratic Bézier curves drawn under a soil line; carbon particles in section 3 follow the breadth-first shortest path between donor and recipient. Transfer rates and species choices come from the cited papers.
- Simard, S. W., Perry, D. A., Jones, M. D., Myrold, D. D., Durall, D. M. & Molina, R. (1997) — Net transfer of carbon between ectomycorrhizal tree species in the field. Nature 388, 579-582.
- Beiler, K. J., Durall, D. M., Simard, S. W., Maxwell, S. A. & Kretzer, A. M. (2010) — Architecture of the wood-wide web: Rhizopogon spp. genets link multiple Douglas-fir cohorts. Journal of Ecology 98, 538-548.
- Klein, T., Siegwolf, R. T. W. & Körner, C. (2016) — Belowground carbon trade among tall trees in a temperate forest. Science 352, 342-344.
- Pickles, B. J. et al. (2017) — Transfer of ¹³C between paired Douglas-fir seedlings reveals plant kinship effects and uptake of exudates by ectomycorrhizas. New Phytologist 214, 400-411.
- Gorzelak, M. A., Asay, A. K., Pickles, B. J. & Simard, S. W. (2015) — Inter-plant communication through mycorrhizal networks mediates complex adaptive behaviour in plant communities. AoB PLANTS 7, plv050.
- Simard, S. W. (2018) — Mycorrhizal networks facilitate tree communication, learning, and memory. In: Memory and Learning in Plants. Springer.
- Simard, S. W. (2021) — Finding the Mother Tree: Discovering the Wisdom of the Forest. Knopf.
- Karst, J., Jones, M. D. & Hoeksema, J. D. (2023) — Positive citation bias and overinterpreted results lead to misinformation on common mycorrhizal networks in forests. Nature Ecology & Evolution 7, 501-511.
- Simard, S. W., Beiler, K. J., Bingham, M. A., Deslippe, J. R., Philip, L. J. & Teste, F. P. (2023) — Reply to: Positive citation bias and overinterpreted results lead to misinformation on common mycorrhizal networks in forests. Nature Ecology & Evolution 7, 1769-1771.
- Henriksson, N. et al. (2023) — The mycorrhizal tragedy of the commons. Ecology Letters 26, 1264-1278.
- Robinson, D. G. et al. (2024) — Mother trees, altruistic fungi, and the perils of plant ventriloquism. Trends in Plant Science 29, 20-31.