Facts in «The Other Half»
The claims in the narration, their sources, and how the film words what is still open. The trees, roots, soil and grains are illustrative.
| Claim in the film | Source | Note |
|---|---|---|
| "Do the trees in a forest feed each other?" | A widely repeated popular claim (the "wood wide web", "mother trees" feeding seedlings). | Asked as a question; the film does not assert it. |
| "A tree's finest roots are wrapped in fungus" | S. E. Smith & D. J. Read, Mycorrhizal Symbiosis, 3rd ed., Academic Press (2008). Most land plants form mycorrhizas: M. C. Brundrett & L. Tedersoo, "Evolutionary history of mycorrhizal symbioses and global host plant diversity", New Phytologist 220, 1108–1115 (2018). | Ectomycorrhizal fungi sheath fine root tips; arbuscular fungi grow into the root's cortex. The picture shows a sheath and threads fanning into the soil. |
| "threads far thinner than a hair" | Fungal hyphae are typically about 2–10 µm across (Smith & Read 2008); a human hair is about 50–100 µm. | |
| "The tree pays the fungus in sugar, made from sunlight" | Smith & Read 2008. Arbuscular mycorrhizal fungi also receive lipids: A. Keymer et al., "Lipid transfer from plants to arbuscular mycorrhiza fungi", eLife 6, e29107 (2017). | "Sugar" simplifies plant carbon. |
| "The fungus pays back in water and nutrients from the soil" | Smith & Read 2008 (phosphorus and nitrogen above all, and water). | Shown as blue-green grains returning to the root. |
| "And the same fungus can reach the next tree" | K. J. Beiler, D. M. Durall, S. W. Simard, S. A. Maxwell, A. M. Kretzer, "Architecture of the wood-wide web: Rhizopogon spp. genets link multiple Douglas-fir cohorts", New Phytologist 185, 543–553 (2010). | One fungal individual mapped on several trees. |
| "Whether trees pass food along it is still argued over" | J. Karst, M. D. Jones, J. D. Hoeksema, "Positive citation bias and overinterpreted results lead to misinformation on common mycorrhizal networks in forests", Nature Ecology & Evolution 7, 501–511 (2023). | The film draws no sugar crossing from tree to tree: the sugar is taken up by the fungus halfway, and the tree-to-tree path is a dashed line with a question mark. |
| "No tree grows alone" | Brundrett & Tedersoo 2018 (the great majority of land plants live with mycorrhizal fungi). | A summary in words, not a measurement. |
| Soil horizons (leaf litter, topsoil, subsoil, weathered rock, bedrock) | USDA Natural Resources Conservation Service, "Soil Horizons" (O, A, B, C, R horizons). | Drawn without labels in the film. |