Imagine walking through the Western Ghats after the monsoon. The soil is damp, leaves glisten with rain, and tiny saplings grow in the shade of towering trees.
Each tree seems to live a life of its own, reaching towards sunlight. Yet beneath your feet, another world is at work.
Tiny fungal threads spread through the soil, forming partnerships with tree roots. They help trees find water and nutrients, while the trees provide them with food. Some fungal threads may even connect neighbouring plants.
This hidden world has earned a nickname: the ‘wood wide web’. But can trees really share resources through it? And what might these underground relationships tell us about protecting forests?
The surprising give-and-take beneath tree roots
Trees use sunlight to make sugars through photosynthesis. But getting essential nutrients from the ground is another matter.
That is where fungi come in. Their microscopic threads reach into tiny spaces in the soil that tree roots cannot easily explore. They help plants take up nutrients such as phosphorus and nitrogen, and can also improve access to water.
In exchange, trees supply the fungi with carbon-rich sugars. Scientists call these partnerships mycorrhizal associations. The name may be unfamiliar, but the arrangement is simple.
The fungal threads, known as hyphae, can spread through soil to form a larger web called mycelium. Some fungi associate with several plants at once, potentially linking their roots in what researchers call common mycorrhizal networks.
The links are intriguing. What is less certain is whether they regularly allow one tree to support another.
Fungi extend through the soil as microscopic filaments called hyphae. Collectively, these filaments form a network known as mycelium. Photograph: (Kabir Gabriel Peay;Advanced Science News)
How scientists began mapping the wood wide web
In 2019, an international team of researchers, including scientists from Stanford University and ETH Zurich, set out to understand where different tree-fungus partnerships occur around the world.
They analysed records from more than 1.1 million forest plots across over 70 countries, covering upwards of 28,000 tree species. With the help of computer models, they mapped the distribution of major types of tree-root partnerships, including those involving fungi and nitrogen-fixing bacteria.
The study, published in Nature, showed that these relationships vary with climate. In cooler regions, for instance, the way dead leaves and other organic matter break down can influence which fungal partners thrive.
The findings revealed global patterns beneath the forest floor. They also raised questions about how changes in temperature and rainfall could affect the partnerships on which trees depend.
Importantly, the scientists mapped broad patterns of association. They did not trace individual fungal threads linking particular trees.
Do older trees help younger ones?
Perhaps the most captivating idea linked to the wood wide web is that of a ‘mother tree’: a large, older tree that nourishes nearby seedlings through shared fungal connections.
Picture a tiny sapling struggling for sunlight beneath a thick forest canopy.
Studies have found that materials can sometimes move between plants associated with fungal networks. But observing movement does not automatically show that a mature tree deliberately helps a seedling, or that the transfer makes the younger tree healthier.
In 2023, researchers reviewed studies of common mycorrhizal networks in Nature Ecology & Evolution. They warned that some popular claims had travelled further than the evidence. In particular, they found no published peer-reviewed evidence that mature trees preferentially send resources or warning signals to their own offspring through these networks.
So the underground partnerships are real. The popular picture of forests acting like families that look after one another remains unproven.
What happens when forest soil is disturbed?
Think of the rainforests of the Western Ghats, the sal forests of central and eastern India, or the mountain forests of the Himalayas. Their climates, soils and trees differ, and so do the organisms living around their roots.
The 2019 global study offers clues about where different partnerships might occur. It cannot tell us exactly which trees are connected beneath any particular Indian forest.
That is why studying local soils and fungi matters. Forest health depends on far more than what grows above ground. Underground organisms help trees obtain nutrients, support the recycling of organic matter and influence how plants respond to changing conditions.
When forests are cleared or soils disturbed, these relationships can be disrupted too. Understanding them could help scientists think more carefully about restoring degraded land and protecting existing forests.
The next time you walk among trees, consider the soil beneath them. Hidden there are thousands of living connections, doing essential work even as scientists continue to uncover how they function.
Protecting a forest begins with understanding the life we can see, and the life we cannot.
