The trunks and leaves of trees you see only begin to tell the story. What you can’t see are the underground roots, make up a vast and complex interconnected system. Though these roots are not connected to each other themselves, they are joined into a network by fungi. This creates a system of connectivity among tree roots that enables trees to communicate with each other and share information and resources.
A tangled web underfoot
Tree roots and this underground system of connectivity all rely heavily on mycorrhizal networks. These are networks of fungi living beneath the surface, connecting tree roots to each other. The mushrooms that you see growing in a forest represent only a small part of the fungus - its fruiting body, or reproductive structures. The rest of the fungus is underground, made up of threadlike structures called mycelia. In some species of fungus, these mycelia colonize and link the roots of two or more trees. Scientists Suzanne Simard and Daniel Durall have summarized the many roles of mycorrhizal networks, which allow trees to transfer nutrients such as carbon, nitrogen, phosphorus, or water among themselves.
What do these connections do?
Mycorrhizal networks enable trees to do many things. Researchers at the University of British Columbia have shown that mycorrhizal networks enable “hub trees” to pass nutrients to smaller trees and seedlings. Hub trees play a crucial role in the overall connectivity and nutrient distribution in tree communities. Hub trees are larger trees who are able to transfer nutrients through mycorrhizal networks, via their roots to help smaller trees. Seedlings often receive nutrients and resources from these hub trees through mycorrhizal networks.
A related study showed that that the size of the hub tree was inversely related to the amount of carbon transferred to seedlings. Seedling survival tended to be greater, and water stress lower, where seedlings had full access to the mycorrhizal network. This shows how mycorrhizal network is crucial for seedlings to access the resources they need to growth and survive.
So next time you are walking in the forest, think to yourself how the trees around you are actually connected to one another deep underground, and depend on one another for survival.
Teste, F. P., Simard, S. W., Durall, D. M., Guy, R. D., Jones, M. D., & Schoonmaker, A. L. (2009). Access to mycorrhizal networks and roots of trees: importance for seedling survival and resource transfer. Ecology, 90(10), 2808-2822. http://www.jstor.org/stable/25592815
Teste, F.P. & Simard, S.W. Oecologia (2008). Mycorrhizal networks and distance from mature trees alter patterns of competition and facilitation in dry Douglas-fir forests, 158, 193-203. doi:10.1007/s00442-008-1136-5.
Simard, S. W., & Durall, D. M. (2004). Mycorrhizal networks: a review of their extent, function, and importance. Canadian Journal of Botany, 82(8), 1140-1165. doi:10.1139/b04-116