The Wood Wide Web

Tim Iverson

(11/2016) Imagine yourself in a forest. Within this grove you’re liable to see trees, shrubs, birds, mammals, and more. At the base of this, or any given forest, is a thin layer of substrate. Lining all forest floors is a tangle of woody and leafy debris that accumulates over time. On the surface, if you look closely enough, you’ll discover tiny decomposers - mainly insects whose job it is to clean this perpetually building mess. Decomposers come in all forms: insects, slugs, molds, fungi. The decomposers consume all the accumulated leafy and woody material and excrete the nutrients out so the forest can continue to grow upwards and outwards. One of the most important agents in this cycle is the one often unseen - the fungus, mycelium. Extending vastly under the soil, surfacing just at the bottom of leaf litter are barely visible thin white threads. This is just the tip of the iceberg. This fungal network, the mycorrhizal network, is an internet - a wood wide web.

It starts with the hyphae of fungus spreading out across the forest floor. Hyphae is a white filament that looks similar to thread or string, and is collectively called mycelium. The hyphae spurs vegetative growth for fungi, and is the first principal agent in breaking down all those leaves and other things in the detritus litter. Enzymes are secreted from these which breaks down the dead plant material, then nutrients are absorbed and carried throughout the body of the fungus. It’s a lot like chewing and swallowing.

As this network of mycelium spreads out across the forest floor it connects with other mycelial networks, plants, shrubs, and trees. This interconnected expansive network is called the mycorrhizal network, or more commonly "the wood wide web." Just like the internet is the information superhighway, this wood wide web functions in a similar way. This network collects, transfers, and shares resources such as water, nutrients, and minerals to connected plants and trees across the network. It even appears to act like a banker or resource broker in some instances, and more incredibly as a communicator sharing information between individual organisms within a population.

Like any good banker or broker this exchange comes with a fee. The fungus wraps around and connects itself to the roots of trees and plants. Trees are good at producing sugar, this is where syrup comes from after all. They use some sugar to grow, but the rest is banked or given to the fungus. In exchange the fungus provides the tree with necessary water, carbon, phosphorous, and other nutrients and minerals. Dr. Suzanne Simard conducted an experiment to test this underground economy and network. She took three different species of tree within a single stand, sealed them in plastic, and sprayed them with a radioactive isotope. They absorbed these isotopes through photosynthesis and then she tested neighboring trees outside of the stand. Outside of the initial 30m by 30m plot other trees were testing positive for the radioactive isotope. After extensive mapping her research showed that a single tree can be connected to as many as 47 other trees (including trees of the same and different species).

Her argument is that a forest is more akin to a superorganism, like a colony of bees. Our traditional view is that trees act as a single organism competing for resources, but this appears not to be the case. Each individual is connected into this fungal network and sends and receives food and resources to each other. In times of abundance they share and bank resources, in times of hardship they can make withdrawals. A German forester, Peter Wohlleben, released a book (The Hidden Life of Trees) that describes a stump from a tree harvested approximately 400 years ago. What is remarkable about this stump is that it is growing and continually adding new tissues and layers. Without leaves to photosynthesize and create sugar this growth would be impossible. His explanation is that this stump was being supported by its neighbors. This mycorrhizal network is like a neurological social network sharing resources and information to those who need it.

When a tree or a plant gets eaten by animals and insects it attempts to defend itself. It sends electrical and chemical signals to other areas of the tree to start producing allelochemicals, which are foul tasting, in order to discourage the attacker. These chemicals and signals are then picked up by neighboring trees of similar species so they can begin their defense. A well known example of this is with Acacia trees in Africa. Giraffes feast on the leaves, the tree produces these chemicals which are very acidic and cause severe indigestion and can even poison an herbivore in high concentrations. Surrounding trees get the message and start producing these chemicals as well. The giraffe, however, has caught on to this and will bypass two, three, or four surrounding trees before beginning his buffet again in order to avoid this defense mechanism.

Resource exchange has been well documented to occur as seasonal exchanges too. Birch trees are documented as transferring carbon and other resources to Douglas Fir during the summer months when they are surrounded in shade by the taller groves. In the late fall and early spring the pines return the favor by shifting resources back to the birch. When a tree dies or an old stand is doing poorly for extended periods of time they have been documented to dump their resources into the network. In a final last act or dying gasp they will their sugars and nutrients into the wood wide web. Interestingly, these resources don’t seem to go to trees of the same species. Research appears to show that these resources are reallocated to younger trees who are better adapted to harsher conditions. For example, in the western United States Dr. Simard has documented that Douglas Fir is sending resources to Ponderosa Pine. The Douglas Fir isn’t well adapted to the increasing effects of climatic changes that are ongoing, but the Ponderosa Pine is well suited for these conditions. By exporting carbon and other nutrients to the Ponderosa Pine the forest as a whole is stronger.

The question at large among botanists, foresters, and researchers alike is mostly a matter of intelligence. Science has proven these exchanges are occurring in the mycorrhizal network. What remains to be seen is to what extent does this network act as a broker. Is it simply an economic exchange or does it help to allocate resources to where it can be best used? One can not simply walk away from this evidence thinking as trees as solitary stoic islands, but rather as intricately interwoven into the social network of the wood wide web.