The Secret Language of Trees

Earth is home to around 1 trillion trees that belong to over 60,000 species and they live on every continent but Antarctica where trees have actually been around for close to 400 million years where they’ve survived all four extinction events that they’ve been around for where their ability to break down rocks create soil and siphon carbon dioxide from the air and replace it with oxygen is what made our planet habitable for humans.

In 1885 German botanist Albert Bernard Frank first proposed the idea that plant roots and the fungi around them were working together and like with many bold scientific assertions he was basically laughed out of the room but in the last century nearly all of Frank’s major hypotheses have been unequivocally demonstrated.

We now know that plant and fungal associations known as mycorrhizal associations are present in almost all ecosystems from deserts to tropical forests and that about 90 percent of terrestrial plants are connected to some form of mycorrhizal fungi network.

The most common fungal networks are made of arbuscular mycorrhiza which are named for the Latin arbiscule meaning little tree where the threads of this fungi penetrate the root cells of their host and form tiny structures inside of them where this is how they interact with the trees and share resources with them.

The other major class of fungi are ectomycorrhizal fungi where these fungi form a sheath around the roots of their hosts and grow between the plant cells to exchange nutrients where they have a symbiotic relationship with fewer plants than the arbuscular mycorrhizae but their hosts tend to be the most economically important trees as they are often the most widespread trees that we use for timber.

The fungi pick up water and nutrients from the soil including phosphorus and nitrogen which are both important for plant growth and transfer them to their plant hosts where in return the plants transfer their fungal friends between four and twenty percent of their photosynthate the sugars they produce by photosynthesizing where this relationship is the backbone of all our forests on Earth and without it life on land as we know it may have never emerged.

The first inkling that trees might actually work together came in a study in the early 1980s where scientists planted pines side by side in a box then inoculated their roots with mycorrhizal fungi then they tagged the photosynthetic sugars produced by the donor pine with radioactive carbon where they did this by sealing one plant in a box with radioactive carbon dioxide where they then allowed the pine to absorb it and convert it into radioactive sugars through photosynthesis then they placed photographic film over the side of the root box hoping to see where the radioactive particles traveled where when they developed the film they saw the path that the charged particles had taken and the path was through the mycorrhizal fungal network traveling from one tree to the other.

Researcher Suzanne Simard looked at nutrient exchange between Douglas fir trees and paper birch trees two different species where she planted fir birch and cedar seedlings in a trio where she labeled the paper birch with the radioactive isotope carbon-14 and labeled the Douglas fir with a stable isotope carbon-13 that way she could tell not only if carbon was moving from birch to fir but could tell if it was moving from fir to birch where the cedar plants acted as a control where cedar can’t form mycorrhizal networks with the fir or birch because it forms arbuscular mycorrhizae not ectomycorrhizal like the other two where she then covered the fir with a shade tent reducing photosynthesis where what she found was that the birch and fir trees indeed share resources where in fact the more shade the fir was covered by the more carbon-14 it received from the birch and the cedar did not receive either of the isotopes.

Other experiments have looked at the chemicals trees produce to signal that they’re being damaged where one experiment looked at tomato plants all linked up through an arbuscular mycorrhizal network where when the researchers infested some of the plants with leaf-chewing caterpillars healthy neighbors had activated four defense-related genes within 6 hours where in other words they knew trouble was coming and they were preparing for it where the plants that had time to produce defensive enzymes against the pests fared better and the caterpillars munching on those second plants didn’t grow as large.

There’s also evidence that trees of the same species have some form of kin recognition through their fungal networks where they can identify which trees are most closely related to them and direct more resources towards those trees.

In her research Suzanne Simard and her team found that the biggest oldest trees what are called the mother trees are the hubs of these below ground fungal networks where they are the most connected nodes in the network of the forest where mother trees share their excess carbon and nitrogen through the mycorrhizal network with the understory seedlings which can increase seedling survival where in a single forest a mother tree can be connected to hundreds of other trees.

The problem is this we’re great at clear cutting and great at clear-cutting mother trees where we always either log the entire forest or go for the biggest oldest trees because they’re the most valuable but if too many of these mother trees are logged too many of the nodes removed the forest as a whole will start to decline where disease can start to spread and insects start campaigns of destruction.

With this research hopefully a shift can start to happen where understanding that trees in a forest are connected underground to their kin and to their neighbors could change the way trees are logged where when forests are harvested the retention of mother trees can provide resilience where smaller hope trees can be removed without causing the network to collapse where leaving enough hub trees and enough of the mother trees within the network allows for the flow of communication and the trading of resources to continue where retaining mother trees can also help the forest regenerate where seeds from the mother tree will sprout nearby and are able to quickly tap into the mycorrhizal network and receive resources from their community that boost their chances of survival.

Researchers are now investigating how the connections between mother trees seedlings and other plants enhance resilience of the forest community where maintaining the network of connections between trees in a forest should help them resist the stress of climate change and recover more rapidly when climate-related disturbances do occur where connected forests are better able to cope with climate change and be more productive healthy and diverse.

Scientists are looking for ways to utilize it not just in the forests but in our agricultural fields where the majority of staple food crops are known to form relationships with mycorrhizal fungi if the soil is in good enough condition for the fungi to flourish where these fungi could provide crops with nitrogen and phosphorus which means the farmers wouldn’t be so reliant on fertilizer where it could be a natural scalable and elegant solution to chip away at the damage agriculture causes on the planet.