Mother trees and the plant-fungi network

I found multiple articles this week talking about how plants (trees, in particular) are connected with one another through their connections with fungi (usually referred to as mycorrhizal networks, and also called the “wood-wide web,” because it facilitates communication as well as transportation of nutrients). I’ve read about this before, but it never stops blowing my mind with how amazing it is. One piece I found a while ago talking about plant-fungi associations mentioned that almost all plant species appeared to have at least one fungus associated with them, that they rarely grow in isolation. I’ve wondered just how healthy plants are when we grow them in places far removed from their native area, or whether they form associations with local fungi . . . Of course I know even many houseplants can live for many many years, without being part of networks like that, isolated from other plants and fungi by being in pots, and apparently they stay healthy enough to live for decades at times, but I wonder what impact it actually has on them, being disconnected from circumstances under which they evolved.

Apparently there’s some evidence that when big trees are cut down in forests, that has a negative impact on seedlings in the area:

Simard’s research has shown that without “Mother Trees” — the big trees that dominate forests and are connected to all other trees — efforts at regeneration often fail. Her latest results reveal that when a Mother Tree is cut down, the survival rate of new seedlings is very low. (source)

Suzanne Simard is an ecologist at the University of British Columbia, and has published research in Nature (which I haven’t looked up yet) about mycorrhizal networks.

Another article had this to say (it’s a terrific piece, with a great graphic demonstrating how complex even a small portion of the connections between trees, made via fungi, are):

Water and sugar have already been shown to move from older trees into the mycelial network (they are feeding the fungi, after all), so it’s possible including young trees in the network helps establish them by providing them with food while they are still trying to stand on their own two feet; indeed, this has been demonstrated experimentally before. You can also see what this implies about only cutting the biggest trees in the forest — doing so greatly diminishes the connectedness and hence resilience of the network.

To my surprise, I discovered when researching this post that it has also been known for a while that trees of different species can communicate with and support one another via their mycorrhizae. . .

In trees, Simard and graduate students Brendan Twieg and Leanne Philip found that Douglas-fir seedling and paper birch shuttle carbon back and forth to one another seasonally via their ectomycorrhizae. Paper birch send carbon to Douglas fir seedlings, especially when they were shaded in summer, probably enhancing their survival. In spring and fall, the Douglas-fir return the favor when the birch have no leaves.

The article also describes an experiment involving Douglas-fir and ponderosa pine seedlings, which were isolated in such a way that only fungi could connect them, and found that under stress, nutrients moved from the Doug-fir to the pine. What the exact mechanism is that’s prompting this is uncertain:

Did the douglas-fir “intentionally” and altruistically send food and defensive signals to the ponderosa pine, or did the fungus act to take them there? It’s possible that it is only passive effect of a source-sink scenario, where the douglas-fir dumped food into its mycorrhizae for safe-keeping in light of severe stress, and the excess resources simply moved from an area of high concentration to an area of low concentration (the growing, resource-hungry ponderosa pine). It’s also possible the douglas-fir is behaving somewhat altruistically and somewhat pragmatically, since exporting carbon to its root network may benefit nearby trees that are close relatives (offspring, even?), and any spillover to trees of completely different species that keeps them healthy may also benefit these same relatives by keeping the forest system as a whole healthy.

It’s also possible the fungus played the more calculated role of a broker with its own interests and “acted to protect its net carbon source,” write the authors, “by allocating carbon and signals to the healthy, more reliable ponderosa pine.” In this way, mycorrhizal fungi may help forests be more resilient to assault in general but especially to those from climate change — whether from drought or pest attacks. In this way, they would help transfer existing, hard-won food resources and insect warning signals from species dying out due to changing climate to species migrating northward into newly vacant habitat and struggling to get a toehold.

Regardless of the process, it’s clear that individual trees aren’t as “individual” as they first appear, the health of one tree can literally be affected by the health of other trees around it, and that modern forest “management” that involves logging to “improve” the health of a forest probably needs to take a lot more into consideration than there is any evidence is being done.


About Fjothr Lokakvan

More or less Northern Tradition polytheist.
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