# How would trees communicate?

An alternate world is populated by mainly intelligent trees and other plants. These plants are almost exactly the same, biologically, as Earth's plants. The world's climate and geology are very similar to how Earth would be if intelligent life (other than the plants) had never evolved. Without causing any major changes, would it be theoretically possible for these plants to communicate? And how would it work?

• I appreciate the checkmark, but it is in your best interest to wait a day or two minimum before accepting an answer. This gives more people an opportunity to answer who might not otherwise if they see there is an accepted answer. Jan 6, 2019 at 7:28
• I have to say it : bush telegraph. :-) Jan 6, 2019 at 9:42
• What time frame does communication occur over? What information do they need to communicate? Complex communication comes from a need for complex cooperation, so what are they trying to achieve? Jan 6, 2019 at 10:28
• Good answers below. Here is something else to think about, electrical transmission between plants in contact with each other: ted.com/talks/… Jan 6, 2019 at 17:32
• They would just, like, communicate, man. Feel the world. Feel each other. One big happy family, man. Jan 8, 2019 at 11:09

## Sound

They would produce sounds in one of two ways (probably both)

• By shifting their branches and leaves in just such a way that when the wind blows it makes the sounds they desire. Much like our vocal cords. The drawback is we produce our own wind whereas they would need to rely on air passing through their foliage.
• By creaking. They shift their entire bodies to extremes causing them to make sounds. The added advantage of this is that the young who have "poor language skills" or "developing language skills" are mostly struggling with the fact that they are extremely flexible and don't make a lot of noise as such.

All of these sounds can be detected as vibrations they pick up in their bark or their foliage (or both.)

## Earthly Vibrations

Or perhaps they have the ability to cause vibrations in the ground by wiggling their roots. The other trees can also sense the vibrations through their roots. This would like make it hard to make out more than one "speaker" at a time.

## Chemical Signals

Similar to the way ants communicate. However this would have to be transferred in some way. Perhaps pollen? Then it is more like they write messages in their pollen and wait for the bees to deliver the messages for them.

• You answer is pretty close to the one I was going to give. On another note, have you seen this TED talk about plants transferring electrical signals?:ted.com/talks/… Jan 6, 2019 at 17:35
• Communicating via root vibrations and the associated "too many speakers" problem would give a narrative reason for them to invent Ethernet-style communication. Jan 8, 2019 at 13:09

Plants already communicate, we simply ignore or are just now starting to discover most of the mechanisms they use.

An African tree has been found capable of communicating with its neighbors to warn them about excessive consumption from antelopes, so that they can secrete more tannine. (paper cited below)

Tomatoes communicate using roots: plants growing close to an infected one started producing antibodies against the pathogen. (paper cited below)

Some pines have been found exchanging electric signal, even though they lack neurons. (paper cited below)

Here is a set of scientific papers where you can find more info:

• Baldwin IT, Schultz JC. Rapid changes in tree leaf chemistry induced by damage: evidence for communication between plants. Science 1983;221:277-9.
• Dudley SA, File AL. Kin recognition in an annual plant. Biol Lett 2007;3:435–8.
• Mousavi SA, Chauvin A, Pascaud F, Kellenberger S, Farmer EE. Glutamate receptor-like genes mediate leaf-to-leaf wound signalling. Nature 2013;500(7463):422-6.
• Ramakrishna A, Giridhar P, Ravishankar GA. Phytoserotonin, a review. Plant Signal Behav 2011;6:800–9.
• Robbins CT. Role of tannins in defending plants against ruminants: reduction in dry matter digestion? Ecology 1987;68:1606-15.
• Roshchina VV. Evolutionary considerations of neurotransmitters in microbial, plant, and animal cells. In Microbial endocrinology. Lyte M et al. (Eds), p. 17-52, Springer 2010.
• Simard SW, Beiler KJ, Bingham MA, Deslippe JR, Philip LJ, Teste FP. Mycorrhizal networks: mechanisms, ecology and modeling. Fungal Biol Rev 2012;26:39–60.
• Song YY, Zeng RS, Xu JF, Li J, Shen X, Yihdego WG. Interplant communication of tomato plants through underground common mycorrhizal networks. PLoS One 2010; 5: e13324.
• Van Hoven W. Mortalities in Kudu (Tragelaphus strepsiceros) populations related to chemical defence of trees. Rev Zool Afric 1991;105:141-5.
• Van Hoven W. The tree’s secret weapon. South African panorama 1985;30:34-7
• See also "Crown shyness" en.wikipedia.org/wiki/Crown_shyness Jan 6, 2019 at 10:30
• The roots explanation has been used in sci-fi already, too, probably most famously in the movie Avatar (though I can't find the scene right now). Sigourney Weaver's character comments about the trees communicating like neurons, with more connections than the human brain. Jan 7, 2019 at 22:01
• +1 for the Wood Wide Web. Jan 8, 2019 at 14:45
• Can't find the source right now, but I also recall reading an article about how some crops (eg: corn) can release pheromone combinations to attract various kinds of wasps, to kill other insects currently eating their leaves. They can even call for specific breeds of wasp that hunt specific prey - which also implies they can somehow tell what's (literally) eating them. So, plant communication is not strictly limited to amongst other plants, either. Jan 8, 2019 at 15:07

You don't have to speculate very far at all; it's a widely accepted notion, since Prof. Suzanne W. Simard's 1997 research paper, "Reciprocal transfer of carbon isotopes between ectomycorrhizal Betula papyrifera and Pseudotsuga menziesii" that plants communicate using chemical secretions, primarily through their root systems.

Her team proved this by injecting the root systems with radioactive "tracer" isotopes, the passage of which could be tracked through to the root systems of neighbouring plants. It's become known colloquially within the Plant Sciences domain as the "Fungal Internet".

https://interestingengineering.com/study-reveals-plants-communicate-through-root-secretions

https://e360.yale.edu/features/exploring_how_and_why_trees_talk_to_each_other

When elephants eat the acacia tree, they start down wind because the attacked plant produces toxin as well as pheremones to alert nearby trees so they can start producing toxins.

By starting down wind the elephants can work they way up wind without the trees alerting the other trees

See Alarm Scents

If you want to take it slowly:

Leaves are the mouths
Roots are the ears


So a conversation would involve the tree creating a chemical composition in the leaves to communicate some 'message'. These leaves fall and decompose, with the resultant message being transported through the soil and taken into the roots of another tree.

Naturally, with the dependence on leaf scatter patterns, prevailing winds and distances between trees, such exchanges in conversations take an extremely long time. Hence rather than each leaf containing a single message such as "It's a nice autumn we're having", leaves contain partial messages with a high level of redundancy across the leaves so that a cascade of falling leaves communicates an entire concept or state, in a very similar way as the logograms in the book Story of Your Life (film: Arrival).

As the entire knowledge of one tree can be transmitted in this way, it leads to an accumulation of understanding in large dense forests. Some of which have evolved in ways that would not be expected of 'normal' plant life.

• For being that live centuries and never move, that speed of communication seems adequate.
– ecc
Jan 8, 2019 at 12:36
• @ecc I try to make suggestions that are workable :-) And this could be extended further along the lines of "someone else completing a sentence for you" when one tree is still forming the message so the early leaves contain an indistinct concept, and the receiving tree is forming an indistinct response, and over time the concept and response become better defined and more refined and the constant fall of leaves over that time reflect the evolution of the conversation. A true concord is maybe achieved only once in a tree's lifetime, but what a concord it is! Jan 9, 2019 at 3:31

Since both the communications of plants to warn of pathogenes, predators and to exchange nutriant has been mentionned in previous answers, let's just add that Darwin had speculated about the roots being to plants what the brain is to animals source

“It is hardly an exaggeration to say that the tip of the radicle thus endowed [with sensitivity] and having the power of directing the movements of the adjoining parts, acts like the brain of one of the lower animals; the brain being seated within the anterior end of the body, receiving impressions from the sense-organs, and directing the several movements.”

If we have intelligence then you might want to have settlements, which with network effect multiplies communication. Huge root networks like Pando, the largest organism on Earth would enable very fast communication.

Also, since you mention populated by mainly intelligent trees and other plants, we could assume some form of animals might be present and could have been domesticated for communication when roots or chemicals cannot do it. Based on Earth insects would most likely be domesticated and used for communication, but possibly bigger animals since they are already used on Earth for for seed dispersion on long distances(extract below, source, they could be used on your planet for long distances physical artefacts deliveries.

"large herbivores are irreplaceable as seed dispersers because, relative to smaller frugivores, they are able to consume larger seeds and deliver many more seeds per defecation event over longer distances."

You could do a lot worse than read The Companions by Sheri S Tepper. Too many themes to even start to summarise, but one of the main characters is a sentient plant on a planet of variously-sentient plants. The book puts forward some simple concepts of grammar for a language of emotion-triggering pheromonal scents, and describes that character's perceptions based on its sensory abilities.

The next question after that, of course, is that if plants can communicate with each other, what would they say? Therein lies some of the plot of Tepper's book, and presumably your story will also need to cover that too.

would to communicate in the first place trees have to evolve a brain or equivalent to use that communication, but to communicate i would expect trees to produce a "scent", as Graham said, from flowers if they had them, to stimulate meanings, similar to that of animals marking their territories might produce. Along with transmitting as much information as possible.

Then again communication evolved out of necessity so what do trees need that asks for communication?