Do Trees Have Memory? Plant Neurobiology and the Phenomenon of Forest Intelligence
Do Trees Have Memory? Plant Neurobiology and the Phenomenon of Forest Intelligence
Trees don’t have a brain. They lack neurons, synapses, or a hippocampus — the region of the brain associated with memory in mammals. And yet, they display phenomena that meet the functional definition of memory: lasting changes in behaviour or physiology based on past experiences.
Just a few decades ago, asking “do trees have memory?” might have sounded like a poetic metaphor. Today, it’s a valid question in a growing scientific field: plant neurobiology. While not dealing with a brain in the conventional sense, researchers are discovering how plants:
perceive and process environmental stimuli,
adjust their behaviour in response to repeated conditions,
“remember” stress events — and can even transmit that information to their offspring.
This is a different model of biological intelligence — not centralised in one organ, but distributed throughout the plant’s structure, supported by chemical signals, electrical impulses, and epigenetic changes.
In this article, we’re not suggesting that trees “think like humans”. But we will explore their own form of intelligence — deeply rooted in time, memory, and interaction with the surrounding ecosystem.
Because perhaps forests don’t remember less than we do.
They just remember differently.
Stress Memory – How Plants Learn to Survive
Memory in plants does not rely on conscious recall, but rather on persistent biological changes that remain even after the stimulus has passed. A tree that has endured drought, disease or intense sunlight may respond more quickly, effectively and efficiently when facing similar conditions again. This is known as stress memory.
Plant Epigenetics: Information Written on Genes (But Not in DNA Itself)
One of the main mechanisms behind this memory is epigenetics — changes in gene expression that don’t alter the DNA sequence, but instead influence how that information is used.
For example, a plant may:
add methyl groups to specific parts of its DNA, silencing certain genes,
rearrange its chromatin structure to make certain genes more or less accessible,
activate microRNAs that block the production of specific proteins.
These changes can persist over long periods of time, and in some cases, be inherited — giving the next generation an adaptive advantage in similar environmental conditions.
Examples from Research
Arabidopsis thaliana, a model plant species, exhibits epigenetic changes after repeated exposure to drought that improve water regulation in leaves and roots.
Scots pine (Pinus sylvestris) growing in dry, nutrient-poor soils express different immune-related genes than genetically identical trees in moist areas.
Some plant species have been shown to “remember” the temperatures experienced by their seeds, which influences when they flower, even months later.
Environmental Memory as a Form of Adaptation
A plant that has experienced environmental stress is no longer the same.
Its metabolism, growth patterns and energy priorities are altered.
This is a form of learning — not conscious, but adaptive.
You could say every tree is a library of environmental experiences, helping it not only to survive, but to live more wisely.
Brainless Plants, But with Decision-Making Networks
Plants don’t have a nervous system — yet they can analyse stimuli, process information and make decisions. How is that possible?
It turns out that internal communication in plants relies on three main “information channels”:
chemical signals (phytohormones, reactive oxygen species, salicylic acid, ethylene),
electrical impulses (transmitted across cell membranes),
hydraulic signals (changes in pressure and water movement).
Each of these systems works at a different speed and on a different scale, but together they form a functional information network — decentralised but highly efficient.
Phytohormones: The Plant “Neurotransmitters”
Instead of neurons, plants use molecules that perform similar roles to neurotransmitters in animals. Examples:
Auxins – regulate growth and the direction of shoots in response to light and gravity,
Gibberellins – control development and ripening,
Abscisic acid – signals drought, causing stomata to close,
Jasmonates – trigger defence mechanisms against pests and pathogens.
These compounds operate with high precision and specificity — just like neurotransmitters, but across plant tissues.
Electrical Impulses: A Rapid Response System
In response to injury, touch or stress, a plant can generate an electrical impulse (action potential), which:
travels through the phloem and xylem,
activates metabolic changes in distant parts of the plant,
can be amplified or modified at “decision points” such as stem junctions.
It’s a system similar to animal nerve function — but without neurons or axons, and based on membranes and internal water channels.
Decision-Making Without a Brain? Yes — But by Different Means
While plants have no “central processor,” they make decisions based on complex analysis of local signals:
Should growth continue or pause?
Is it time to invest in reproduction?
Should defensive chemicals be activated?
Each organ (leaf, root, shoot) is semi-autonomous, but the plant shares and synchronises information across its entire system.
This represents another model of intelligence: distributed, adaptive and effective.
Plant Plasticity – Behaviour That Changes
Plants are often seen as passive or unchanging organisms. However, they demonstrate remarkable behavioural plasticity — the ability to alter their responses depending on context, prior experience, and environmental conditions. This very plasticity is what brings them closer to the concept of learning.
Habituation and Sensitisation – Learning in the Plant World
In animal neurobiology, habituation is the process by which an organism stops responding to a repeated, non-threatening stimulus. Plants do this too.
Example: Mimosa pudica, the plant that folds its leaves when touched.
In an experiment (Gagliano et al., 2014), mimosa was subjected to repeated, gentle mechanical drops. Initially, it reacted by folding its leaves. But after several repetitions, it stopped reacting, conserving energy. Remarkably, the plant retained this “decision” even after several days without stimulation.
Conversely, sensitisation occurs when a plant increases its responsiveness — for instance, activating its defences more rapidly following a previous pest attack.
The Pea and the Light Experiment
In a well-known study (Gagliano et al., 2016), pea seedlings were placed in Y-shaped tubes.
In one branch, light was turned on; in the other, air was blown through.
After a number of repetitions, the plants began growing toward the airflow, anticipating that the light would follow.
This suggests something more than just an automatic reaction — it’s a form of associative learning, the basic principle behind conditioning in animals.
Plants Shift Strategy Over Time
A plant that spends extended time in shade adjusts its priorities: it reduces root development, elongates its stem, increases leaf surface area.
But if the shade disappears, it readjusts and returns to a more balanced growth pattern.
This is not simple reaction — it is strategic resource management, geared towards adaptation.
Communication + Memory = Collective Intelligence?
If a single plant can remember, learn, adapt, and respond — what happens when hundreds or thousands of plants are linked in a living network?
That is the question behind research into mycorrhiza — a fungal network that connects plant roots and forms what is often referred to as the “Wood Wide Web”.
Shared Forest Memory
Mycorrhizal networks do more than transport water and nutrients. They also transmit information about threats, stress and environmental changes.
These signals can be amplified or dampened,
They are sometimes sent selectively, for example to related plants,
They can persist in fungal systems that survive for centuries.
This points to a form of collective forest memory — not stored in brains, but embedded in relationships.
Do Plants Make Group Decisions?
Studies in natural forests have shown that ecosystem responses are not always just the sum of individual tree reactions:
after a fire, some trees slow their growth or expand their roots — not randomly, but based on information circulating in the network,
some plants “give way” to pioneer species, temporarily limiting their own development,
ecological succession seems to progress toward greater stability, as if the system “knows” where to go.
This is not “will” or “consciousness”, but rather a system that learns, adjusts, and remembers collectively.
Different from Animal Swarms? Yes
Collective intelligence in animals (like ants or fish) is based on the coordinated behaviour of individuals.
In plants, there is no movement. What exists is a chemical network of signals, with:
continuity across generations,
no central command,
the transmission of information through space and time,
influence over the structure of the entire ecosystem.
This represents a new kind of intelligence: a collective environmental awareness built on silent cooperation.
Philosophical and Ethical Consequences – If Plants Are Intelligent, What Next?
If we accept that plants — especially trees — are capable of remembering, communicating, adapting, and making decisions, then a crucial question arises:
do they have an interest we ought to consider?
Until recently, law, ethics and economics treated plants as passive resources — components of the environment to be manipulated at will. But plant neurobiology, much like animal ethology before it, is now challenging that view.
Is Conscious Forestry Possible?
If trees remember droughts, warn one another and maintain active underground networks,
if mycorrhiza functions as the ecosystem’s memory and nervous system,
then decisions about felling, replanting or forest management can no longer be purely technical.
Modern forestry must take into account:
the continuity and integrity of mycorrhizal networks,
the role of mature trees as “environmentally aware” individuals,
the fact that a forest cannot simply be “recreated” from scratch if its biological memory is destroyed.
Can Plants Be Ethical Subjects?
This question is gaining ground — in agriculture, biotechnology and urban planning.
Is burning grasslands, pruning or spraying pesticides just a neutral action, or an interference with living beings capable of integrating information and acting accordingly?
Environmental philosophers like Arne Næss and Val Plumwood have proposed expanding ethics to include ecological subjecthood — the recognition that certain organisms (or systems) deserve protection for what they are, not only for what they provide.
New Definitions of Life and Consciousness
Perhaps what we have called “intelligence” — quick thinking, planning, decision-making — is just one of many ways of existing in the world.
Plants act more slowly, through dispersed signals and logic of their own. But their adaptation is no less sophisticated.
Is that enough to speak of consciousness?
Not in the human sense.
But perhaps it’s time to create new categories: distributed awareness, ecological intelligence, biological memory — to help us better understand, not just manage, the natural world.
Trees don’t have brains. They don’t think like we do. But they are capable of remembering, anticipating, reacting — even learning, in their own way, deeply rooted in biology.
Plant neurobiology teaches us that intelligence doesn’t have to be fast or spectacular.
It can be quiet, decentralised, systemic.
Instead of relying on neurons, it operates through chemical messengers, electrical impulses, and environmental memory embedded in DNA and mycorrhizal networks.
If we accept that a forest is not just a collection of trees, but a living system with memory, communication and decision-making, then our way of seeing it — and our responsibility — must change.
It is not enough to protect the surface.
We must understand the depth: the relationships, the networks, the living processes.
Because trees may not have a voice.
But they do have memory.
And we — a duty not to ignore it.
