Electrode pair
Two identical electrodes, one in the xylem region of a living tree and one in the surrounding soil. Identical materials keep a dissimilar-metal reaction out of the measurement.
Technology
Reading the electrical signal of a living tree
A tree maintains a measurable electrical potential against the soil it grows in. That potential has been documented and its mechanism published. VoltreeAI builds sensors that record it continuously, in the field, under the canopy.
Forest floor, electrode placement at the root collar
The physical basis
A concentration cell, driven by pH
In 2008, researchers at MIT reported sustained differences of 50 to 200 millivolts between the xylem region of an intact tree and its soil, using identical platinum electrodes to exclude a simple dissimilar-metal reaction.
They attributed the potential to a biological concentration cell driven by the pH difference between the tree and its soil. The research was funded by Voltree's founders.
Sustained voltage differences of 50 to 200 mV were recorded between the xylem of intact trees and the surrounding soil, with identical electrodes at both terminals.
PLoS ONE, 2008
The instrument
What the sensor does
Connectivity
Battery-first by design. Each node stores its readings and forwards them at low power to a gateway. Voltree built one of the first under-canopy radio networks in 2009 and learned from it: harvested power alone could not sustain reliable meshing in remote forest. The current architecture is therefore battery-first, with energy harvesting in evaluation as an assist, and LoRaWAN or cellular backhaul under test for large sites. Range and node density: in development.
Energy harvesting and backhaul: in evaluation · Range and node density: in development
Data pipeline
Readings arrive with a timestamp, a node identity and local conditions, and are served through an API with configurable threshold alerts.
API specification in development
Siting
Under canopy against open clearing
| Weather station in a clearing | VoltreeAI node | |
|---|---|---|
| Siting | Open ground, chosen for exposure and access | Under the canopy, at the base of a living tree |
| Measured quantity | Air temperature, humidity, wind, precipitation | Electrical potential between xylem and soil |
| Relationship to fuel | Fuel moisture is estimated from a weather model | Measurement taken at the fuel itself |
| Cadence | Interval reporting, typically hourly | Continuous sampling |
Comparison
Against the alternatives
| Method | What it measures | Under the canopy? | Character |
|---|---|---|---|
| Weather stations | Air temperature, humidity, wind — in open clearings | No | The reference network fire danger is modelled from |
| Manual fuel sampling | Gravimetric fuel moisture — the reference standard | Yes | Point measurements, labour-bound, not continuous |
| Satellite fuel-moisture products | Canopy-top moisture index | No | Broad coverage, coarse resolution, multi-day timing |
| In-forest sensor networks | Air temperature, humidity, smoke and gas | Yes | Continuous, at node level |
| Voltree.ai | Tree–soil potential plus node microclimate | Yes | Continuous at the tree; relationship to fuel moisture in evaluation |
We are not the only sensor under the canopy. We are testing whether the tree itself is a better instrument than the air around it.
Continuous potential trace, one node, twenty-four hours
Open questions
What we are still establishing
The existence of the potential is settled. Its behaviour as an operational signal is not. These are the questions our validation programme is built around.
Quantitatively, across species and seasons, this is unresolved. It is the primary subject of our current validation programme, and we do not present a correlation we have not demonstrated.
Electrode drift over long installations is a known failure mode for any in-situ electrochemical measurement. We are characterising drift and testing compensation against paired reference sampling.
We are comparing gravimetric fuel moisture sampling, soil water potential and stem water potential to establish which reference the field signal tracks most closely.
Disease, mechanical damage and drought stress all change the physiology behind the measurement. Interpreting a reading requires knowing the condition of the tree it came from, which is part of what we record.
We publish what we find, including results that do not support the hypothesis.