Tree times: what trees teach us about time and rhythm (interview)

What is Tree Times?

"For a year, the artists worked with three Scots pines in three nature reserves to design tree clocks. They recorded the trees' movements with sensors that measure the expansion and contraction of the trunk, along with data on CO₂ uptake, air temperature, humidity and sunlight. Although the three trees live in similar biotopes, their internal clocks showed major differences.

This resulted in an installation with three parts: a map that shows the time experience of the trees, diaries that can be requested via SMS, and a web app for those who want to dive deeper into the data. The installation can be seen at De Vroente, Duurzaam Educatiepunt, the De Liereman visitor centre, the Pijnven Forest Museum in Bosland and in Constant's showcase in Brussels."

What was the inspiration behind the project?

"Last year we already worked with similar sensors in Arnhem, for the installation Arnhem Trees Tell. Back then, visitors could look back in time three weeks via an app. We kept an annual record ourselves and discovered that trees have their own rhythm and perception of time. So we decided to measure three Scots pines for a year and compare the results side by side.

The project builds on the idea of criptime, a notion of time invoked by people for whom normative time often does not meet their needs. A working day from 9am to 5pm, a route from A to B that, according to an algorithm, you cover on foot in 10 minutes; but also life events that would take place by default, such as living independently, getting married, having children. This raises questions such as: what experience of time do trees have? When does their sap flow, when do they become active, when do they rest, and when does their trunk increase in size the most?"

You call yourself 'tree registrar'. What does that mean?

"Tree grazier is a word I made up myself. It describes the way I work with trees: I spend time with them while writing, on site or remotely, once the tree has given its consent."

How were the measurements taken and what data were collected?

"The sensors we use largely come from the commercial market. Only the point dendrometer at the Scots pine in Bosland - which measures the speed of sap flow - was developed by UGent (Dr Kathy Steppe) and is managed by them. Thanks to the collaboration with Boslab, we were able to use that data.

The_{CO2 sensors} hung in the crown of the trees are a product of Milesight, a Chinese company based in Xiamen, Fujian province. They are intended for 'harsh' conditions, greenhouses, yard ventilation, fruit and vegetable storage. They measure how much_CO2 is present in the crown, thus measuring much less during daytime photosynthesis.

The soil sensors, developed by Dutch start-up Sensoterra, measure soil moisture and temperature at the roots. They are used for "agriculture and irrigation management, smart cities, water and environmental monitoring. Each tree also received a tape dendrometer, which measures the contraction and expansion of the trunk. It is developed and sold by EMSBrno, a company in the Czech Republic that works closely with universities. The trunk shrinks during the day, when it pushes water to the crown. At night, the trunk refills with water and permanent growth also takes place; then the trunk expands slightly.

The sensors connect to what is called the Internet of Things. For instance, the soil sensors work with LoRaWAN. It has a long range, but can transmit little data. In the case of sensors, this is fine because they record one number every 10 minutes."

Can the data on Scots pine (from the Kalmthoutse Heide) be consulted somewhere?

"Yes, via treetimes.bomenvertellen.net. Select 'Kalmthout' from the 'Show data from' menu.
There you will find an analysis of the data based on the day types recognised by the algorithm. For example, the mild winter of 2024-2025 gave a long winter period with no clear autumn, while summer distinguishes two types of summer days: very warm and moderate."

What is the most surprising thing you learned while observing the trees?

"The technology actually confirms what people already knew in pre-Christian times: trees are perfect guides to understand time, seasons and activities," he says.

Trees register everything in their environment - sunlight, temperature, length of days - and adjust their activity accordingly: when they form buds, bear fruit or lose leaves. The rhythm of their breathing follows the day and night cycle.

By combining different data layers such as trunk movement, sunlight, moon phases and seasons on an artistic map, this ancient insight becomes visible again: trees live according to the rhythms of Sun, Moon, planets and stars.

Maja Kooistra puts it into words in her book Leven met Bomen:

"In a constantly changing world, people were looking for fixed patterns to anchor their lives. They recognised that the rhythms of nature, on which they depended, followed those of the Sun, Moon, planets and stars. These unchanging cosmic patterns were guiding life on earth. They had observed that of all life forms, trees followed these influences most closely. They could build on that. If trees had not yet sprouted, while the Sun had been above the horizon long enough, they waited with their spring activities. Then the weather was not favourable enough."

The Moon hangs like a world clock in the night sky. You could say, 'Let's meet at the next full Moon'. Every night you can see her progress, the perfect interface that does not require a sophisticated clock. The Sun determines day and night, and in our regions, it also determines the seasons. Imagine an alien species that sees no light (neither day nor night) and does not perceive the seasons, but for some reason is very sensitive to the slight movement of tree trunks, listens to it like a heartbeat. From the tree rhythms, they could deduce the movement and rotation of the earth and the sun: a short cycle for the unit of a day, a long and slow cycle for the unit of a year."

How has collaborating with nature and science influenced the artistic process?

"Since the creation of Anaïs Berck in 2019, nature and science have been ingredients of the artistic process. For Tree Times, we worked with bioengineer and holistic energy worker Aelyn Van Diest, who can communicate with the tree field and helped us understand the trees' perspectives.

Data scientist Anne-Laure Buisson was also part of the team. The way she juggles large amounts of data and code ensured that the artistic work was also fuelled by solid algorithmic analysis, which in turn was presented to Aelyn as a bioengineer and also to the trees."

How can visitors experience the project for themselves?

"Visitors can meet the trees in the different nature reserves until 5 November 2025; Grenspark Kalmthoutse Heide (on walking route Duin), the Liereman (in Korhaan) and National Park Bosland (next to the forest museum Pijnven). Each tree has a sign with a phone number with which you can request an excerpt from the diary.

In the various visitor centres and on the wall of the Forest Museum, you will find a copy of the artistic map, which can also be bought as artwork on paper at the respective counters. The telephone number for the diaries and the QR code that gives insight into the data are provided on the map."

On 2 November at 1.30pm, An will give a guided tour of Grenspark Kalmthoutse Heide. The walk will depart from De Vroente, Duurzaam Educatiepunt. Please book in advance via anais@anaisberck.be. The walk will last until around 4pm.