To save forests, researchers are hooking trees up to Twitter

Huge amounts of revealing data can be collected from sensors attached to trees.

Tim Rademacher, Harvard Kennedy School; Grace Field, University of Cambridge, and Kathy Steppe, Ghent University

In July 2018, a century-old red oak went live on Twitter. The account @awitnesstree, tweeting from the Harvard Forest in Petersham, Massachusetts, introduces itself in its bio:

Witnessing life as a tree in a changing environment for more than a century. Views are my own – sort of (data translated by scientists and communicators at HF).

Every few days, the tree updates its 9,118 followers. On February 24 2020 it posted: “The last 2 days were extremely hot for February. When is this heatwave going to end?”

The day before, it had complained even more:

Now, after a hiatus due to COVID-related challenges, the Witness Tree is coming back online.

The tree’s messages are based on data from a suite of sensors on and around its trunk, using a real-time approach to tree monitoring pioneered by Witness Tree’s inspiration and sister project Led by Ghent University, set up its first tweeting tree in 2016, and currently monitors sensor data from 21 trees across Belgium, Germany, India, the Netherlands and the UK.

The sensors fitted to Harvard’s Witness Tree include a ribbon embedded in its trunk to track water flow, a spring-loaded pin pushing against its bark to monitor shrinkage and swelling and a camera to capture leaf growth. Continuous data streams from these sensors tell us how the tree is affected by changes in its immediate environment. This technology is still in its infancy, but it shows exceptional promise.

Real-time sensors monitor the Witness Tree’s wellbeing.

By analysing data from Witness Tree and, we have already learned that drought can cause a tree’s stomata – the openings on the underside of its leaves – to close. The closed stomata block water intake, disrupting tree growth. More frequent droughts may therefore lead to less carbon uptake by trees and forests.

Harvard Forest’s Witness Tree.

Forthcoming studies even indicate that individual trees respond differently to the same heat waves, and that water transport in trees can react instantly to the presence of a solar eclipse. With the sun obscured by the moon, stomata close as they would do at night, immediately reducing water intake.

As we continue to assess incoming data from Witness Tree and, we will surely learn even more about how trees affect – and are affected by – their surroundings.

Science communication

The red oak at Harvard Forest, along with its Asian and European cousins at, is first and foremost a rich source of scientific data. But at the same time that data, when converted to tweets by custom-built algorithms, turns the Witness Tree into a platform for science communication research.

Behind the scenes, a computer program analyses the incoming numbers from Witness Tree’s sensors: cross-checking against pre-programmed thresholds for normal activity, looking for abrupt changes and compiling summaries.

For each key data feature, including daily water use, sap flow dynamics, stem shrinkage and trunk growth, the researchers at Harvard Forest have provided the program with several different prewritten message templates. The program chooses one of these templates, inserts the relevant data, and posts the completed message on Twitter as if in the tree’s own voice.

Because the messages are chosen from templates at random, they can be used as a testing ground to study how the public prefers to engage with different topics and writing styles.

Preliminary results suggest, somewhat surprisingly, that the Witness Tree’s followers engage equally with data-driven and narrative-based tweets. The addition of multimedia – through images, videos or data visualisation – generates more responses, likes and retweets. Any posts that directly concern climate change seem to attract the most attention.

The future

To gain access to even more data, both the Witness Tree project and are expanding. The single Witness Tree will soon become part of a forest network spread over urban, suburban and rural areas to study how trees function in different environments.

Future witness trees with fine particulate matter sensors sensitive to poor air quality could help grow awareness about environmental stress factors faced by humans and trees alike.

New trees monitored by will measure carbon lost due to tree respiration, paving the way for more accurate carbon accounting. By cementing our understanding of how trees contribute to the carbon cycle, we will be in a better position to reduce carbon output globally.

Long-term, Witness Tree and aim to work together to build a vast, international network of tweeting trees: in other words, an internet of trees. The data from this “internet” will provide invaluable insights into the wellbeing of our forest ecosystems – from detecting early signs of drought and tracking the impact of pests and pathogens to forecasting sap flow for maple syrup production.

The trees currently monitored by, spread across Europe and Asia.

As we have learned more about how trees interact with the ecosystems that they visually define, trees have often been represented as social creatures in recent research and popular writing. In a way, Witness Tree and play into this idea by giving their trees a human-like voice. They use personification as a tool to communicate effectively with a wide audience.

But it would be counterproductive to take this metaphor too seriously, because each tree’s voice is in fact a fiction fed by automated messages. Really, it’s the data talking – and the story that data tells is the brutally honest reality of environmental change.The Conversation

Tim Rademacher, Postdoctoral Research Fellow, Harvard Kennedy School; Grace Field, PhD Candidate in History and Philosophy of Science, University of Cambridge, and Kathy Steppe, Professor of Applied Plant Ecophysiology, Ghent University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Source: To save forests, researchers are hooking trees up to Twitter

Why trees grow at night

By Swiss Federal Institute for Forest, Snow and Landscape Research WSL
Trees form new cells by using the carbohydrates they produce through photosynthesis. However, it is not primarily the availability of carbohydrates that limits growth, but the water tension in the tree, the so-called water potential, as this study recently published in the journal New Phytologist shows.

The international research team led by Roman Zweifel at the Swiss Federal Institute for Forest, Snow and Landscape Research WSL has come to the surprising conclusion that trees grow primarily at night, and that this trend is largely explained by the level of air dryness. In the world’s first comprehensive study of radial stem growth with an hourly data resolution, the scientists analyzed data recorded over up to eight years on 170 trees of seven common species located at 50 sites all over Switzerland (> 60 Mio data points). Researchers from ETH Zurich and other research institutions in Switzerland and Europe were involved in the study. The sites investigated are part of TreeNet, a network in which stem radius changes of trees have been measured continuously using high-precision point dendrometers in parallel with information about the dryness of air (vapor pressure deficit, VPD) and soil (soil water potential) in Swiss forests since 2011.

The data show that the probability of tree growth varies significantly over the 24 hours of a day: stems shrink under the effect of water stress and expand in a range of 1-200 µm per day, and these fluctuations are superimposed on growth rates of 1-5 µm per hour.

Air humidity is key to tree growth

The research team concluded that VPD plays a key role as it allows for growth mainly at nighttime. In their study, during day time, high VPD severely limited radial stem growth and allowed only little growth, except in the early morning. “The biggest surprise to us was that trees grew even under moderately dry soil conditions when the air was humid enough. Conversely, growth remained very low when the soil was moist but the air was dry,” recalls Roman Zweifel, lead author at WSL. The reason for this is the limited water transport capacity of the trees: as soon as the air becomes drier, trees temporarily lose more water through transpiration than they absorb through their roots. The entire tree comes under tension, its water potential decreases, and growth stops regardless of the availability of carbohydrates.

Source: Why trees grow at night –, 2021-06-21

Plants bounce light to forest floor

Recent research has shown that plants help themselves grow by releasing volatile organic compounds. These chemicals form a mist of aerosols above the vegetation that blocks some of the direct light but enhances diffuse light. This boosts the solar radiation reaching the forest understory and increases growth.

Alexandru Rap from the University of Leeds, UK, and colleagues assessed the impact of plant volatiles on primary productivity by using atmospheric and vegetation models along with measurements of aerosols and plant productivity. Their findings, published in Nature Geoscience, show that globally plant volatiles boost vegetation productivity by around 1.23 Pg of carbon per year — equivalent to around 10% of the world’s fossil fuel carbon emissions.

“Amazingly we found that by emitting volatile gases, forests are altering the Earth’s atmosphere in a way which benefits the forests themselves,” says Rap. “While emitting volatile gases costs a great deal of energy, we found that the forests get back more than twice as much benefit through the effect the increased diffuse light has on their photosynthesis.”

Source: Plants bounce light to forest floor – Physics World, 2019-04-01

Hygroscopic aerosols linked to forest decline

Hygroscopic aerosols — particles in the air that attract water — could be causing forest decline around the world, according to experiments performed in Germany. Researchers believe that aerosol accumulation on trees enables thin bridges of liquid to form between the leaf interior and the leaf surface, causing the plants to dry out much more rapidly.

“In the atmosphere, aerosols act as cloud condensation nuclei,” says Juergen Burkhardt of the University of Bonn, Germany. “Deposited aerosols on leaf surfaces act almost the same way but attract water from inside the plant.”

Plants have developed sophisticated mechanisms for taking up carbon dioxide from the air for photosynthesis without losing too much water but, as the scientists note, it’s a delicate balance. And one that appears to be upset by rising levels of airborne particles.

“Global aerosol concentrations have roughly doubled compared with natural conditions, and the concentration increase over the continents is even higher,” says Burkhardt. “Our results show that aerosols deposited on leaves interfere with this delicate balance, pointing to a direct mechanism by which air pollution can reduce the drought tolerance of plants.”

Burkhardt and colleagues grew three species of tree — Scots pine, silver fir and common oak — for two years in two greenhouses, one ventilated with ambient air and the other fed with air filtered to remove 99% of aerosols. Seedlings grown under filtered conditions had superior drought tolerance to those raised in ambient air, the team found.

Source: Hygroscopic aerosols linked to forest decline – Brinkwire, 2018-09-25

Forests pull off a useful light trick

By Alan Duffy
Volatile gases emitted by trees scatter light to increase its availability to leaves.

That “pine-smell” you enjoy during a walk in the woods doesn’t just lighten your mood. It lights the entire forest itself.

Research published in the journal Nature Geoscience Letters, and led by Alexandru Rap of the University of Leeds in the UK, has found that the “smell” of a forest, caused by vast quantities of biogenic volatile organic compounds (BVOCs), increases the scattering of direct sunlight and allows it to reach the wider plant-canopy.

Illuminating more of the canopy leads to increased overall growth, more than offsetting the substantial cost in creating the volatiles to the plants, that captures an additional 1.23 billion tonnes of carbon each year.

The impact of these BVOCs was estimated in a simulation framework that included a global aerosol model to track their release across different habitats. It also employed a radiation model that changed the resultant sunlight, and a land surface scheme to model the resulting growth. These models have previously been used to estimate the impact of mass burn-offs in the Amazon region.

The modelling allowed researchers to explore the relatively uncertain range of global BVOCs production, as well as their changing impact on plant response – with some regions actually suffering a small decrease in growth.

The greatest impacts were in South America and central Africa, where direct sunlight scattered into an additional 10 watts of diffuse lighting across each square metre. This drove growth which sequestered an additional 0.2 grams of carbon per day per square metre. Taken globally, the growth more than compensated for the decline in certain regions.

Source: Forests pull off a useful light trick – Cosmos, 2018-08-21