Since 26 May, a tree on the Wageningen University & Research campus has been active on Twitter. By posting updates on @TreeWatchWur, this thirty-year old poplar keeps its followers informed about its sap flow and secondary growth.
But why are we interested in this information?
Trees are a vital aspect of our climate. Most importantly, they absorb the greenhouse gas CO2 to promote their own growth and this CO2 remains stored in their wood. Especially a mixed forest partly made up of younger trees is capable of absorbing and storing large amounts of CO2. Trees also protect the soil against heavy rainfall, which promotes water retention and prevents soil erosion.
Climate change will bring extreme weather conditions such as droughts, heat, unexpected frost and flooding to Europe. According to Wageningen University & Research tree biologist Ute Sass-Klaassen, ‘we need to assess what this means for the growth and vitality of our trees. If a tree does not get sufficient water as a result of prolonged drought, for example, the tree will go into stress. This hampers its CO2 absorption and, thus, its growth. This growth retardation leaves marks in the wood of the tree. In this way, wood functions as an archive in which the experience of stress has been stored in the annual growth rings of the tree. We want to find the key which can unlock the information contained in these annual growth rings.’
Annual growth rings
Annual growth rings are the broad and thin lines visible on tree stumps. These rings are shaped by environmental factors throughout the year and can be seen as a type of weather archive. If the conditions are right, the tree will grow quickly and create large cells, while in poor conditions the tree will produce smaller cells. This gives each annual growth ring its own specific pattern.
For example, the size of the vessel elements shows whether the trunk of a tree has stood in water. While conducting research on oak trees along the IJssel river in Deventer researchers from Wageningen University & Research discovered that if, during the start of the growing season, an oak trunk stands in water, many smaller vessel elements are formed. However, this only occurred in the part of the trunk that was covered by water. In the higher trunk segments that were not in the water, the vessel elements were normal in size.
The secret lives of trees
Several trees across Western Europe have been fitted with measuring equipment to track the precise formation of wood structure in extreme weather conditions such as drought. This continuously measures the speed at which a tree transports water and how the diameter of the trunk of the tree changes. And just how does a tree transport water to its highest branches? That's explained in this video which Sass-Klaassen also shows to students.
The unique thing about this research is that the trees fitted with the measuring equipment tweet about their data. The tree on Wageningen University & Research campus tweeted on a bright and sunny 5 June: ‘Today I have grown 0.082 millimetres, transported 124.9 litres of water at a maximum sap flow of 9.8 litres per hour.’
Each tree also measures humidity, temperature and soil moisture levels. According to Sass-Klaassen, ‘the first results indicate that tree growth is more dynamic than we had initially thought.’ By tweeting the results in real time, the broader public gets given a glimpse into the inner life of trees. And during the day there's a lot more going on than you think!
Researchers can use the real-time information from the trees to develop models which help to discover how trees reacted to their environment in the past when they were under stress. ‘We can use this knowledge to design the forests of the future. It will help us to select the species and varieties needed to keep European forests resilient, so that they can continue to perform and strengthen their important function for climate control and as a source of wood and other products. This is why it is essential that funding is provided for this type of fundamental research for the preservation of our forests.’
The twittering tree research project was initially launched by the European research network Studying Tree Responses to extreme Events: a SynthesiS or STReESS, headed by Sass-Klaassen. 350 researchers from 37 countries, representing different disciplines including ecophysiologists, tree geneticists, forest ecologists and dendrochronologists, developed a concept and vision for discovering the secret lives of trees. Watch this video to see STReESS activities and the added value of interdisciplinary networking.