Every tree holds a hidden history within its trunk. Researchers at the University of Antwerp are studying these annual rings to better understand how trees grow and respond to changes in their environment, such as global warming.
Dendrochronology is the science of tree rings. Scientists have long used tree rings to determine the age of trees or to date old wood. This enables them to investigate historic buildings or reconstruct past climatic conditions. By comparing thousands of tree rings, researchers are building databases that allow them to look far back in time.
Wide rings and small scars
Each annual ring reflects a tree’s growth, explains Kobe Happaerts (Faculty of Science) of the Plants and Ecosystems (PLECO) research group. “A wide annual ring usually indicates good growing conditions, such as sufficient light, warmth and water. A narrow ring may mean that a tree experienced stress due to drought, shade or other factors. Did you know, by the way, that not all trees in the rainforest have distinct annual rings? That’s because they don’t have to adapt to seasons as we know them here.”
Happaerts mainly investigates how a growth ring develops in real time. He does this by using wood samples taken weekly from trees in the forest during the growing season. “We take a small block measuring about two millimetres by two centimetres from the trunks of the trees we’re monitoring,” he says. “Trees recover from this very well, although you do see a small scar on most species.”
Carbon in the tree
He then analyses these samples using a CT scanner. This produces a three-dimensional image of the wood. “Traditionally, wood research involves measuring circumference and examining thin slices of wood in 2D under a microscope,” says Happaerts. “With CT scans, we can view wood growth in 3D and instantly measure how much biomass and carbon the tree stores at each stage.”
Every tree carries a unique growth story. In a Italian forest, I came across a small tree just thirty centimetres tall, which turned out to be a hundred years old.
Happaerts links the data from these CT scans to data from the European monitoring network Integrated Carbon Observation System (ICOS), which tracks how greenhouse gases such as CO2 are being absorbed or emitted by our ecosystems. In this way, he investigates how carbon dynamics relate to wood growth in deciduous trees such as the beech, about which less is known than about conifers.
‘The better we understand how trees respond to growth factors such as drought or heat, the better we can predict future forest developments and, if necessary, take corrective action,’ says Happaerts.
Thirty centimetres in a hundred years
According to Happaerts, we underestimate how complex tree growth is. “We sometimes know surprisingly little about certain fundamental processes behind wood formation,” he says. “How do the different wood cells of a tree species react throughout the year? What impact do heat, drought or other stress factors have on those reactions?”
According to Happaerts, every tree has its own growth story. “During a summer school in Italy, I came across a small tree just thirty centimetres tall. It had always stood in the shade of larger trees, and analysis revealed it was a hundred years old. Some of the annual rings consisted of barely a single cell. That perfectly illustrates just how profound environmental factors are for a tree.”
A tree as a witness to history
During the STROOM festival, researchers from the University of Antwerp will combine dendrochronology with music and heritage during the Double Bill: WALD x Memories of Trees concert. On the concert site stands a remarkable tree that has been there longer than the abbey itself.
Watch how researchers take a sample
During the festival, researchers will take a sample from the tree on site to examine the growth rings together with visitors and determine its age as accurately as possible. This way, you can discover live how scientists read hidden stories from wood.