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Polar shrubs as living archives |
8 August 2024 |
As soon as the fog has lifted on Monday evening, I almost run outside to take samples together with Floortje. I am leaving in a few days, and I am not sure yet how much time I will need for sampling, and whether there will be more fog or bear days. I will take wood samples of the polar willow (Salix polaris), to study its tree-rings. Tree-ring studies on polar shrubs is probably one of my favourite research methods, because I find it so wonderful and strange that something so small can contain so much data. On Wednesday, I finish the last sample together with Sanne and Floortje, who filmed the whole process, in the pouring rain. 
 This is more or less how tall a shrub grows on Svalbard. The twigs are not even half a centimetre thick. Unbelievable that you can still see tree rings in the wood, but you really can! I carefully dig out a shrub and take samples of the branches, roots and root collar (the transition between the root and branch system). This way, I hope to find the oldest part of the shrub with the most tree rings (the root collar), but also have samples of younger shoots that clearly show the rings of the past few years. The reason I need to see these is that the polar willows are sampled from an experimental site where we artificially supplied extra rain in 2022 and 2023. Now I would like to know how that has affected wood growth and wood characteristics.  A shrub, with Ny-Alesund in the background.  The wood samples will be taken to the DendroLab in Wageningen, where we will cut the samples into micrometre thin cross sections, and digitise those under the microscope. Then we measure the width of the tree rings and size of wood vessels. A large ring means a lot of wood growth that year, and hence more carbon sequestration. A small or even absent ring means that something limited wood growth that year. Large wood vessels means that the shrub can easily transport water from the soil, but also that it is more sensitive to damage due to drought or frost. By comparing the tree-rings over the years to annual weather data, we can understand which weather conditions affect growth positively or negatively. And that yields important clues about how this species will cope with a changing climate.  Microscope photo of a cross section of a Salix polaris branch. In the middle you can see the pith, surrounded by tree rings. The tree rings are indicated by a kind of darker line at the end, and large, white wood vessels at the beginning. You can see that the rings are sometimes partially missing. How many rings do you count? |
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