(by Anita Zolles, BFW)

Zooming in on our dendrometer data! Did you know that tree circumference can change from one hour to the next? Aaaaaand… are they only increasing, or can tree trunk sizes also decrease? Actually both, as we can see in the three graphs that show the variation of tree circumference for a beech tree.

In the left picture you can see an overview for the year 2020. The winter growth break at the beginning and end of the year is obvious, where not much is happening (flat line). Zooming in on the 6.-10. of July in the middle plot, we see the circumference variation during few summer days. Finally, the plot on the right shows variation on one single day. During the daytime circumference typically “shrinks”, this is caused by depression within the stem (due to sap flow*).

* “Sap flow in a tree refers to the movement of sap, a nutrient-rich liquid, through the xylem tissue of the tree. The xylem tissue is responsible for conducting water and minerals from the roots of the tree up to the leaves and other parts of the tree.” (Answer provided by ChatGPT)