The Swiss Federal Institute for Forest Snow and Landscape Research WSL

Density matters

At the upper and northern forest limits, trees are particularly sensitive to temperature fluctuations. This is most evident in summer, when latewood is formed. Because of this, latewood from such trees is a reliable archive of summer temperatures.

Using X-ray densitometry, we measure the latewood density of thin wood slices.

We measure the grey values of x-rayed wood samples and convert them into tree-ring density curves. High maxima (black dots in the picture), i.e., years with dense latewood, indicate high summer temperatures.