CT scans for ancient Bristlecone Pine trees: unravelling the temperatures of the past from the gnarly and twisted trees

Ancient Bristlecone pine trees can live for several millennia and hold invaluable climate information. Their annual rings were used to develop millennium-length records of the Holocene climate. Maximum latewood density (MXD), which is the highest wood density value in the latewood of a tree ring, has been shown to closely follow summer temperature in different conifer species, but not yet in Bristlecone pine.

An international team of researchers from the University of Liège, Ghent University, the University of Arizona, and the Belgian Climate Centre has developed a new method to study the temperature signal of bristlecone pine trees. Unlike other trees, bristlecone pines are very difficult to measure due to their extremely slow, twisted, and gnarled growth.

The team used a tailored Computed Tomography (CT) toolchain to scan not people, but pieces of wood in order to measure properties on the tree rinsg. These pieces of wood, about the size and shape of a pencil, are extracted from the tree with a hollow drill without damaging the tree. The CT technique that allows us to 3D scan through the tissue of a tree ring and to map MXD variations.

Using this new technique, they are able to reconstruct warm-season temperature for the American Southwest back to 1625 CE. With these findings, the team is confident that a full-length reconstruction (back to 2575 BCE!) can yield the longest annually resolved temperature reconstruction for this continent.