Tree Coring Basics

In order to successfully reconstruct the past climate of a region using tree rings a number of criteria must be satisfied:

1. trees sensitive to climate must be present;
2. a large number of samples must be available from each tree and the entire area;
3. tree ring samples must cross date within a site; and
4. tree ring samples need to show a strong correlation between sites.

Dendrochronology field work consists of multiple steps.First an area needs to be scouted to determine if a large enough and old enough sample can be collected. This includes observing the area using satellite images, traveling to the area to observe the trees, and collecting a few samples from the area to determine the age of the trees. If a site is deemed worthy then intensive sampling can commence. This entails sampling 60-70 trees with 2-6+ samples being extracted from each tree. Samples are extracted using an increment bore (Figure 5, top right).  The auger is fully twisted into the tree and then the extractor is inserted to break the core from the tree. The auger is then twisted out of the tree and the core is extracted (Figure 6, bottom right). Cores are stored in plastic straws until laboratory preparation.

When in the laboratory the tree rings are removed from their straws and mounted (Figure 7). Samples are then sanded with increasingly finer types of sand paper (Figure 8). This creates a polished look and allows for the rings to be more easily identified. Samples are then placed under a microscope where rings are counted, skeleton plots are made, and a master chronology is created (Figure 9, Figure 10).

Figure 7	Figure 8	Figure 9	Figure 10