Section 6.1: Dendrochronology Data

Outcomes

Students will:

  • Understand what data is obtained from tree cores and how dendrochronologists collect this data.

Key Terms

Ring Width Index

See content or Module Glossary for definition

What Data Does Dendrochronology Obtain?

The word dendrochronology is derived from Greek roots. Dendro comes from dendron which means tree. Chrono means time and logy comes from logos which means the science of. More specifically, dendrochronology is the scientific method for dating tree rings and gaining information about the environments they live in based on the tree’s growth rate. See Figure 1 for an example of how tree rings can be used in correlation with technological milestones.

Tree rings grow annually at a varying rate, which causes differently sized tree rings (for more information, see Module 1). This rate is affected by a number of factors including: temperature, access to water, nutrients, etc. By measuring the size of the tree rings and how they change as the tree ages, dendrochronologists can understand the history of the environmental conditions around the tree.

The initial information gained from a dendrochronological study is the size of each tree ring and the total number of tree rings. By knowing the date that the tree was cored, dendrochronologists are able to count the tree rings back in time to the pith, marking the year the tree was planted. This tells dendrochronologists the age of the tree.

Due to the way trees grow in size, the information in the tree ring widths needs to be standardized before it can be used. Neglecting all environmental factors, an ideal tree will grow by the same volume of wood each year. However, adding the same volume of wood to the outside of a continually growing tree will produce smaller and smaller rings. To see that this is true, we encourage you to complete the Shrinking Tree Rings lesson.

Tree Rings & Technology.jpg
Figure 1 shows a tree trunk timeline with some major technological milestones. Image by Petar Milosevic.

Shrinking Tree Rings Lesson

Take various measurements as they relate to tree rings and inquire into what impacts them. Lessons can be downloaded and adapted from here: https://bit.ly/3DdJggV

Therefore, standardizing the tree ring sizes accounts for the natural decrease in tree ring size. By standardizing these measurements, dendrochronologists can then compare how big the tree ring is to how big it should be if the tree grew under ideal conditions. A tree's ring width index (RWI) tells the dendrochronologist which rings were above or below the tree’s average growth (Figure 2), indicating if the tree’s environmental conditions were suitable or not.

Figure 2 shows the natural decrease in tree ring width, as well as the inverse exponential curve used to standardize this decrease. Image by Taxelson.
Figure 2 shows the natural decrease in tree ring width, as well as the inverse exponential curve used to standardize this decrease. Image by Taxelson.

How is the MAD Lab Data Collected?

When the MAD Lab collects the samples from the CLS, they use the following process to collect information.

  1. Tree core samples are collected and sent to the MAD Lab (look at Module 4 to see how­).

  2. The tree core sample labels are transferred to the sample holder (the plastic holder shown in Figure 3).

  3. The tree core samples are then carefully removed from the straw sample holders.

    • The researcher makes sure broken pieces stay in the same order.

  4. The sample’s grains are aligned perpendicular to the sample holder* and then super glue is applied around the edges of the sample and the sample holder.

    • *This allows the researchers to see the annual ring as clearly as possible.

  5. Once the super glue has dried completely, the samples must be sanded down with progressively finer sandpaper until all of the rings are visible (shown in Figure 4).

Figure 3 shows an example of a finished set of samples at MAD Lab.
Figure 3 shows an example of a finished set of samples at MAD Lab.
Figure 4 shows a MAD Lab student researcher sanding down TREE cores to better expose the annual rings.
Figure 4 shows a MAD Lab student researcher sanding down TREE cores to better expose the annual rings.

6. Each tree core sample is then measured. As shown in Figure 5, using a stage system, a microscope, and a measuring program, researchers measure the individual tree ring widths. Once all of the rings are measured, researchers can count back and date the age of the sample.

  • The sample stage used in the Figure is a velmex positioning stage. A velmex machine is used to increase the accuracy of the measurement, while the camera is used to take images of the rings. The stage below moves the board from side-to-side and is accurate to one micrometer.

Figure 5 shows a MAD Lab student researcher measuring the position of each tree ring on TRE sample cores.
Figure 5 shows a MAD Lab student researcher measuring the position of each tree ring on TRE sample cores.
TREE Video on the method of dendrochronology: http://bit.ly/TREE_MADLab

Additional Resources for Section 6.1

  • The Mistik Askîwin Dendrochronology Laboratory Website: http://www.madlabsk.ca/
    MAD Lab's home webpage where you will find lots of information on their crew, the types of projects they explore, examples of the various equipment they have, different reports and theses that have come out of the work they have done, and so much more!