Reading a Trees Rings (Or Visualising Past Weather Events)

This Instructable explains how to read the rings that you can see within the cross-section of a tree (tree stumps or cross section slices). This allows various information to be determined including the age of trees, weather and climate in the past, significant events in the trees life and cross dating.

1. Tree stump or wood slice.
2. Notebook and pen.
3. Wet cloth (optional).
4. Sandpaper (optional).

This step explains how to find a suitable tree stump. Find a tree that has been recently cut down, that has a tree stump that is easy to see. It is important that there is a continuous flat surface from the centre of the tree stump to the edge of the tree stump.

If the surface of the tree stump is too rough or dirty to read, wipe it down with the damp cloth and/or sand it with the sandpaper. It is important to know what year the tree was cut down, in order to determine when it was a seedling

In this step we will determine the age of the tree and the year that it was born. We will determine the trees age by looking at its growth rings. Trees typically have two types of growth rings per year, a large wide ring from spring and early summer and a narrow ring from late summer and autumn at the end of the growing season. For this step we will consider that both these rings are one ring that represents a trees yearly growth.

1. Locate the centre ring of the tree, this is the ring formed by the first year of the trees growth, when the tree was a young sapling.
2. Count the number of rings present in the cross section. If the distance between the rings is not constant in the cross section, count the rings in the direction that has the largest spacing between the rings as this will make them easier to count. In my case the tree was 20 years old, as shown by its 20 growth rings.
3. The year when the tree was a seedling can be determined by subtracting the age of the tree from the year that it was cut down (Year planted = Year chopped down - age of the tree). In my case the tree was planted in year 2005 as year planted = 2025 - 20 = 2005.

During years with heavy rainfall and favourable growing conditions trees will have large thick growth rings whereas during years with little rainfall and unfavourable growing conditions they will have thin narrow growth rings. The succession of growth rings can be examined in order to determine periods of good or bad weather. However it is also important to remember that a trees growth can be influenced by the local microclimate i.e. property developments and the growth of other nearby trees.

Tree rings can show significant events that happened during a trees life, for example forest fires or insect attacks. Forrest fires can show up a trees growth ring record as a fire scar (a black burnt mark at the edge of the tree ring), whereas an insect attack can show up as scars or unusually narrow growth rings in the trees cross section.

Cross dating is when the growth rings in a trees cross section, are linked to the growth rings in another nearby trees growth rings. This is done by comparing the growth rings in each sample and linking them where the growth pattern overlaps. This can help to verify and improve the accuracy of the data, and to provide further insights into the past that the cross section did not provide.