Dendrochronology

Overview

Dendrochronology is the scientific study of trees growth rings. Much can be learned about a tree, the forest it’s in and also the regions historical climate by analysing growth rings. Students of any age find this process fascinating. The great thing about dendrochronology is that it can be quick afternoon activity or the basis for an entire unit of inquiry, problem solving and interdisciplinary connections.

Materials

  • Increment Bore (tree core sampler)
  • Tree Core Tray
  • Sand paper
  • Optional
  • Clinometer
  • Tree Diameter Tape (DBH Tape)
  • 10 meter tape
  • Tree ID book or local knowledge
  • Flagging tape or tree tags

Time

1 hour to multiple outings over a semester

Audience

Gr. 4-12Some Gr.4-7 students will need assistance boring a tree.

Procedure

Coring a Tree

It’s important that students understand how a tree grows prior to attempting a core extraction.If you take a core sample at chest height you may have just missed the first 20 years of tree growth! An attempt should be made to use the increment bore as close to the ground as possible without striking the ground each time it is rotated.

(ILLUSTRATION)

The bore should also be aimed at the centre of the tree as to not miss the heart wood. Getting the increment bore started requires some pressure and this can be challenging for younger students. In order to obtain a complete sample you only need to drill halfway through the tree.

(ILLUSTRATION)

Once you’ve reached this point insert the extractor bit completely into the bore. Turn the bore one half-turn counter clockwise and then back again. This helps the core release. With steady hands pull on extractor bit while the bore remains in the tree. The core sample should come out on the extractor bit. Be sure you have extracted the entire core sample.

(ILLUSTRATION)

Working with a Core Sample

The core is fragile. Care should be taken placing it in the core tray. Once dried you can sand the core and analyse the growth rings.

There is a lot of data and interesting information hidden in the rings. I suggest attaining the following:

  • Tree age
  • Significant grow phases and specific years
  • Low growth phases and years
  • Indication of an extreme event (forest fire, flood, tree damage)

Students should be challenged to find out what caused the years of significant growth and years of low growth. Historical weather information found on Environment Canada’s website is a great place to start searching for correlations. A field day collecting cores and counting them is often followed by a session in the computer lab.

Release Events

A release event in the forestry world refers to an event which results in tree suddenly gaining access to sunlight or new levels of moisture. An example of a release event would be clearing a section of forest in order to build a school. The trees that remain may experience a release event as they will suddenly gain more access to sunlight and competition for ground water and nutrients has been removed. This can result is a sudden expansion of the growth rings in subsequent years.

Fun Challenges

Consider challenging your students to identify when they suspect their school was built based only on information they can gather from tree core samples. You can apply this same challenge to subdivision, roads or any other disturbance of a natural forest.

Sampling trees along rivers can also reveal an interesting historical record of floods. Over saturated roots of river bank trees can stunt the growth and this evidence will result in a narrow growth ring. Can students find a correlation between narrow growth rings and flood years?

Problem solving and collaboration suddenly become important

Carbon Sequestering

Tree are excellent at storing carbon, also referred to as sequestering. Trees do this as they grow. Carbon is stored within the trees cells and oxygen is released to the atmosphere.

Did you know?

The oldest living tree (that we know of) in Yukon is a White Spruce nearly 700 years old! There may be older trees out there. Time for a field trip!

Assessment

Risk Management

  • Always set boundaries for your students that they can recognize and understand
  • Have students work in pairs or small groups
  • Visit the site prior to going with students
  • Establish a means of communicating to all students, such as a whistle, and a meeting place

Extensions

  • Forest Perfume
  • Paint Chips
  • Greet a Tree
  • Forest Ground Cover
  • Tree Identification