Determining the Age of a Tree Using Circumference

I love this science activity.  It is great for two reasons.  1.  The kids have been doing geometry in math and are already studying circumference and diameter of circles.  2.  They really begin to understand that studying trees is a science and that Math has a practical purpose in life.  So I am sharing this for anyone who needs a great Common Core Math lesson on Circumference, Diameter, and its relationship to Pi or for anyone who just wants to show their kids the science of determining the age of a tree without harming one.

Supplies

You will need a few things to start:

1.  calculators (or not, if you want them to practice mutiplying and dividing huge amounts of decimals)

2.  long pieces of string or yarn

3.  rulers or yardsticks

4.  growth factor charts for different species of trees.  The best one I have found was here at the Missouri Dept. of Conservation.

My "fake" trees

5.  Fake trees (mine consist of wrapping cylindrical shaped objects with brown paper) and/or real trees.

6.  An engaging video that shows them what this is like in the field.  I use this one with Steve Stillett measuring Redwood trees.

7.  Blank worksheet that includes the directions, formulas, and a chart to record their data

Calculating the Age of a Tree Worksheet

The students have "fake" tree options in the classroom and a few real tree options outside.  I have them work in partners because using the string and laying it onto rulers or yardsticks sometimes requires four hands. Plus, the conversations about the math often create a few lightbulb moments for some kids.  Essentially, the formula is as follows:

Diameter x growth rate = tree age

They need to measure the circumference, divide that by 3.14 to get the diameter, then multiply by the growth rate on the chart based on what type of tree it is.

I find that students who did not really understand circumference and diameter beyond the formula, have a much better understanding of their relationship once this is done. They also really enjoy what they are doing.  Especially when I let them go outside and try it on real trees.  When they are done, they get glued into their interactive notebooks.

Let me know if you have any questions about the lesson, but if you spend any time on either of these subjects it is well worth the time and effort.