Inside:  Determining tree age can be done in a few ways.  One is simple enough to do as a science activity with kids.  Tree aging can provide a wealth of information.  Examining tree rings can not only age a tree but also provide a lot of interesting historical and climate information. *Amazon affiliate links are found below.  If you click I may make some coffee money at no cost to you.

To determine tree age, pro skills are not necessarily required.  If you’d like to have your kids or students engage in a fun, hands-on activity, estimating tree age requires few materials.  But why would you bother?  What is worth knowing about how old a tree really is? And how can you measure the age of a tree anyway?

The Importance of Trees

If you want to find reasons trees are ecologically important read this post.  Here I outline 10 reasons trees are important to a healthy planet but I’m sure you could come up with so many more.  Dendrochronology is the study of data collected from tree ring growth.  Counting tree rings is one of the ways to determine tree age.

Tree Age

Tree age is important information to scientists and horticulturists.  For the forestry industry it can:

• determine the average age of a stand of trees
• provide information on how quickly trees are growing
• show the relative quality of a forest site through the average height of the dominant tree species at a specific age
• predict the future monetary value of the site when harvesting trees
• allow foresters to predict the productivity of the land for trees and wildlife

For landowners and horticulturists, tree aging information can determine:

• the benefits of a tree ecologically and economically,
• what trees to plant in a yard
• and where.

Determine Tree Age by Counting Rings

Tree rings provide a snapshot of the environmental pressures experienced by the tree in its lifetime.  A tree’s rings can not only tell us the age of the tree.  Other cool stuff you can learn from tree rings:

• climate changes – wide rings mean there was plenty of sunlight and rainfall while thinner rings indicate a cool, dry year
• floods
• insect damage
• high wind damage
• fires

The State of Canada’s Forests: Annual Report 2017, Natural Resources Canada, 2017. Reproduced with permission from Natural Resources Canada, Canadian Forest Service, 2018.

Counting tree rings is possible because many trees grow new tissue each year.   Light colored and wider ring-tissue grows in the spring and early summer while the tree grows dark narrower tissue in the late summer and fall because of fewer nutrients and less sunlight.  A dark colored ring and the neighboring light colored ring represent one year of tree growth.  Counting these rings is an effective way to determine tree age.

Growth Rings in Trees

• This method is great for dead trees.
• Living trees can be dated using an increment borer. To work the borer needs to be longer than the radius of the tree. Like taking an ice core sample, this borer takes a core sample to the pith in the middle of the tree trunk. Tree rings can be counted in this core sample and the tree is not permanently damaged.  The hole must be sealed with something like wax to prevent infection.

Determine tree age using an increment borer. source

Determine Tree Age Using a Tape Measure (ya, you read that right!)

You can estimate the age of a tree without counting rings. All you need to know is the species of tree and the tree’s circumference.  A chart of trees and their growth factors is required as well.  Scientists understand that trees grow at different rates.  As well, they know that different trees respond differently to environmental factors.  Knowing this, researchers have been able to figure out a growth factor for each tree species.  I’ve provided a chart of growth factors below.  This method can be used in a great activity with middle school and high school age kids.

1. Determine the correct species of tree.  Check out an Amazon offering below to identify North American trees near you.
2. Wrap a tape measure around the tree trunk about 4½ feet above the ground, measuring the circumference of the trunk in inches.
3. Multiply the tree’s circumference by 3.14 to determine the tree’s diameter in inches.
4. In the chart below, find your tree’s growth factor and multiply it by the tree’s diameter.

Sources: The Living Urn & Minnesota Project Learning Tree

Estimating age of a sugar maple:

1. circumference = 5 feet 4 inches
2. its diameter = 64 inches / 3.14 = 20.4 inches
3. 5.0 (growth factor)x 20.4 inches (diameter) = 102

This sugar maple is about 102 years old.

Tree Age and the Benefit of Trees

National Tree Benefit Calculator is an on-line tool giving students an understanding of the environmental and economic value trees provide the environment and landowner on an annual basis.  Simply input your location by postal code or zip code, the tree species and and size.  Specifically for urban trees, this calculator assesses the economic value of a particular tree in terms of:

• how much storm water it intercepts
• how much it raises your property value
• energy savings it influences
• improvements it provides in air quality
• carbon dioxide reduction

So, why not head out to your favorite arboretum and try to estimate the age of some of their trees.  A tape measure, tree field guide and a calculator are all you’d need.  If you’re fortunate to live in a well-treed neighborhood you could check out the age of some of the neighborhood trees.  This activity would be great for home school or for classroom teachers (hopefully your school has some trees or a field trip might be in order).  Learn about trees, have your students brush up on measurement skills and tree identification.  Don’t forget to log on to the National Tree Benefit Calculator to discuss the benefits of the trees in your neighborhood.