How to Identify Tree Age

A cross sections of a tree is also known as a tree cookie.

While you may be aware that the number of rings inside a tree's trunk correlates to its age, determining the age of a living tree can be difficult. You can identify the age of a tree through examining a cross section, or cookie, of its trunk once it has been cut down, or by extracting a core sample using a tool known as an increment borer.

Things You'll Need

• Increment borer or cross section of the tree
• Hand lens or magnifying glass
• Paper and pen

Instructions

1. Obtain a cross section of the tree or use an increment borer to extract a core sample. To use an increment borer, assemble the borer according to the manufacturer's directions. Drill the borer into the tree until you reach the center of the tree. Slide the extractor into the borer and then pull it out, removing a piece of tree core using the extractor.

2. Set your piece of tree or tree core on a flat surface. Identify the pith, or center, of the tree cookie or the pith end of the piece of tree core.

3. Examine the tree and look at its rings. A tree adds a ring each year that it grows. Each ring radiating out from the center should have a lighter band from spring growth and a darker band from the fall growth. If necessary, use a magnifying glass or hand lens to view the rings.

4. Count the rings, starting with the first dark ring next to the pith and continuing until you reach the last ring. Do not count the pith at the center or the bark on the outside of the tree.

5. Add up the number of rings. This is the tree's age, in years.

Tips & Warnings

• Using an increment borer may be difficult depending on the tree's wood density, and it can be tricky to determine when you have reached the center of a tree. Regular practice is required in order to achieve consistent results.

• Select an increment borer that is appropriately sized for the tree. The borer should be at least 3/4 of the tree's diameter in length.

• Extracting even a small core sample can potentially introduce decay into the tree trunk and damage the tree.

References

• Ball State University: Electronic Field Trip: Lesson: Tree Rings
• Virginia Cooperative Extension: Measuring Site Index
• USDA Forest Service Northeastern Area: Urban Forestry Lab Exercise: How Old Is This Tree?

Resources

• University of Tennessee: The Ultimate Tree-Ring Web Pages: Increment Borers