Tree Ring Dating & Measuring a tree’s diameter Trees provide us with paper, lumber, plywood, pine pitch, dyes, turpentine and many other products. They also provide us with shade, beauty, oxygen, clean air and water, reduce soil erosion, and fruit. Trees are regarded as an important renewable natural resource but many take many years to grow and reach maturity. Their renewal requires careful planning. Once older trees have been harvested, new trees need to be planted in order for this resource to be renewable. Tree rings can be used to estimate a tree’s age as well as provide important ecological information. Each ring represents one year’s growth. Wide rings represent good growing conditions whereas narrow rings represent poor conditions. Tree rings are formed from the center outwards. The ring towards the center is the oldest and the ring closest to the bark layer is the youngest. Foresters use an instrument called an increment borer to determine the age of a tree. The increment borer is used to obtain a core sample that is approximately 1/8 inch in diameter. This is preferable to cutting down a tree and counting the annual rings in a transverse section. The following lab activity will give you a basic idea of the principle of tree ring dating by using simulated core samples – one sample is from tree (A) and another is from a Forest Ranger’s cabin (X). This exercise was adopted from Dendrochronology Tree Ring Dating Kit Cat. No. 52 by Lab Aids Inc, Ronkonkoma, NY 11779. How can you measure the diameter of a tree? A common method is to use a special measuring tape called diameter tape. This is calibrated tape where every 1 inch marked on the tape corresponds to 3.14 inches or Pi. If you use a regular cloth tape then you will need to divide the circumference measurement by Pi (3.14) to obtain the diameter. Procedure: Find some big trees on campus. 1) Determine breast height (dbh) for a given tree. This is about 4 ½ feet from the base. 2) Wrap the diameter tape around the tree at breast height. The reading from the diameter tape is the diameter of the tree at breast height. Make sure the tape is level and not twisted. The diameter measurement is read where the tape overlaps with the zero marker. 3) Record this information for five different trees. Usually trees become wider as they get older and older. The more girth a tree has, the older the tree. dbh Tree Species A. B. C. D. E. The Tree Aging Formula Begin by determining the tree species and taking a diameter measurement (or circumference measurement) using a tape measure at Diameter Breast Height or 4.5 feet above stump level. If you are using circumference, you will need to make this calculation to determine the tree diameter: Diameter = Circumference divided by 3.14 (pi) Then calculate the age of the tree by multiplying the tree's diameter by its growth factor (see below): Diameter X Growth Factor = Approximate Tree Age. Let's use the hickory above to calculate age. A shagbark hickory's growth factor has been determined to be 7.5 and its diameter is 10 inches: 10 inch diameter X 7.5 growth factor = 75 years. Growth Factors by Tree Species Red Maple Species - 4.5 Growth Factor X diameter Silver Maple Species - 3.0 Growth Factor X diameter Sugar Maple Species - 5.0 Growth Factor X diameter River Birch Species - 3.5 Growth Factor X diameter White Birch Species - 5.0 Growth Factor X diameter Shagbark Hickory Species - 7.5 Growth Factor X diameter Green Ash Species - 4.0 Growth Factor X diameter Black Walnut Species - 4.5 Growth Factor X diameter Black Cherry Species - 5.0 Growth Factor X diameter Red Oak Species - 4.0 Growth Factor X diameter White Oak Species - 5.0 Growth Factor X diameter Pin Oak Species - 3.0 Growth Factor X diameter Basswood Species - 3.0 Growth Factor X diameter American Elm Species - 4.0 Growth Factor X diameter Ironwood Species - 7.0 Growth Factor X diameter Cottonwood Species - 2.0 Growth Factor X diameter Redbud Species - 7.0 Growth Factor Dogwood Species - 7.0 Growth Factor X diameter Aspen Species - 2.0 Growth Factor X diameter http://files.dnr.state.mn.us/education_safety/education/plt/activity_sheets/howToUseADiameterTape.pdf http://forestry.about.com/od/silviculture/a/Estimating-A-Trees-Age.htm