Estimating a Trees Age Without Cutting the Tree

The most accurate way foresters determine the age of a tree is by counting the growth rings of a severed tree stump or by taking a core sample using an increment borer. However, it is not always appropriate or practical to use these invasive methods to age a tree. There is a noninvasive way to estimate tree age in common trees where they are grown in a forest environment. Growth Depends on Species Trees have different growth rates, depending on their species. A red maple  with a 10-inch diameter and competing with other forest-grown trees can easily be 45 years old while a neighboring red oak with the same diameter would only be approximately 40 years old. Trees, by species, are genetically coded to grow at about the same rate under similar conditions. A formula was previously developed and used by the International Society of Arboriculture (ISA)  to predict and determine a forestland  trees age. Running the calculations and comparing them to a species growth factor is regionally and species-specific, so these should be considered very rough calculations and can vary by region and site index. The ISA says that tree growth rates are affected tremendously by conditions such as water availability, climate, soil conditions, root stress, competition for light, and overall plant vigor. Further, the  growth rates of species within genera can vary significantly. So, only use this data as a very rough estimate of a trees age. Estimating a Trees Age by Species Begin by determining the tree species and taking a diameter measurement (or convert circumference to a diameter 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 a calculation to determine the tree diameter: Diameter Circumference divided by 3.14 (pi). Then calculate the age of a tree by multiplying the trees diameter by its growth factor as determined by species (see list below). Here is the formula:  Diameter X Growth Factor Approximate Tree Age. Lets use a red maple to calculate age. A red maples growth factor has been determined to be 4.5 and you have determined that its diameter is 10 inches: 10 inch diameter X 4.5 growth factor 45 years. Remember that the growth factors  provided are more accurate when taken from  forest grown trees with competition. Growth Factors by Tree Species Red Maple Species - 4.5 Growth Factor X diameterSilver Maple Species - 3.0 Growth Factor X diameterSugar Maple Species - 5.0 Growth Factor X diameterRiver Birch Species - 3.5 Growth Factor X diameterWhite Birch Species - 5.0 Growth Factor X diameterShagbark Hickory Species - 7.5 Growth Factor X diameterGreen Ash Species - 4.0 Growth Factor X diameterBlack Walnut Species - 4.5 Growth Factor X diameterBlack Cherry Species - 5.0 Growth Factor X diameterRed Oak Species - 4.0 Growth Factor X diameterWhite Oak Species - 5.0 Growth Factor X diameterPin Oak Species - 3.0 Growth Factor X diameterBasswood Species - 3.0 Growth Factor X diameterAmerican Elm Species - 4.0 Growth Factor X diameterIronwood Species - 7.0 Growth Factor X diameterCottonwood Species - 2.0 Growth Factor X diameterRedbud Species - 7.0 Growth FactorDogwood Species - 7.0 Growth Factor X diameterAspen Species - 2.0 Growth Factor X diameter Considerations for Aging Street and Landscape Trees Because trees in a landscape or park are often pampered, protected, and sometimes older than forest-grown trees, it is more of an art to aging these trees without significant error. There are foresters and arborists with enough tree core and stump evaluations under their belts who can age a tree with a degree of accuracy. Its important to keep in mind that it is still impossible to do anything but estimate a tree age under these conditions. For younger street and landscape trees, pick a genus or species from above and reduce the Growth Rate Factor by half. For old to ancient trees, significantly increase the Growth Rate Factor. Sources and Further Information Fien, Erin K. P., et al. Drivers of Individual Tree Growth and Mortality in an Uneven-Aged, Mixed-Species Conifer Forest. Forest Ecology and Management 449 (2019): 117446. Print.Lhotka, John M., and Edward F. Loewenstein. An Individual-Tree Diameter Growth Model for Managed Uneven-Aged Oak-Shortleaf Pine Stands in the Ozark Highlands of Missouri, USA. Forest Ecology and Management 261.3 (2011): 770–78. Print.Lukaszkiewicz, Jan, and Marek Kosmala. Determining the Age of Streetside Trees with Diameter at Breast Height-Based Multifactorial Model. Arboriculture and Urban Forestry 34.3 (2008): 137–43. Print.Pothier, David. Analysing the Growth Dynamics of Mixed Stands Composed of Balsam Fir and Broadleaved Species of Various Shade Tolerances. Forest Ecology and Management 444 (2019): 21–29. Print.