How to Determine the Age of a Tree
Have you always wondered about the age of the giant tree in your backyard? If you don't know the date the tree was planted, measure its circumference to estimate its age. While less accurate, a measurement estimate is the easiest method. If it’s an evergreen, count its whorls, or rows of branches. Broadleaf trees produce whorls irregularly, so counting them is only practical for evergreens. Counting the rings yields the most accurate estimate, but you shouldn’t cut down a healthy tree just to determine its age. Instead, to count a living tree's rings, take a core sample using an increment borer.
Estimating Age by Measuring the Trunk
Measure the tree’s circumference at breast height.Average breast height, which is a forestry measurement, is ft (1.4 m) from ground level. Wrap a fabric measuring tape around the trunk at this height, and note the tree’s circumference.
- If the ground is sloped, measure ft (1.4 m) from ground level on the uphill side, mark the spot, then do the same on the downhill side. The average breast height is the midpoint between the uphill and downhill measurements.
- For a trunk that forks at a height less than ft (1.4 m), measure the circumference just below the fork.
Find the trunk’s diameter and radius.To find the diameter, divide the circumference by pi, or approximately 3.14. Then find the radius by dividing the diameter by 2.
- For example, if the circumference is 154 in (390 cm), the diameter is approximately 49 in (120 cm), and the radius is about241⁄2 in (62 cm).
Subtract to 1 in (0.64 to 2.54 cm) to account for the bark.For tree species with thick bark, such as black oak, subtract 1 in (2.5 cm) from the radius measurement. Subtract in (0.64 cm) for species with thin bark, such as birch. If you’re not sure and just want a rough estimate, subtract in (1.3 cm) from the radius.
- Including the bark would add extra girth and throw off your measurements.
Use nearby felled trees to calculate an average ring width.Check around the tree in question for dead or felled trees of the same species. If you find one with visible rings, measure the radius and count the rings. Then divide the radius by the number of rings to find the average ring width.
- Suppose there’s a nearby stump with a radius of 25 in (64 cm), and you count 125 rings. The average ring width would be in (0.51 cm).
- Growth rates vary by tree species and environmental conditions. The living tree you’re measuring probably grew at a rate similar to a tree of the same species that grew nearby.
- You’ll plug your ring width measurement or, if there are no nearby stumps, an average growth rate into an equation to estimate the tree’s age.
- Even if you have the average ring width, you can also use the average growth rate to estimate the age, then compare the results of the 2 methods.
Look up the species’ average growth rate, if necessary.If you can’t find any nearby stumps or felled trees, search online for the average growth rate for the species of the tree you’re measuring. Including your location in your search terms could yield more accurate results.
- For example, oak, ash, beech, and sycamore trees grow about to in (1.3 to 1.9 cm) in circumference per year. If you don’t know the species, plug both in (1.3 cm) and in (1.9 cm) into your equation to guess an age rage.
- For a more accurate estimate, factor in the tree’s location. In open conditions, growth rates are usually greater, or to 1 in (1.9 to 2.5 cm) per year. Growth tends to be slower in urban locations and crowded forests.
- Be sure to check how the growth rate is calculated. Many sources base growth rates on how much the tree’s girth, or circumference, grows per year. However, you might find rates based on the average ring width of the radius.
Divide the radius by the average ring width.If you used a nearby stump to calculate the average ring width, divide the radius of the living tree in question by the average ring width.
- Say that, excluding the bark, your tree has a radius of about 24 in (60.96 cm). Using a nearby tree stump of the same species, you calculated an average ring width of 0.20 in (0.508 cm).
- Divide 24 (or 60.96) by 0.20 (or 0.508) to come up with an estimated age of 120 years.
Divide the circumference by the average annual growth rate.If you found the average annual growth rate based on girth, or circumference, divide your tree’s circumference by the growth rate.
- Suppose your tree’s circumference is 154 in (391.16 cm), and its growth rate is between 0.75 and 1 in (1.905 and 2.54 cm) per year. Divide 154 (or 391.16) by 0.75 (or 1.905), then divide 154 (or 391.16) by 1 (or 2.54). Your estimated age range would be between 154 and 205 years old.
Counting Branch Whorls
Count whorls to estimate the age of a conifer.Whorls are rows of branches that grow from the trunk at approximately the same height. Counting whorls is an option for conifers, or evergreen trees, but isn’t very useful for broadleaf trees, like oak or sycamore. This method isn't as accurate as counting the rings, but it's a way to estimate the tree's age without having to kill or injure it.
- Conifers produce whorls annually at regular intervals. Deciduous, or broadleaf trees, produce them irregularly, making it difficult to get an accurate count.
- It’s also easiest to count the whorls of a young conifer. You might not be able to see the top of a tall, mature conifer, and there would be more irregularities in its growth patterns.
Count the rows of branches growing at the same height.At the base of the tree, look for a row of branches that grow at the same level, a bare length of trunk, then another row of branches. These rows are the whorls; count them until you’ve reached the top of the tree.
- You might see single branches growing between whorls or 2 whorls spaced closely together. These are irregularities that might indicate an injury or unusual weather conditions that year, so don’t count them.
Include any stubs or knots at the bottom of the trunk.Check beneath the first row of branches for evidence of prior growth. Look for knots in the trunk and stubs where branches once grew, which you’ll count as additional whorls.
- For instance, suppose your tree has 8 recognizable whorls. Beneath the first row, you can see a few stubs that emerge from the trunk around the same level. There's also a row of 2 or 3 knots under the stubs. You’d count the stubs and knots as additional whorls, so your total count would be 10.
Add 2 to 4 years to account for seedling growth.The tree germinated and grew as a seedling for a few years before it started sprouting woody whorls. Add 2 to 4 to your whorl count to factor in this early growth.
- If your whorl count was 10, your final age estimate would be between 12 and 14 years.
Counting the Rings on a Stump
Examine the rings of an exposed stump.The number of rings on a stump indicates the number of years the tree lived. You’ll see rings of darker and lighter bands; 1 year of growth is composed of both a dark and light band. Since they’re easier to distinguish, count the dark bands to estimate the age.
- The rings can also tell you about the environmental conditions for a particular year. Thinner rings represent colder or dryer years, and thicker rings represent better growing conditions.
Sand the stump to see the rings more clearly.If the rings are hard to make out, start by sanding them with coarse, 60-grit sandpaper. Finish with a very fine sandpaper, such as 400-grit. Spraying the surface lightly with water can also make the rings easier to see.
- You might find that some rings are too close together to see clearly. If necessary, use a magnifying glass to get a better view.
Count the rings from the pith to the bark.Find the pith, or the small circle at the center of the concentric rings. Start counting from the first dark band around the pith. Continue counting until you’ve reached the bark. The last ring is pressed up against the bark and hard to see, so make sure to include it in your count.
- If you have trouble keeping track, try writing a number or making a mark every 10 rings with a pencil.
Counting Rings on a Core Sample
Take a core sample of a living tree using an increment borer.To accurately estimate the age of a living tree without killing it, use a borer to take a core sample. An increment borer is a T-shaped instrument composed of an augur, or a bit, and an extractor, which fits into the augur. The end of the T-shape is a handle, which you turn to drill in and out of the tree.
- The length of your increment borer should be at least 75% of the tree's diameter. You can find increment borers online and at forestry supply stores.
Drill into the trunk at breast height.Measure ft (1.4 m) up the trunk from ground level. Position the borer’s bit at that height on the middle of the trunk.
- Taking a sample at breast height gives you an estimate called the DBH age. You'll need to add 5 to 10 years to the DBH age to estimate the tree’s total age.
- You'll take the sample at breast height because it’s not practical to take one at the tree’s base. Roots, brush, and the ground would prevent you from turning the handle, and it’s hard to drill while crouching or lying on the ground.
Bore just past the trunk’s estimated center point.Apply firm pressure and turn the handle clockwise to drill into the tree trunk. Continue turning until you think you’ve drilled around 2 to 3 in (5.1 to 7.6 cm) passed the pith, or the center of the trunk.
- Calculate the tree’s radius to estimate how far you’ll need to drill. Measure the tree’s circumference, divide by pi (about 3.14) to find the diameter, then divide the diameter by 2 to find the radius.
Insert the extractor, then turn the handle counterclockwise.The extractor is a long tube with teeth at an end. It fits into the augur, or the part that you’ve drilled into the tree. Slide in the extractor, then turn the handles clockwise to remove the instrument and extract a core sample.
Remove the sample and locate the pith, or the center of the trunk.After sliding the core sample out of the extractor, you’ll see an array of curved concentric lines. These are sections of the tree’s rings. You should see a dot at the interior end (opposite the bark end) of the core sample that marks the center point of the concentric rings.
- If you don’t see the pith, place the sample on a large sheet of paper, and extend the curved lines to make full rings on the paper. Based on the rings you’ve drawn, try to guess where the center point would be, and estimate how many rings you’re missing.
Count the rings on the core sample.After you’ve found the pith at the sample’s interior end, count the dark curved lines until you’ve reached the bark end of the sample. Use a magnifying glass if you have trouble seeing tightly clustered rings.
- If you have trouble making out the curved lines, sand the sample to make them more visible. Start with 60-grit sandpaper, then finish with a fine grit, such as 400.
- Remember that your ring count gives you the tree’s DBH age estimate. Add 5 to 10 years to estimate the tree’s total age.
QuestionHow can I know the growth factors of different trees?wikiHow Staff EditorStaff AnswerLook online and enter the keywords "growth factor" plus the species of tree in question. Entering your location might give you a more accurate result. For instance, search for, "Growth rate + sycamore trees + Atlanta, GA." If you can't find good results, us a rough estimate of 3/4 to 1 inch (1.9 to 2.5 cm) of girth growth per year.Thanks!
QuestionHow do I determine the age of a tree?wikiHow ContributorCommunity AnswerCount the rings when it's a stump. Otherwise, you're just going to have to estimate by seeing how thick, tall, and strong it is.Thanks!
QuestionHow old is a tree if it has 10 annual rings?wikiHow ContributorCommunity AnswerA tree typically adds one set of growth rings to the diameter of the tree each year. One light-colored "springwood" ring and one darker, denser "summerwood" ring constitutes one set of annual growth rings. So starting at the center of the tree at ground level, if you counted 10 sets of rings, the tree should be 10 years old. But trees may put on "false rings" during drought events, so unless you have experience interpreting growth rings, a simple ring count can be misleading.Thanks!
QuestionWhat are tree rings made of?wikiHow ContributorCommunity AnswerTree rings are just new growth from the tree. The growth occurs in the cambium (which is the thin, continuous sheath of cells between bark and wood). In spring, the cambium begins dividing, which creates new tissue and increases the diameter of the tree.Thanks!
QuestionWhich ring is the growth ring?wikiHow ContributorCommunity AnswerTree rings are usually composed of alternating narrow, dark rings and wider, light rings. Trees grow fastest in the spring, which produces the wide, light rings. During the summer, trees grow slower, and narrow, dark rings are produced. Each set of rings represents one year's growth for most trees that lose their leaves in the winter.Thanks!
QuestionCan an apple tree be 80 years old?wikiHow ContributorCommunity AnswerYes. Apple trees can live far longer than 80 years.Thanks!
QuestionWhat causes the tree rings to grow unevenly?wikiHow ContributorCommunity AnswerA tree ring's width is determined by how much wider the tree grows in one year. Generally, growth rings are widest in years of high rainfall and narrow in years of drought, when the tree has a disease, or is being shaded by other trees.Thanks!
How do I find the age of a tree by tree rings?
How many annual rings have been found in pins trees?
How can I find out how old a fir tree is?
What is the age of a paper bark tree with an 8 foot girth that is 14 feet tall?
What are factors of tree growth?
To determine the age of a tree, first find its diameter by measuring the circumference of the trunk in inches and then dividing that number by pi. Once you have the tree's diameter, look up the growth factor for the type of tree you're measuring, which is how much width it gains annually. Finally, divide the circumference by the average annual growth rate to determine the tree's age.
- Tropical trees usually don’t produce visible rings, so you’ll need to use other methods to estimate tree ages in locations without a cold season.
- While counting rings is more accurate than other methods, it’s not foolproof. Weather conditions, soil conditions, injury, and other factors may lead to multiple rings in a single year, or no rings at all.
- Taking a core sample injures the tree, but it can heal itself. There are fungicide plugging compounds available designed to promote healing. However, these may actually promote infections, so plugging isn’t recommended.
- Don’t cut down a healthy tree just to find out its age.
- Use caution when handling a borer, saw, or any other sharp instruments.
Sources and Citations
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