How to Determine the Age of a Tree

We can estimate the age of a tree fairly quickly and accurately by looking at certain characteristics. For example, depending on the type of tree, you can measure the circumference of the trunk or count the rows of branches. The most accurate method is to count the circles on the cross-section of the trunk, but this only works when the tree has been cut, and you can’t cut down a healthy tree just to determine its age. Instead, you should try a different method or a combination of methods to get an accurate estimate.

Table of Contents

Estimate the age of a tree by measuring the trunk circumference

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Measure the trunk circumference at chest height. The average chest height as measured in forestry is 1.4 meters from the ground. You can wrap a tape measure around the trunk at this height and record the trunk circumference measurement. ^{[1] X Research Source}

For sloping ground, you need to measure to a height of 1.4 m from the ground on the high ground side, mark again, then measure the same on the low ground side. Average bust height is the midpoint of these two measurements.
For trunks with a fork at a height of less than 1.4 m, measure the circumference just below the fork.

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Find the diameter and radius of the trunk. To find the diameter, you would divide the circumference by the number pi (approximately 3.14), followed by finding the radius by dividing the diameter in half. ^{[2] X State of Michigan Trusted Source Go to Source}

For example, if the circumference is 390 cm, the diameter will be approximately 120 cm, and the radius will be about 62 cm.

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Subtract 0.6 cm to 2.5 cm of bark. For trees with thick bark like black oak, you need to subtract the radius measurement by 2.5 cm. Subtract 0.6 cm for thin bark species such as table maple. If you’re not sure how thick or thin the bark is and just need an approximation, you can subtract the radius measurement by 1.3 cm. ^{[3] X State of Michigan Trusted Source Go to Source}

If you include the bark, the measurement of the trunk circumference will be larger and the results will be skewed.

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Use similar fallen trees to calculate the average width of the circle across the trunk cross-section. Look around to see if there are dead or felled trees of the same species as the tree you are trying to age. If you find a tree that can see circles in its trunk, measure the radius and count the number of rings, then divide the radius by the number of rings to calculate the average ring width. ^{[4] X Trusted Source State of Michigan Go to Source}

Assuming a nearby tree stump has a radius of 64 cm and you count 125 rings, the average ring width will be 0.51 cm.
The growth rate will vary by plant species and environmental conditions. The living tree you want to age probably also grows at the same rate as trees of the same species that grow nearby.
You would substitute the measure of the width of the circle in the trunk (or the average growth rate if there are no stumps nearby) into the equation for the age of the tree.
Even if you already have a width measurement, you can use the average growth rate to calculate the age of the tree, and then compare the results of the two methods.

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Look up the average growth rate of the tree species, if necessary. If you can’t find a stump or fallen tree nearby, you can go online to find the average growth rate of the tree species you’re trying to age. You should also enter the location in the search keyword for more accurate results. ^{[5] X Research Sources}

For example, oak, ash, beech, and sycamore have a circumference increase of about 1.3 cm -1.9 cm per year. If you don’t know to which species the tree is age, you can substitute both the numbers 1.3 cm and 1.9 cm into the equation to calculate the approximate age of the tree.
For a more accurate calculation, you should also take into account the location of the tree. In open conditions, the growth rate of the tree is usually faster, about 1.9 cm – 2.5 cm per year. Trees will grow more slowly in urban areas and dense woodlands.
You need to understand how the growth rate is calculated. Many information sources calculate growth rates based on how the circumference increases each year. However, you can find the growth rate based on the average ring width of the radius.

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Divide the radius by the average ring width. If you are using a nearby stump to calculate the average ring width, divide the radius of the tree you want to age by the average ring width. ^{[6] X Trusted Source State of Michigan Go to Source}

Let’s say, minus the bark, the tree you’re trying to age has a radius of 60.96 cm. Using a root of the same species that grows nearby, you calculate an average ring width of 0.508 cm.
Divide 60.96 by 0.508, we get the estimated age of the tree is 120 years.

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Divide the trunk circumference by the annual growth rate. If you find the annual growth rate based on the circumference, divide the trunk circumference by the growth rate. ^{[7] X Research Sources}

Assuming the tree’s circumference is 391.16 cm and its growth rate is between 1.905 cm and 2.54 cm per year, you would divide 391.16 by 1,905, then divide 39.16 by 2.54. The estimated age of the tree will be 154 to 205 years.

Count the number of tree branches

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Count the number of twig rings to estimate the age of conifers. Branch rings are rows of branches that grow from the trunk of a tree at the same height. The twig ring method can be used to calculate the age of conifers or evergreens, but is not very useful for broadleaf trees such as oaks or sycamores. While not as accurate as counting the rings in the trunk, it is a way to calculate the age of a tree without having to cut down or injure the tree. ^{[8] X Research Sources}

Conifers grow annual rings of branches in regular waves. Deciduous or broadleaf species have irregular rings of branches, making it difficult to count accurately.
Counting branches on young conifers is easiest. You will hardly see the tops of tall mature conifers, and older trees also have a more irregular branching pattern.

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Count the rows of branches that grow at the same height. At the base of the tree, look for a row of branches that grow at the same height, followed by a stem without branches, then another row of branches. Keep counting like that until the end of the tree. ^{[9] X Research Source}

You can see 1 branch growing between 2 rows of branches close together. These are the branches that don’t grow out of a regular pattern, possibly due to damage to the tree or unusual weather conditions that year, so don’t count these branches.

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Count the nodes or nodes at the bottom of the stem. Check below the first row of branches for traces of previous shoots. Look for knots and nodules on the trunk where branches used to grow. You will also count these nodes and nodes as branches. ^{[10] X Research Source}

For example, suppose your tree has 8 distinct rows of branches. Below the first row, you can see several eyes sticking out of the trunk at the same height. There is also a row of 2-3 nodes under the eye of that tree. You will count these nodes and nodes as rows of branches, so you will have a total of 10 rows of branches.

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Add 2-4 years of seedling growth. The tree will germinate and grow into a seedling for several years before starting to grow rows of branches. You need to add another 2-4 years to the number of rows of branches counted to include the early stages of the tree. ^{[11] X Research Source}

If the number of rows of branches is 10, the final estimated age of the tree will be 12-14 years.

Count the circles on the stump section

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Check for circles on the cross section of the stump. The number of rings on this stump will indicate the year the tree has lived. You will see dark circles and lighter bands; 1 year of plant growth will include 1 dark color ring and 1 light color ring. Dark rings are easier to distinguish, so you should count these rings to estimate the age of the tree. ^{[12] X Research Source}

The circles in the trunk can also tell about the environmental conditions of a particular year. Thinner rings will indicate cooler and drier years, thicker rings indicate better growing conditions.

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Sand the stump to see the rings better. If the trunk circles are difficult to see, sand the stump cut with a coarse 60-grit sandpaper, followed by a very fine sandpaper, such as 400-grit. You can also see the rings more clearly if you spray some water on the base of the tree. ^{[13] X Research Source}

Some rings may be too close together to be seen clearly. If necessary, you should use a magnifying glass to see more clearly.

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Count the circles from core to shell. Find the tree core, i.e. a small circle in the middle of the concentric circles. Start counting from the first dark ring around the core. Continue counting until you reach the bark. The last ring is usually close to the case and hard to see, so be sure to include this. ^{[14] X Research Source}

If you find it difficult to follow, you can use a pencil to write numbers or marks every 10 rounds.

Count the rings on the drill core sample

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Sampling cores of live plants with growth drills. To accurately estimate the age of a living tree without killing the tree, a drill is used to take a core sample. The growth drill is a T-shaped device consisting of a drill bit and a sample retractor attached to the drill bit. The end of the T is the handle for you to drill into the tree. ^{[15] X Research Source}

The length of the drill should be at least 75% of the trunk diameter. You can find growth drills online or at forest supply stores.

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Drill into the trunk at chest height. Measure to a height of 1.4 m above the tree trunk from the ground. Place the drill at this height in the middle of the trunk. ^{[16] X Research Source}

The method of sampling from chest height will give an estimated result called DBH age. You will need to add 5-10 years to the DBH age to estimate the age of the tree.
You will sample at chest height because it is difficult to sample at the base of the tree. Roots, bushes and the ground make it difficult to turn the handle, and it can be difficult to drill when you have to crouch or lie on the ground.

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Drill just enough through the midpoint of the stem. Press firmly and turn the handle clockwise to drill into the stem. Continue spinning until you guess that you have drilled through the core of the tree about 5cm-7.5cm. ^{[17] X Research Source}

Calculate the radius to estimate the depth to be drilled. Measure the circumference of the trunk, divide by pi (about 3.14) to find the diameter, then divide the diameter by 2 to find the radius.

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Attach the sample draw tube to the drill, then turn the handle counterclockwise. The sample tube is a long tube with teeth at the end of the tube, which is attached to the drill bit, which is the part you just drilled into the tree. Attach the sample draw tube, then turn the handle clockwise to remove the instrument and withdraw the core sample. ^{[18] X Research Sources}

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Take a sample and determine the location of the core, i.e. the midpoint of the stem. After taking the core sample out of the sample tube, you will see a series of concentric curves. This is part of the trunk circles. You should see a dot at the inner end of the tree (opposite the bark tip) of the core sample, which is the midpoint of the concentric circles. ^{[19] X Research Source}

If the core is not visible, place the pattern on a large sheet of paper and use a pen to extend the curves into circles on the paper. Based on the circles just drawn, you can guess the position of the midpoint and estimate how many loops are lost. ^{[20] X Research Source}

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Count the loops on the core sample. Once you have found the core of the inner end of the sample, count the dark curves up to the bark tip of the specimen. Look with a magnifying glass if the rings are too close together for you to see. ^{[21] X Research Source}

If you find it difficult to count curves, you can sand the pattern for a clearer look. Start with 60-grit sandpaper and finish with fine sandpaper, such as 400-grit. ^{[22] X Research Source}
Remember that the number of circles counted will indicate the DBH age of the tree. You need to add another 5-10 years to estimate the final age of the tree. ^{[23] X Research Sources}

Advice

Tropical tree species do not produce pronounced circles, so you need to use other methods to calculate the age of trees in regions where there is no cold season.
Although more accurate than other methods, the method of counting rings in the trunk is also not perfect. Weather conditions, soil, injury, and other factors can cause a tree to produce many or no rings in a year.
Core sampling will damage the tree, but the tree will heal on its own. There are fungicides on the market that are specially formulated to heal plant wounds. However, these products have the risk of making plants susceptible to infection, so they are not recommended. ^{[24] X Research Source}

Warning

Use caution when handling drills, saws, or any other sharp tool.
Do not cut down healthy trees just to determine the age of the tree.

Steps