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How to Tell a Tree’s Age |
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by Marlin Bowles, M.S.
Plant Conservation Biologist
Michael Jones, Research Associate
Tracing a tree back to its roots has never been simpler. With a newly developed aging chart, the life histories of the region’s old-growth trees are just a measurement away.
The tool in question resulted from a 1996 study of Chicago Wilderness’ old-growth forests. Morton Arboretum researchers Marlin Bowles and Michael Jones calculated the age of trees in Chicago region forests by collecting core samples from about 600 area specimens. The cores provided rings for Bowles and Jones to count without harming the tree. The extractions were only 3/16″ wide so the trees’ living tissue was minimally affected.
Bowles, a plant conservation biologist, says that old forest trees can help nature enthusiasts learn more about the history of their local environment. For example, an area with mostly young trees must have experienced a major logging or fire event that would have eliminated all the older trees. On the other hand, a stand of very old trees means that there has been no disturbance for a long time to cause disturbance to the tree stand.
The study found that the oldest trees in our area, mostly white oaks, date back to the early- to mid-1800s, when settlers began to thin some of the wooded groves in northern Illinois. The data also confirm the conventional wisdom that human fire suppression has caused the number of sugar maples to increase, while oak and shrub populations have declined.
Here’s how to calculate a tree’s age. Warning: It helps to have a little botany background and some math skills!
1. ID the tree species (a tree field identification guide will be helpful).
2. Measure the tree’s circumference with a tape measure. Wrap the tape around the tree at chest height (about 4-5 ft up) to produce an accurate measurement.
3. Divide the circumference measurement by pi (3.1416) to yield the tree’s diameter.
4. Check the chart (below) to determine the specimen’s age.
Was your tree starting out life as DuSable was building the first cabin in Chicago in 1779? Or when Illinois was just becoming a state in 1818? Or was it sprouting from an acorn when engineers reversed the Chicago River in 1900?
This measurement technique is about 90% accurate for forest-grown trees listed on the chart. 
Some trees, because of poor growing conditions, may grow more slowly and, therefore, may be older than their size would suggest. On the other hand, trees grown in the open, like those in a suburban backyard, will be much younger for their size because the added sunlight available to them speeds their growth. Also, as the chart shows, different species grow at different rates.
Want to know more? Try this link. You’ll also find an article authored by Gerry Donnelly, PhD, President and CEO of The Morton Arboretum, on “Plant Science Gardens in Conservation,” in which he explains that botanical gardens and arboreta play a distinctive and integral role in protecting and preserving biodiversity.
Article adapted from “Field Notes” in the Spring 2006 edition of Chicago Wilderness magazine.
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July 24th, 2009 at 8:40 am
I have a Gingko tree in my backyard – the diameter of the trunk is over 11 feet. Do you have a way to calculate the age of a Gingko tree?
July 24th, 2009 at 9:36 am
Now there is, thank you
July 24th, 2009 at 1:50 pm
Hi,
We measured our Burr Oak that lives in our backyard in Naperville. 149 inches in circumference; a diameter of 47. Your chart stops at 39 with an age of 254 years. With our tree coming in at 47, what would be its approximate age? I’ve always wanted to know the age of this particular tree. I was thrilled to get this e-mail from the arboretum. Thank you! Denise Gallagher
July 24th, 2009 at 3:17 pm
Marlin, this is a really interesting study. Do you have a map showing where these forest remnants are? If so, I would sure appreciate a copy so I can take my natural history students to see them.
We have visited an area of Forest Preserve north of the Indian Boundary Golf Course. There are a number of large white oaks in there, and the soil is an undisturbed Alfisol. There is a small unnamed creek that splits the forested area along which skunk cabbage grows. It is a very interesting locality.
John
July 24th, 2009 at 9:15 pm
I would like to know the age of our county’s two most famous trees, the Tivoli Cottonwood, and the Hobson Oak. Also, Mr. Bowles, I believe you were going to take a walk with me to see the state champ Sugar Maple located at Herrick Lake……hopefully before the old wreck blows over! Also, Mr. Bowles, I looked over your paper that was linked to above…….I do prefer oaks over maples, but why would it be a huge concern if maples took over as the dominant tree in our forests?
David
July 27th, 2009 at 1:43 pm
Cat: I’m sorry, but I do not have any information on Ginko trees. Are you sure your tree is 11 feet in diameter, or do you mean circumference?
Marlin
July 27th, 2009 at 1:53 pm
Denise: We do not have any information on burr oaks that large. Burr oaks often grow rapidly if they are in the sun; but, they also tend to grow more slowly as they become larger. So it is difficult to project how old this tree might be. I would have to guess that it is between 250-300 years old.
Marlin
August 2nd, 2009 at 5:52 am
I live in a Northern Floodplain in Libertyville next to a forest preserve. I see large oaks with lots of sawdust at their bases that my landscaper/naturalist told me were from ants. Often these trees drop. Should I report it to the Forest Preserve? Also there are swampy areas which grow marsh marigolds, iris, carex stricta. There are some elms around but I would like to grow and tend to a Ulmus Thomasii, a Rock Elm on my lot. Any suggestions about where I might find one? As a side note, I was happy to read about your efforts to restore the Beach pea at Illinois State Beach – it is a special place.
August 4th, 2009 at 12:44 pm
posted on behalf of M. Bowles:
Paul: I’m sure the Forest Preserve would be interested in your observations. Rock elm would need well drained habitat, and might not grow in a floodplain. I do not know where to obtain one locally; however, you might be able to purchase one over the internet and have it shipped.
Marlin
August 17th, 2009 at 12:42 pm
Thanks for great info!
Do you have any information on DBH and age of Black Oaks? and any thoughts on growth/age in sand dunes?
September 19th, 2009 at 7:30 pm
I am a Webelos leader for cub scouts and have a forestry achievement. I seem to remember as a child seeing a display somewhere of a large tree stump that labeled all the events the tree went through in the years it was around. Has anyone seen this?
July 6th, 2010 at 3:27 pm
My white oak diameter is 69.75″. Your chart stops at 39. What would be the age of this baby?
September 5th, 2010 at 4:27 pm
The species table showing diameter vs age is fasinating. Where can I find this info on other trees such as sycamore and live oak?
October 30th, 2010 at 10:12 pm
I am interested in your table for clculating the ages of trees. Is it applicable to trees grown in Ireland. Also have you any figures for horse chestnut and beech. Thank you for an informative article. Maire Ni Ghruagain
March 7th, 2011 at 9:25 am
Sir, We live in Hambleton North Yorkshire and have a beautiful English oak tree in your garden. It measures 96 inches in diameter. Can you give me an approximate age please?
March 8th, 2011 at 3:56 pm
I suspect that your measurement of 96 inches is the circumference around the outside of your tree. If we convert the masurement to diameter it would be around 30 inches. We have very limited data on the growth of English Oaks; but do have two two on the Arboretum grounds that reached that size (diameter 4.5 feet above the ground) at age 65. Based on the above assumptions, and if growing conditions in your garden are similar to the Arboretum, that would be a reasonable estimate for the age of your tree.
June 7th, 2011 at 6:01 am
I have 2 weeping willow trees on my property which are my prize possessions. Just the other day I measured the diameter of the trunks to apply a weeping beetle pesticide. I always thought the trees were the same age but one appears to be growing and maturing faster than the other. I planted them when they were about 2 years old (I think)and they were just very green and flexible. The more mature tree measured 20″ around the trunk while the other measured 15″ around the trunk. Can you please tell me how old these trees really are? Your chart doesn’t list weeping willow trees.
June 26th, 2011 at 6:43 pm
I have a live oak tree with a circumferance of 18ft 3inches. What would the age of this tree be?
July 1st, 2011 at 3:06 pm
I have silver maple. We measured 163 inches around. We divided by 3.14 and came up with 51.91. Could you give us a good estimate of its age?
July 18th, 2011 at 3:48 am
I have a Burr Oak tree in my backyard in Tower Lakes that measures 15ft.3 inches in circumferance.Could you please tell me how old you think it is.Thanks
August 2nd, 2011 at 6:03 pm
We have a white pine north of Peterborough Ontario. What tree in your graph would be equivalent?
August 30th, 2011 at 1:39 pm
In our park Weeping Willows fell over from winds from Hurricane Irene. How can I tell how old they are, They have been there as long as I can remember!
September 2nd, 2011 at 1:18 pm
We have a big sycamore here in New Jersey, probably among the largest in the state.
When I last measured it several years ago, it was about 5 feet in diameter (183 inches around, measured up 4 feet from the ground).
Here’s a recent photo of it.
https://www.facebook.com/groups/2344729788/#!/photo.php?fbid=2148250519312&set=a.1432569467733.54890.1637791382&type=1&theater
Any guess as to it’s age?
September 23rd, 2011 at 12:13 pm
Greetings,
I have a California Pepper tree that we unfortunately just lost! I’d really like to know the approx. age! It has a diameter right around 50 inches. Could you please figure out the approx. age? Thanks for all your help!
Best Regards from San Diego,
Stephen Kevane
September 29th, 2011 at 8:15 pm
taking down a house,1840,on county reg.,numbering pieces,it’s going back up,red oak 57in.,awesome sight,love VA.
October 3rd, 2011 at 7:15 am
This is a terrrific website. Do I need to adust the tree measurements to determine the age of trees in Washington, DC which has a slightly longer growing season? Thanks very much.
October 3rd, 2011 at 4:34 pm
I also have a silver maple that is 151″ around. I would like to know the approx age of this tree. Please let me know soon. thank you.
Carolyn Clifford
October 11th, 2011 at 7:36 pm
I think some of the posters are missing an important point; this chart is for trees growing in a natural setting, not in your suburban yard. Trees grow faster in your lawn because they get more light.
If you know when your house was built, that will give you a better idea of how old your trees are.
October 20th, 2011 at 12:34 pm
There are a variety of factors that affect tree diameter. Such as but not limited to stand density, crown class, soil type, slope, aspect, growing days, genetics, rainfall, etc. Although interesting, this graph can really only apply to the local conditions in which the study took place.
November 3rd, 2011 at 9:29 am
I live in the Western Reserve area of Ohio.
Next to Mill Creek Park in Boardman,Ohio to be exact. I measured a white Oak tree four feet off the ground as you suggest and got a circumfrence of 165 inches. This would equate to approx.52 inches in diameter.Since your chart only goes to 39 inches how would I best determine the age of this tree?
Thanks
Gary K.
November 3rd, 2011 at 5:14 pm
In response to the question by Gary K., I would suggest having a local forester examine the tree. Our table only applies to forest grown trees, and since the data are from the Chicago region, its difficult to extrapolate to other areas (and larger trees) where growing conditions might be different. White oaks tend to grow slowly, especially when they are large or old, so this might be a very old tree. Neil Pederson has an article (External Characteristics of Old Trees in the Eastern Deciduous Forest, with great photos) in Volume 30 (No.4), pp.396-407 of the Natural Areas Journal (2010). If you can obtain this article, it might be helpful.
November 25th, 2011 at 8:57 am
I HAVE A OAK TREE WITH A 18FT DIA. AT 5FT UP FROM THE BASE. CAN YOU AGE THIS FOR ME YOUR CHART STOPS WELL SHORT OF THIS. THANKS
December 8th, 2011 at 6:04 pm
Rick:
I’m sorry, but since our chart stops short of the size of this tree, its almost impossible to estimate its age. All i can suggest is that it might be older than the maximum estimate on the chart.
Marlin
December 9th, 2011 at 5:46 pm
An oak with an 18′ trunk diameter is too big for our area; I think the writer may mean an 18′ trunk circumference, which would be a more realistic 5.7-foot diameter. That is a large diameter for an oak, but not unknown in our area. The fomula used in the article gives a good working estimate based on an average growth rate for the Chicago region. However, it is an estimate.
Trunk diameter depends a lot on the species of tree, age of the tree and where it is growing. I have two white oak tree trunk sections from the Arboretum that are both about 32″ in diameter. One is 141 years old; the other is 302 years old with virtually the same diameter.
Based on the formula in the article, a 32″ diameter white oak should be about 249 years old. One of my samples is significantly younger than the average, the other significantly older.
The same saying applies to tree diameters and growth rates as well as to home values – growth rates and diameters are based on location, location, location. The only way to accurately assess the age of the tree is to take an increment core sample and count the rings.
Ed Hedborn
The Morton Arboretum
December 19th, 2011 at 11:44 am
Ed:
I’m not sure if you are referring to the formula used in our article, or one used by John Dwyer.
http://treetalk.mortonarb.org/areas-of-interest/do-you-know/what-are-the-ages-of-trees-in-your-neighborhood/597/
Our data, as well as John’s, are actually not based on average growth rates, but on an equation (a power function in our case) expressing the relationship between tree age vs. tree dbh. The actual data and equations are shown in the link below, scroll down to the graphs:
http://plantconservation.us/resources.html#treerings
These equations have r-squared values that range from about 0.87 to 0.90, which means that 87-90% of the variation in the individual tree ages is explained by their diameters. That’s actually pretty good, and means that the equations have strong predictive value. ne reason for this is that the data are taken from forest grown trees, which partition by habitats. As you note, it’s location, location, location.
I keep reminding people that because our data are from forest-grown tree species, they cannot be applied to different species, nor to open grown urban trees, which are usually much younger at a given diameter. John Dwyer has addressed this (http://treetalk.mortonarb.org/areas-of-interest/do-you-know/what-are-the-ages-of-trees-in-your-neighborhood/597/).
I completely agree with you on your example of variation in tree age vs. dbh for white oak. Even for forest-grown trees, our white oak data show a different growth pattern from other trees that we have examined. See the bottom left graph for white oak. It is clear that the age-dbh relationship does not exactly follow the regression line. It actually reaches a plateau at about 150 years beginning at about 35 centimeters, resembling a logarithmic function. If we had tried to get a significant regression only using trees that were greater than 25 centimeters, there would be no relationship and we could not predict tree age.
Nevertheless, there are two 60-centimeter trees that are about 250 years old, further supporting your comments.
Another important point is that it is dangerous to extend tree age estimates beyond the last point on a regression line. We provide estimates of tree ages up to 100 centimeters, but we have no data for trees that large. There are many examples of larger trees out there for many species, but most have rotten cores and cannot be aged, or it is impossible to hit the tree center and get an accurate age. The growth curves of almost every tree species also eventually start to plateau as they get extremely large because proportionally more biomass is required to build a growth ring for a larger tree than for a smaller tree. For this reason, as well as other factors of tree ageing, tree age-size relationships are almost always unpredictable for old growth trees. Attached is a very interesting article, with photos, on characteristics of old growth trees by Neil Pederson.
Marlin Bowles
The Morton Arboretum
January 8th, 2012 at 4:39 pm
My Red Oak has a 55 inch diameter. your chart doesn’t go that high. Can you tell me how old my tree is?
Thanks, Bill Huntley
February 20th, 2012 at 3:30 pm
I live in the Ponderosa Pine forest near Flagstaff, AZ.
Elevation 6900 approx.
A Ponderosa Pine in my front yard measures 96 inches circumfrence at 4 1/2 feet above ground level or 30.58 inches diameter. Pines are not listed on your chart, but can you give me an estimate of this tree’s age? There are about 10 even larger trees on my property. There is one American Elm, a seedling from Minesota that has a diameter of 4.78 inches, (15 inch circum.) I am curious about its age, also. Can you help? Thanks in advance!!!
February 21st, 2012 at 11:44 am
I do not have any information on estimating the age of a ponderosa pine or American elm growing in Arizona. For more information, you could contact the forestry department at Northern Arizona University in Flagstaff.
March 25th, 2012 at 7:10 am
Hi,
I have 3 huge oak trees surrounding my house (hope a storm dont knock them down on us or we are goners). One of the oak trees I measured around the trunk and it 12 foot 8 inches and I dont even know how tall. I dont why I wonder how old it is. I am just curious.
I think I got a number of 45 for your chart but you dont have 45. I dont know about trees to tell you what kind of oak tree. I just know it is an oak tree because everyone who comes to my house says they are jealous of my big oak tree. LOL
April 14th, 2012 at 12:39 am
I’m a forest modeller who came here looking for some data on growth rates for deciduous temperate hardwood trees.
Its great that you are providing this type of information to the public, and I’m very intrigued by the regressions and formulae of age vs time.
The charts I found after following the 2nd link in comment 35 have a series of formulae which are typically something like T=5*D^0.8 where T is time (age) and D is diameter in centimetres. That can be re-arranged with a little algebra, into D=0.2*T^1.25
Now what that seems to mean, with an exponent (power term) of more than 1.0, is that trees are actually growing faster and faster as they get older !! That’s very counter-intuitive. However since the plotted data came from different trees, not the same trees over time, I can only conclude that the trees in the past were growing at a much, much faster rate than the trees at present. In other words when those older trees were say 50 years old, they were already much bigger than the current crop of trees of that age.
I note the Bowle & Jones 2008 paper suggests that the forests in the past were much more open-canopied, so this presumably produced the faster tree growth, despite droughts etc. However their ring width data in the Appendix, if I am reading it right, doesn’t really support that conclusion. So what’s going on?
As trees age and increase in size (diameter), their annual growth ring width declines. Even if the area of new sapwood is constant each year, it’s an ever-thinner ring around an ever-larger circle. Hence the trees that are more than say 20-30 years age and still growing slowly, are very unlikely to pick up growth in old age so as to recover what they missed out on in their youth.
So, if the modern trees are being suppressed by excessive canopy, and the diameter vs time charts are correctly drawn, then it looks to me like if you want have any big trees at all in your Chicago area forests in the future, you’d better get out the axe and firestick and start thinning out the patches where the young trees are, and give them a chance to get going with a full head of steam!
May 3rd, 2012 at 12:07 pm
Have an oak tree here on the Brazos River in Texas measures 134 inches around. What would be approx age?
Thanks