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How Old Are Trees

How Old Are Trees

Introduction: (Initial Observation)

Some trees are small and some trees are big. Obviously trees grow as they age; but how do you tell how old a tree is?

Can you use the height of a tree as an indication of its age? If so, how do you measure the trees’ height?

The age of trees are important for many different reasons. Each tree carries a history of weather conditions, accidents and human activities around itself. By investigating a tree, we can learn about some events in the past.

In this project you will study some trees in your area to determine their age. Can you guess who planted the tree by knowing the age of the tree and its location?


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

This project includes 3 experiments. Most students select only one experiment to perform. You may want to try more than one experiment.

Information Gathering:

Find out about trees’ life and growth. Read books, magazines or ask professionals who might know in order to learn about the effect of aging on trees. What things change on a tree as it grows? Keep track of where you got your information from.

Following are samples of information that you may find.

Trees start off as seeds and take many years to grow to their full height. If they are damaged, they take a long time to die. This can be such a long time that people have forgotten how they were damaged in the first place.


What kind of tree is it?

This can be difficult, but there are several tree books in each local library that you could look in. You may also find some information sheets.

It is quite important to try and answer the following questions.

a. Is it a conifer, like a Christmas tree, an evergreen, like Holly, or a deciduous tree like an Oak?

(Deciduous trees drop their leaves in autumn and produce fresh ones in spring)

b. What are its flowers and fruit like?

c. What is its bark like – rough, smooth, lined, lumpy?

d. What kind of tree do you think it is?

e. How old might it be?

f. Was it planted or did it grow by chance?

g. How tall is it?


Why is it important to know the age of a tree?

You may ask this question from many different people and get many different answers. In other words there are many reasons that the age of trees are important.

Most of these reasons have to do with growth rate, fruit bearing, and maintenance cost of trees in different ages.

Tree age is one of the factors to take into consideration when evaluating the horticultural and economic potential of a block of orchard.

For example apple trees with the age of 4 to 15 have the highest yield and are the most valuable. Trees that are much younger or much older are not as valuable because of lower yields.

The age of the tree can be approximated by using the measuring tape to obtain the girth of the trunk at a point five feet above the base of the tree. This number in inches is basically the age of the tree but bear in mind that this method does not work on saplings (young trees).

In a woodland a tree increases its girth by an average of 1.25cm per year. In an open situation a tree increases its girth by approximately 2.5cm per year.

If you wish to allow for the differing growth of different species, a list of the average increase in girth per year of a variety of species is given below:

1.88cm for oak
2.50cm for hazel
2.75cm for sycamore
1.25cm for holly and yew
3.13 for pine and spruce

The width of the ring in different mature trees are measured and provided as samples to justify the method of estimating tree’s age by the girth or by the diameter. See the table here.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is to determine the ages of some trees in our local area.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

Independent variable is the girth of the tree at a certain height.

Dependent variable is the age of a tree.


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis. This is a sample hypothesis:

My hypothesis is that the girth of trees (the distance around the tree trunk) increase with any increase in the trees age. In other words we can measure the distance around the tree trunk and use it to estimate the age of any specific tree.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

Experiment 1:

Measure the girth of a tree and use it to estimate the age of the tree.

Introduction: As trees grow, the trunk gets thicker. So the older the tree, the greater its girth. On average, trees increase their girth by 2.5cm a year.


1. Measure the distance around a tree trunk. This is its circumference or girth.

To do this, take a measuring stick or meter ruler and a tape measure out with you.

Measure 1 meter up the trunk from ground level.

Put your tape around the tree at this height and record the distance round the trunk.

Repeat this for several trees. Are they all the same age?

* It is commonly suggested to measure the girth of a tree at 4.5 feet height or 135 centimeters. I modified this because many young students are not able to reach to that height.

If your measurements are in centimeters, divide the measurement by 2.5cm. This will give you the rough age of your tree in years.

For example:- If your tree measures 1.5 meters round its trunk, change the measurement to centimeters by multiplying by 100.

1.5 x 100 = 150

Now divide the measurement in cms by 2.5

150 / 2.5 = 60

This means your tree is about 60 years old!

If your measurements are in inches, the same number indicates the rough age of the tree. For example if the tree’s girth is 45 inches, this means your tree is about 45 years old.

Links related to measuring the girth of a tree.



Make a data table:

Number the trees you measure their girth and record their estimated age in a data table like this:

Tree Number Location Trunk girth Estimated Age
1 At home, in the backyard 73 cm 29 years
2 Entrance of the city park on the left …. ….

If you use the metric system for your measurements, then you must write the girth in centimeters. If you use the English system, then you measure the girth in inches, so you will not need to divide it by 2.5. The same number will also be the estimated age. For example if the girth is 29 inches, then the tree is about 29 years old.

Experiment 2:

Measure the height of a tree

Introduction: The height of a tree cannot be used to determine the tree’s age; however, we may need to measure the tree’s height for other reasons. One way of finding the height of a tree is to climb the tree and drop a ball of string to the ground! This is not a good idea, as you could fall and the string might not fall straight. There are ways of doing this without leaving the ground.

Procedure 1:

The length of the shadows change during the day. In the morning our shadow is long. It becomes shorter as sun rises above the sky. At noon time we have the shortest shadow. After noon shadows start to get longer again.

At least twice each day, there is a moment that your shadow is as long as you are.

That is the time that you can measure the length of shadow of a tree on the ground. The length of shadow at that time is the height of the tree.

Procedure 2: (a different method that is not depended on shadow)

Get a ruler (or a straight stick) and a tape measure, then go to your tree. Start from the side where there is a clear space, because you need to walk away from the tree. Make sure that you will not be walking into the road!

Walk backwards away from the tree, holding the ruler upright at arms length.

STOP when the tree appears to be the same height as the ruler.

Now turn the ruler sideways until it is parallel with the ground. Keep one end on the apparent bottom of the trunk.

Get your partner to walk sideways from the tree (not towards you!), until he/she is level with the end of the ruler. Shout to him/her to stop.

Now measure from your partner to the base of the real tree. This is the rough height of the tree.

X = height of tree

Make a data table:

Number the trees you measure their height and record your data in a table like this:


Tree Number Location Type Height
1 At home, in the backyard Pine 16.5 m
2 Entrance of the city park on the left ….

If you use the metric system for your measurements, then you report the height in centimeters or meters. If you use the English system, then you measure the height in feet and inches.

Experiment 3:

Measure the age of a tree by counting the rings

Introduction: When you cut a tree and look at the cross section of the stem, you will see many rings starting from the center of the circle and going all the way to the sides. These circles represent variations in growth rate that happen in different seasons. In spring trees have a higher growth rate so the cells are larger. In the end of summer growth rate will reduce so the cells become smaller. Finally, in winter most trees stop growing. This method of determining the age of a tree is best after you cut a tree. You can use this method to determine the age of a tree or a branch of a tree.


Find a tree or a branch of a tree that is cut and you can view its cross section.

Count the number of rings from center to one side. How old is this tree or branch of a tree?

Count the number of rings from center to another side (opposite side). Are the number of rings the same in two different directions?

Trace some of the rings. Are all rings complete?

Measure the thickness of each ring. Do all rings have the same width? Does the growth rate of a tree change during its long life?

At what ages does your tree have its highest growth rate?

If you see the cross section of a tree that is 300 years old, can you determine the changes in climate in the past 300 years? Can you determine the years that the tree experienced drought and the years with high amount of rain?

Materials and Equipment:

Material that you need depends on the experiment that you choose to perform. See the above experiments to see what material you need and then write down the list of material in this section.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.


All required calculations are described in the experiment section.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.