Measuring Tree Age
Teacher Instructions
Introduction:
The age of trees can be determined through several methods. The easiest way to
determine tree age is to find a recently-cut stump that has visible growth rings and count
the rings. However, it is usually hard to determine how long stumps have been there. If a
more accurate measure of the age of a living tree is desired, a tree increment borer is the
best tool. A tree increment borer is a tool that includes a handle, an auger and an
extraction rod, called a spoon. The handle and the auger fit together to form a T-shaped
hand drill. The auger is hollow, so that when it's drilled into a tree, a core of wood is
forced into the interior of the tool. The wood core can then be removed by sliding the
spoon between the core and the inner surface of the auger. Tree borers come in various
lengths, and are capable of obtaining corresponding lengths of tree growth. The
measuring of tree age is a labor-intensive and slightly destructive process. It is best if you
choose a “representative” tree or “site tree” to determine tree age. This tree should be of a
species that is dominant in the forest. You will have a much tougher time coring
hardwood species, and it is recommended that you avoid it. You may need to gain
permission before conducting this protocol.
After completing this protocol, students can calculate the growth of the tree by graphing
diameter and ring width. This data can help you get an idea about the growth and age of
the stands on your study site. This protocol along with the other Forest Protocols can
help you gain a better understanding of the trees on your study site. Previous to doing
this activity, students should have selected and marked their team’s study sub-plot.
Objectives:
1) Select trees on study site
2) Use tree increment borer
3) Determine age of tree
4) Graph diameter and ring width
Students Required: Groups of four
Estimated Time: 2 - 55-minute class periods
Overview of Tasks:
*** Decide which trees will be used in protocol. Mark and record on site map.
Day 1
1) Divide class into groups of four, giving each group the location of the tree.
2) Allow students to select role:
Lead Researcher: This student is responsible for coring the tree.
Recorder: This student is responsible for recording the data.
Reporter: This student is responsible for sharing data and collecting classmates
results.
Assistant: This student is responsible for assisting throughout the protocol.
3) Read over student instructions as a class.
4) Allow student to follow the student instructions for Day 1.
5) Spray the samples lightly with a water bottle (this allows the rings to stand out)
6) Store core samples in a safe place, making sure the students mark their tubing or
straw.
Day 2
1) Review the day’s tasks.
2) Allow students to follow student instructions for Day 2.
3) Have students write a lab report in whatever format works best for your class.
Work Safety:
All students should wear clothes and gear appropriate for field work in the woods. At a
minimum, this includes hiking boots or sturdy shoes, long-sleeved shirts and long pants,
rain gear, and a hat. Anti-tick and mosquito repellents may be applied as needed.
Optional
Review the following vocabulary:
Site tree, tree increment borer, spoon, auger, earlywood, latewood, and pith
Measuring Tree Age
Student Instructions
Introduction:
The age of trees can be determined through several methods. The easiest way to
determine tree age is to find a recently-cut stump that has visible growth rings and count
the rings. However, it is usually hard to determine how long stumps have been there. If a
more accurate measure of the age of a living tree is desired, a tree increment borer is the
best tool. A tree increment borer is a tool that includes a handle, an auger and an
extraction rod, called a spoon. The handle and the auger fit together to form a T-shaped
hand drill. The auger is hollow, so that when it's drilled into a tree, a core of wood is
forced into the interior of the tool. The wood core can then be removed by sliding the
spoon between the core and the inner surface of the auger. Tree borers come in various
lengths, and are capable of obtaining corresponding lengths of tree growth. The
measuring of tree age is a labor-intensive and slightly destructive process. Make sure to
follow the student instructions and your teacher’s instructions. Your teacher will be
selecting the trees that you will be measuring. Previous to doing this activity, students
should have selected and marked their team’s study sub-plot.
After completing the student instructions, you can calculate the growth of the tree by
graphing diameter and ring width. This data can help you get an idea about the growth
and age of the stands on your study site. This protocol along with the other forest
protocol can help you gain a better understanding of the trees on your study site.
Materials:
Day 1
Site Maps
Tape measure
Tree increment borer
Straw or 3/8” piping of adequate length
Day 2
Core sample
Ruler
Hand lens
Solid-colored piece of paper
Tape
Data sheets
Procedures:
Day 1
1) Make sure your class has set out the transect, and your team has set out its sub-plot
before proceeding. Decide how many trees you will need to sample to get the
information you need to answer your research questions.
2) With your materials go to your team’s sub-plot at the study site that you will be
sampling, in your groups of four decide on the following roles
Lead Researcher: This student is responsible for coring the tree
Recorder: This student is responsible for recording the data.
Reporter: This student is responsible for sharing data and collecting classmates
results.
Assistant: This student is responsible for assisting throughout the protocol
3) Locate the tree you will be measuring on your study site map.
4) With your group, and materials for Day 1, locate the trees to be sampled.
5) This is a delicate process, so work as a team and BE CAREFUL!
6) Follow the student instructions below:
A. Find a flat surface on the tree at 4.5 feet (1.37 m) above the ground that is in
an accessible location. Remove the spoon from the auger and put it
somewhere you know you will find it (have a group member hold it), and
remember not to step on it.
B. To ensure that the pith of the tree is intersected, position the auger on the bark
so that the axis of the borer will pass through the center of the tree.
While holding firmly and pushing toward the center of the tree, turn the borer
clockwise several times very slowly with one hand on the auger near the tree,
and the other hand at the very top of the auger, until the threads penetrate solid
wood for at least an inch, or until the auger will support itself during this
initial stage of coring. Try to maintain the angle of the auger toward the
center of the tree. Once the auger will support itself, continue turning the
auger until it reaches the center of the tree, or until it can no longer be turned.
C. Insert the spoon into the auger carefully, with the empty U-side up. Press
gently but firmly until the spoon is completely inside the borer. Take care to
not bend the spoon. Once the spoon is all the way in, turn the auger one (and
only one) full turn counter-clockwise. This will break the core off inside the
spoon.
D. Carefully and slowly remove the spoon. The core will come out balanced on
top of the spoon. Be aware while removing the spoon, that the core can easily
fall and break. Once the core and spoon are completely removed from the
auger, the core should be carefully inserted into an adequate length of
3/8”plastic tubing (or straw) for further analysis.
7) Return to the classroom. Allow your instructor to spray your sample. Return the
sample to the straw or tubing making sure to mark the tube to identify later for
analysis.
Important Information:
Each ring consists of a light layer of early wood and a darker layer of latewood. The ring
is distinguished by the abrupt end of the previous year’s darker latewood, and the next
year’s lighter early wood.
Day 2
1) In your group, obtain your sample and materials for Day 2.
2) Tape the solid-colored piece of paper on a flat surface such as a desk or countertop.
3) Tape the ruler on top of the paper.
4) Lightly tape the sample on top of the ruler so that the zero is at the “pith” or tree
interior end.
5) If the rings are close together, a hand lens may be used. Use the data sheet to record
the number and width of rings.
6) Start at the interior end of the core (this should start at 0 on your ruler). Have one
person read off the progressive lengths along the ruler that correspond to the rings.
For example, if the 1st ring ends at 2 mm, record 2; if the second rings ends at 4 mm,
record a 4. Repeat this process until you reach the bark layer.
7) The number of rings you counted is the age of your tree, plus, you need to add the
time it took for the tree to grow to 4.5 feet tall, roughly 5 years, before it began to
grow rings. So your tree age is the number of rings plus 5.
8) Using a line graph, graph the diameter of the tree (ring width times two), using the
graph that is provided. Make sure to fill in the X axis and Y axis and label
accordingly. Remember you will be starting with year 5. There is a sample graph
that is also provided.
9) Using a line graph, graph the ring width of the tree, using the graph that is provided.
Make sure to fill in the X axis and Y axis and label accordingly. Remember you will
be starting with year 5. There is a sample graph that is also provided.
Tree Age and Growth
Data Sheet
Site or Subplot______
Tree Species______________________
Tree Age______
Ring
from
Pith
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Length
From Pith
(mm)
Ring Width
(mm)
Tree
Diameter
(mm)
(ring width
X 2)
Comments
Diameter Over Time
Example and Analysis:
Note that the tree was cruising along in growth until 18, where it flattens out a bit. Age 18
is likely when “crown closure” occurred—trees in the stand grew up big enough around
each other to begin touching or overlapping branches. Light levels reaching the lower
leaves on the tree begin to decline at this point, so that they do not photosynthesize as a
whole tree as much as they did when all of their leaves were exposed to full sun, earlier
during stand development.
Annual Growth Over Time
Example and Analysis:
A sudden rise in growth rate, like this tree experienced in year 21, may result from the
death of a neighboring tree that no longer shades or competes for water, some other kind
of thinning event, or fertilization of the stands, as is sometimes done to boost tree growth.
Diameter Over Time
Student Graph
Name_________________________
Tree Species_______________________
Tree Age_____
Diameter (cm)
______________________________________________________
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______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
What does this graph tell you?
How do you know?
Ring Width Over Time
Student Graph
Name_________________________
Tree Species_______________________
Tree Age_____
Ring Width (cm)
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
What does this graph tell you?
How do you know?