AMY E. BOYD AND JIM COOPER
Abstract. Tree rings can be used not only to look at plant
growth, but also to make connections between plant growth
and resource availability. In this lesson, students in 2nd-4th
grades use role-play to become familiar with basic requirements of trees and how availability of those resources is
related to tree ring sizes and tree growth. These concepts
can then lead into studies of ecology and further inquirybased investigations.
Key words: ecology, plant growth, resources, role-playing,
tree rings
'hen working with students in outdoor educational
programs, we have found that nothing will inspire as
much awe for plants as getting students to lay down at
the base of a very large tree {such as the one in Figure I)
and look up. Often, once the "wow"s and "awesome's die
down, what follows is a stream of questions: How old is it?
How does it get to be this big? Why aren't other trees this
big? Questions like these, stemming from student experience and curiosity, are what we try to use as the basis for
effective science learning. We share with you here a lesson
that will provide students an opportunity to learn more
about the connection between resources and tree growtb
using a common scientific research tool: the counting of
tree rings.
AMY E. BOYD is a professor of hioiagy. environrnenltil studies,
and .science education at Warren Wilson College, Asheville, North
Carolina. While Dr. Boyd's main focus is college-level science
teaching, she is also involved in preser\ice teacher training, outreach to local schools, and research and service with the local
branch of the Nature Conservancy.
FIGURE 1. The General Sherman tree, a giant sequoia in
Sequoia National Park, is the largest (by volume) tree
known in the world. (Photo by Mark V. Brenner)
JIM COOPER is a recent graduate of Warren Wilson College.
Asheville. North Carolina, His aspirations involve teaching in
local .schools and, eventually, opening an after school program
with a focus on environmental education and child empowerment.
The purpose of this lesson is to (a) familiarize students
with the basic requirements of trees and {b) to allow them
17
18
SCIENCE ACTIVITIES
Vol. 41, No. 3
Dendrochronology is the field of studying tree ring data.
Tree rings have been used to study local environmental history including fires and disturbances, as well as regional
and global climate history. In the classroom, we can use tree
rings as a pattern to help students understand the connection
between resource needs of plants and plant growth.
This activity is designed for 3rd-grade students, but could
be used successfully in 2nd-4th grades. All acfivities can be
done in a standard classroom and can be completed in 1
hour.
MATERIALS (FOR A CLASS OF 20 STUDENTS)
FIGURE 2. Cross-section of the trunk of a very young
balsam fir ^Abies balsamea^, showing 12 growth rings.
Photo © H. D. Grissino-Mayer.
opportunity to role-play the life of a tree by engaging in
competition for resources as would happen in a forest. Students will also (c) learn to recognize the correlation
between years of highly available resources to meet tree
requirements and increased tree growth through changes in
yearly growth ring size. These activities can set the stage for
further inquiry-ba.sed investigations that can be guided by
student-generated questions and interests.
Paper
Pencils
Chairs
Utility lamp
Poker chips in 3 colors (120 or so)
20 cups
10 drinking straws
10 coffee stirrer straws
Water
10-20 cross-sections of small trees (disks I^-l inch
thick)
20 hand lenses or magnifiers
PROCEDURE
Preparation
Plug in utility lamp and make sure the cord is long
enough to reach easily to the area where students will be
working. Fill cups of water and place them on a tray for
distribution.
BACKGROUND
Trees in temperate regions have annual cycles of growth,
with rapid growth in the spring, slower growth in the summer, and little or no growth during the fall and winter.
Because of this cyclical pattern, the woody trunks of trees
record a pattern of annual growth in the form of growth
rings that are visible in the cross-section of tree trunks (Figure 2). Therefore, you can determine the age of a tree by
counting the rings in a tree trunk. This ring counting is particularly dramatic when the tree is cut down, but it can be
done in living trees by boring a thin core into the tree's center and then counting the rings within that core sample (Figure 3).
Age is not the only information you can gather from tree
rings; you can also determine years of high or low growth
based on the size of the rings (wide rings = high growth
years; narrow rings = low growth years). These variations in
growth are due to environmental factors and are usually
intluenced by rainfall, but they may also be signs of variation in nutrient availability, sunlight, or temperature.
FIGURE 3. Increment cores taken from Douglas fir trees
fPseudotsuga menziesii^ growing at El Malpais Nationai Monument (photo © H. D. Grissino-Mayer). The "18"
on the side of the cores shows the location of the year
"1800." The dark iines connect narrow and wide rings,
demonstrating crossdating between the trees.
SCIENCE ACTIVITIES
Fall 2004
Part 1: Observations of Tree Cross-sections
1. Distribute tree cross-sections to the class, so that each
student or group of 2-3 students has one to examine closely.
2. Ask them to observe the tree section tor a tew minutes
and take notes on what they notice about the tree section.
3. Solicit observations from the class as a whole and create a class list on the board.
4. Now focus tbe students' attention on the fact that the
tree cross-sections have concentric rings (hopefully, a student will have observed this characteristic and contributed it
to the class list of observations). Explain to the students that
each ring indicates a year of growth for the tree and that
they can determine the age of a tree by the rings inside its
trunk.
5. Distribute hand lenses/magnifiers and show students
bow to use them. Ask them to count tbe rings in their tree
sections, using the magnifiers as needed. If your tree sections are from different trees, you may then wisb to create a
graph of tree ages, like the one in Figure 4. (If they were all
from the same tree, they would be the same age and therefore a graph would not be very interesting.)
Part 2: What Do Trees Need to Grow?
'ciion
1. Have students brainstorm again to create a class list of
the things that trees need to grow (water, sunlight, nutrients,
air, etc.). If they are not familiar with the term "resources,"
introduce it to them now: the things that a plant or animal
needs from its environment in order to survive and grow are
resources.
2. Ask students to look at tbeir tree sections carefully. Do
they see any difference in tbe size of the rings? Explain to
them that the size of tbe ring indicates the amount the tree
grows. Fatter rings are created in years of strong, rapid
growth when the trees have plenty of everything they need,
and thinner rings represent years when the trees may be lim-
54-
lA
Number o
u
32I •
U-J
6
1l l
7
8
y
Age (years)
•
11 1•
11
10
II
FIGURE 4. The number of tree cross-sections of different ages as determined from counting tree rings.
19
ited in resources. Ask students if they can come up with
things that would keep a tree from getting all the resources
it needs.
3. Give each student a piece of paper and a pencil or
crayon. Ask them to draw a cross-section of a tree on their
paper that is the same age as tbey are (i.e.. students who are
8 years old will draw a tree cross-section with eight rings).
Ask them to leave plenty of space outside their drawing
because tbey will be adding more rings later,
Part 3: Competition for Resources
Tree Life, Year I: Looking ai the Effect of Sunlight on
Growth
1. Get students to stand in an area clustered together.
Have some students represent tall trees by standing on
cbairs and spreading their arms out. A second group of students will represent medium-sized trees and should stand
on the ground and spread their arms balfway out. A third
group represents young trees and should sit on the floor
cross-legged. These groups should be mixed together, so
tbat the tall trees are overshadowing tbe shorter trees.
2. Ask students to hold their positions (trees can't
move!). The teacher then turns the overhead lights out,
draws the window shades, and turns on tbe lamp. You may
-Stand on a desk so tbat you can hold the lamp over the students to simulate sunlight. Ask students, while they are
standing there, which ones are receiving lots of light and
which ones are getting little light. Have them go back to
their cross-sections and add a new ring to their drawing,
creating a fat ring if they received lots of Ugbt and a thin
ring if they received little light.
Tree Life, Year 2: Looking at the Effect of Nutrients on
Tree Growth
3. Now ask students to stand somewhere in the classroom
(clustered), again to represent trees (though this time they
will all be the same size). Once students are situated, spread
poker chips on the floor randomly around the student-trees.
Explain as you do so that these chips represent nutrients in
the soil, and their colors indicate what kind of nutrient: white
for phosphorus, blue for nitrogen, and red for potassium.
Explain tbat in tbis year of the tree's growth, each tree must
receive several of each kind of nutrient to grow well. Once
the chips are distributed, give the students 15 seconds to
gather chips (without moving tbeir "roots"—their feet).
4. Have students return to tbeir seats. Wbich ones got
some of each kind of nutrient? Those trees have plenty of
nutrients for growth, and students should add a new fat ring
to their drawing. Did some trees not get any of a certain
nutrient? If so. they are lacking necessary resources, and
students should add a thin line to their drawing. Did some
trees get lois of a certain nutrient? This can also keep trees
SCIENCE ACTIVITIES
Tree Life. Year 3: Looking at the Effect of Water on Tree
Growth
5. Have each student pair up with a student next to them.
Give each pair a cup of water. In each pair, give one student
a short, thin straw and give the other a long, fat straw. The
straws represent the roots of a tree. Challenge them to drink
as much water as they can in a 5-second period. Then ask
students to raise their hands if they were able to drink lots
of water (should be those with long, fat straws); these
"trees" have received plenty of water for growth and should
add thick growth rings to their drawings. Those trees that
didn't get much water (students with short, thin straws)
would not have been able to grow as much: they should add
thin growth rings to their drawings.
6. After collecting cups and straws, discuss with students
what happened to their growth in the 3 "years" that were
simulated. What inhibited their growth? What helped them
to grow?
FOLLOW-UP SCIENCE ACTIVITIES
• Get tree cross-sections from different species of trees atid
compare the size of the rings. Which kinds of trees grow
faster? Slower? Trees that grow faster generally have softer
wood than those that grow slowly.
• Invite a forester (from the US Forest Service or a state or
local agency) to visit your classroom. Ask them to talk
about their work and to demonstrate how they use an
National Science Education Standards addressed in
these activltie.s:
Grade K to 4
Content Standard A:
Abilities necessary to do scientific inquiry:
Ask a question about objects, organisms, and events in
the environment.
Employ simple equipment and tools to gather data and
exlend the senses.
Conient Standard C:
The characteristics of organisms:
Organisms have basic needs. For example, animals need
air. v^ater, and food; plants require air, water, nutrients.
and light.
Organisms can survive only in environments In which
ihcir needs are met.
From: National Research C()uncil. 1996. National science educaiion slanciards.
Washington. tX": Natinnal Academy Press,
B
c 40.
c
s-scct
from growing well; these "trees" should add a thin ring to
their drawing.
Vol. 41, No. 3
35.
30.
o 25.
U
u 20.
ameter of'
20
0
^
^
^
-
^
^
10'
5
6
7
K
Age of Tree (years)
9
iO
FIGURE 5. Change in size of tree (diameter of trunk)
with age as measured by growth rings.
increment borer. They can also answer questions from the
class about how trees grow, how different tree species vary
in their growth requirements, and strategies for getting and
using resources.
• Explore different adaptations in trees for resource
competition. For example, waxy leaves help prevent water
loss so that the tree will not need as much water from the
soil. Deep tap roots allow trees to reach water that has
traveled deep into the soil. Canopies that spread wide allow
trees to get lots of sunlight, but growing tall instead means
they can grow past other trees that may shade them. Go
outside and look at trees in your neighborhood and see what
kinds of adaptations you can tlnd.
CROSS-CURRICULAR APPLICATIONS
Mathentatics: As discussed above, tree-ring investigations provide opportunities for students to create graphs
with real data. Your class can create bar graphs that describe
a number of trees of different ages (Figure 4) or that compare size of growth rings in trees of different species. If you
both count the age of the trees and measure the diameter,
you can create a line graph showing how trees change size
with age (Figure 5). As another math application, you can
have students measure the volume of water in their cup
before and after the water activity and determine through
subtraction how much water they drank.
Reading/Literatufe: There are a number of good books
about trees and their lives that you can share with your class
or have students read as part of their reading program. We
recommend a few for you in the bibliograpby below.
Writing: After going through the main activity above, ask
students to write a story pretending to be a tree, de.scribing
their life as a tree and things that affect the tree's growth.
Fall 2004
SCIENCE ACTIVITIES
This will reinforce the concepts from the lesson, give the
teacher an opportunity to assess student learning from the
lesson, and provide an opportunity for creative writing.
Bibliography:
Bash. B. 2002. Ancient ones: The world of ihe old-growth Douglas
fir. San Francisco, CA: Sierra Cluh Books.
-. 2002. Tree of life: The world of ihe African Baobcdj. San
Franeisco, CA: Sierra Club Books.
21
Blaekaby. S. 2003. The world's largest plants: A book about trees.
Mankato, MN: Pebble Books (Capstone Press).
DoiTos. A. 1997. A tree is growing, ^4ew York. NY: Scholastic Inc.
Dowd, J. 1992. Ring of tall trees. Portland. OR: Alaska Northwest
Books.
Kalman. B.. and K. Smithyman. 2002. Life cycle of a tree. New
York, NY: Crabtree Publishing.
Ring, S.. and L. Myott. 2003. From tree to table. Mankalo, MN:
Pebble Books (Capstone Press).
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