Climate Education Guide, Activity 3: Trees and Carbon
Forests store more carbon than any other land-based ecosystem. Tropical rainforests -- like Guatemala’s Petén region -- have the potential to store even more. In this activity, students will measure a tree to estimate the amount of carbon stored in it.
- Students will explain how to measure a tree’s height and diameter.
- Students will understand that taller and larger trees store more carbon.
As trees grow, they absorb carbon dioxide from the atmosphere and store the carbon in their trunks, branches and roots. Because they store more carbon than they release, forests are known as a carbon “sink.”
Forests are among the world's most important carbon sinks. They store some 289 million metric tons (tonnes) of carbon in the trees and plants alone. The total carbon stored in forests -- including the trees, plants, deadwood, litter, and soil -- is more than all the carbon in the atmosphere.(See Source A Below) Forests store more carbon than any other land-based ecosystem, and more carbon than all of the world’s remaining oil stocks.(See Source B Below)
By storing carbon, forests slow the rate that carbon dioxide accumulates in the atmosphere. One way people hope to reduce or reverse the build-up of CO2 in the Earth’s atmosphere -- and global climate change -- is to increase the amount of carbon stored in forests.
In tropical rainforests like the Petén, trees grow more rapidly than in other types of forests. These forests lock in as much as 15 metric tons (tonnes) of carbon per hectare per year.(See Source C Below) Planting trees in tropical rainforests can remove large amounts of CO2 from the air within a relatively short time.
The amount of carbon an individual tree can store depends on the species of tree, how large it is, and how old it is. In general, though, the larger the tree the more carbon it can store. Also, the faster growing the tree, the more quickly it will add carbon to its stores.
Source A: http://www.fao.org/news/story/en/item/40893/icode/
Source B: http://www.fao.org/forestry/52980/es/
Source C: “Forests and climate change: Better forest management has key role to play in dealing with climate change.” FAO Newsroom. http://www.fao.org/newsroom/en/focus/2006/1000247/index.html
- Student notebooks
- Ruler and large ball of string; or measuring tape
- Ruler or stick for each pair of students
- Student Resource Pages
Preparation: 20 minutes
Activity: One or two 50-minutes periods
Before doing the activity, select one or more trees for students to measure.
Doing the Activity
Remind students of the carbon cycle in Activity 2, and ask:
- Where in the carbon cycle is carbon stored? (Tree and wood product)
- How much carbon do you think might be stored in a single tree?
- Do you think bigger trees store more or less carbon than smaller trees? Why do you think so?
- Explain that since forests contain lots of trees, they are one of the world’s biggest stores of carbon. Students will learn how to measure a tree, and then use that information to find out how much carbon is stored in it.
- Take students outside to measure the tree or trees you have chosen. Have students bring their notebooks for recording the measurements.
- Ask students to estimate the circumference of the tree (how big around it is) in centimeters, recording their estimates in their notebooks.
- Point out that foresters always measure the width of a tree at 1.4 meters above the ground. (They call these measurements Diameter at Breast Height [DBH] or Circumference at Breast Height [CBH].) To see why this is an important standard, help students measure the tree’s circumference using a piece of string and ruler, or a tape measure, at 0.5 meter, 1 meter, and 2 meters from the ground. Ask students what would happen if everyone measured at different heights of the tree. (Everyone would get different results.)
- Help students measure the circumference at 1.4 meters, recording their measurements in their notebooks (see the Sample Data Sheet for Recording Tree Measurements [PDF]). Ask students to compare their actual measurements to their estimates.
Divide the class into pairs, and ask each pair to calculate the height of the tree using the following method:
Source: Activity 67: How Big Is Your Tree? Project Learning Tree PreK-8 Guide
- Student A stands at the base of the tree.
- Student B holds a ruler or pencil at arm’s length a distance away from the tree.
- Student B lines up the top of the bottom of the ruler or pencil with Student A’s feet, and places a thumb on it to mark the place where it lines with Student B’s head. This length represents the scaled height of Student A.
- Student B moves the ruler or pencil to see how many scaled heights of Student A it takes to reach the top of the tree.
- Student B measures Student A’s actual height and multiplies it by the previous result. For example, if the Student A’s height is 140 cm and it takes 6 scaled heights to reach the top of the tree, then the height of the tree would be 140 cm x 6 = 8.4 m.
- Students may record their measurements in their notebooks using the “Sample Data Sheet for Recording Tree Measurements” Have pairs compare their calculations for the tree height. How similar are they? What might explain any differences?
- Help students use the “How Much Carbon Is in a Tree?” [PDF] student page to determine the approximate amount of carbon stored in the tree.
Ask the class to think about how their tree compares to others:
- How does this tree measure up to other trees in the area?
- Does it have more or less carbon?
- Looking at the chart on the student page, which dimension--height or circumference--has a greater affect on the amount of carbon in the tree? (Using the chart, compare your tree to trees that are the same circumference, but taller; and the same height, but wider.)
- How might the trees in this forest compare to trees in other forests around the world?
- Help students use a field guide to identify the species of the tree you measured. In general, how does this tree species compare in size to other trees described in the guide?
- Find out how forest workers in your community measure trees and what they use the tree measurements for.
The Rainforest Alliance curriculum is unique in that it teaches science, math, language arts and social studies essentials while addressing the United States National Standards for Learning.
Science, Math, Social Studies
Observing, Comparing and Contrasting, Analyzing, Translating
From PLT Conceptual Framework:
- Organisms are interdependent, and depend on nonliving components of the Earth. (2.1)
- Populations of organisms exhibit variations in size and structure as a result of their adaptation to their habitats. (4.1)
- Our increasing knowledge of the Earth’s ecosystems influences strategies used for resource management and environmental stewardship. (5.5)
Evaluate the students’ understanding by having them write a paragraph or draw a diagram explaining how to measuring a tree to find out the amount of carbon in it.