How to weigh a tree

Calculating the CO₂ sequestered in a tree

Comparing the CO₂ produced by a family or school to the CO₂ sequestered in a tree.

Extension

How to weigh a tree 

Pick a tree at school or in the community that the students will see on a regular basis. When they see the tree they will think about the CO2 they are putting into the atmosphere. After you have picked a tree you need to identify its species. There are a number of fine identification keys available on the web (see "Resources").

Use a string and ruler to measure the circumference of your tree at chest height. If your tree is on a hill stand on the uphill side of the tree. Pace off a convenient distance from the tree (50 - 100 ft). Hold a ruler vertically at arms length. Line up the bottom of the ruler with the base of the tree. Using the ruler measure the apparent height of the tree. Measure the distance from your eye to the ruler. 

Put your measurements into either the JavaScript calculators or the Excel spreadsheet (see "Downloads") these give you the height and diameter of the tree. Determine if your tree is a pine tree, Yellow poplar, Sweetgum, Hard Hardwood, or Soft Hardwood tree. Put this information into the appropriate JavaScript calculator or the Excel spreadsheet to find the tree's green weight. These values are good for the Southeastern U.S. If you live in a different area you could improve the accuracy of your calculations by getting the local variables from your extension agent and putting them into the algorithm.  

Materials needed:

tree, string, ruler, tree identification key or book, calculator (pocket, JavaScript, or Excel), table of tree types (see "Resources")

How to calculate the CO₂ sequestered in a tree

First you need to remove the water from your tree. Find your tree's dry weight/green weight in the resources table. Entering that into the Excel spreadsheet will give you the dry weight, carbon and CO2 sequestered by your tree. If you are using the JavaScript calculators you need to multiply the dry weight by .5 to get the weight of the carbon in the tree. This is the above ground weight. The roots weight approximately 20% of the above ground weight. The total tree weighs 120% of the above ground weight. Multiply the carbon in the tree by 3.66409.

Materials needed:

calculator (pocket, JavaScript, or Excel), dry weight/green weight in the resources table

Comparing the CO₂ produced by a family or school to the  CO₂ sequestered in a tree

The average household drives 20,895 miles per year. Calculate the number of trees needed to sequester the CO2 produced by a family driving different kinds of cars. How much CO2 is produced by your school buses each month? How much CO2 is produced by teachers and students driving to school each month? How many trees is this equivalent to? 

On average electricity production in the U.S. produces 1.64 pounds of CO2/kWh. Find the number of kilowatt hours that the power plant can produce when it produces the amount of CO2 your tree has sequestered. Count the light bulbs in your class. Determine the kWh of electricity used by these lights each month. How many classes are there in your school? What is the electrical use of your school each month?  How many months worth of CO2 is sequestered in your tree?

Natural gas produces .12 pounds of CO2/ft3. Fuel oil produces 22.29 lbs of CO2/gal. How many pounds of CO₂  are produced to heat your school each month or for the winter months?  

How many trees worth of CO2 is your school responsible for producing each month? Each year? How much area does your tree take up? How much of the football field would you have to plant in trees each year to sequester the CO₂ your school produces?

Materials needed:
calculator (pocket or Excel), MPG for different vehicles (EPA is a good source see "Resources"), school's energy use (electrical, natural gas, heating oil, school bus fuel, check with principal and or central office).

Extension:  

Which tree weight did you use, above ground, roots, or total weight? Why did you pick that one over a different weight? The green weight includes the leaves. They fall off each year and turn back into CO₂. We don't have enough information to decide how to deal with these issues. The lesson ãForests, Mining Carbon from the Airä uses a professional model to explore carbon as it moves through a forest, its products and the atmosphere.

  Resources

These 2 EPA sites will lead you into hours of EPA material and calculators.

http://www.fueleconomy.gov/feg/findacar.htm 

http://www.epa.gov/globalwarming/tools/wc_assum.html

The Center for the Study of Carbon Dioxide and Global Change 

http://www.co2science.org/carbon/carbon.htm

These are tree identification keys available on line.

ID It Virginia Tech tree Identification Key using leaves and twigs

Identification of Common Trees of Iowa Iowa State University Extension Forestry, discussion of tree types and tree identification. 

Trees for the Pacific Northwest College of Forestry, Oregon State University

Upper Peninsula TREE IDENTIFICATION KEY from Michigan State University Extension

Basics of Tree ID Key to Leaves of Virginia Trees (for use with the 4-H tree identification project) by Dr. Jeff Kirwan and James Ward