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You have found the answer!! You have an estimated green weight for your tree. Answers are nice but the nice feeling only lasts a little while. The real excitement is in the exploration and discovery. Scientists want to jump right back into the science so they won't get bored. The scientists look at their answer and try to find new questions to explore.
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Can we find any questions in our tree's green weight? First what does green weight mean?
When trees are alive, their cells like yours, have water in them. When a tree is cut down, the wood dries out. Green weight is the weight of the tree when it is alive.
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Trees vary a lot between species. Some trees are tall and thin like many pine trees. Other trees develop broad crowns like oaks. After you get to know a type of tree, you can often identify them from a distance by their shape. You can probably do the same thing with your human friends.
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The percentage of water in trees also varies. A tree can be more than one half water by weight. Scientists have measured the green and dry weight of many different kinds of trees. The dry/green weight table gives the moisture content for different kinds of trees.
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To find the dry weight of your tree, multiply its green weight by the dry/green ratio.
You can use your calculator or our this online dry weight calculator.
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Once again you have an answer. Really, we have a whole table full of answers. Answers give us opportunities to ask more questions.
Is there a relationship between the dry weight of a tree and its percentage of water?
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You have found the dry weight of your tree. Your tree is made of chemicals so we can ask:
What are the chemicals in your tree?
How many pounds of each of these chemicals are in your tree?
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Trees are 50% to 53% cellulose (dry weight). Cellulose is a polymer of sugar. Many sugar molecules are stuck together in a network to form cellulose. Animals can't break the cellulose down into sugar again. Some bacteria can break down cellulose. Cows and termites have these bacteria in their digestive systems. That is why cows can eat grass or even paper. Another 1% is minerals. The minerals are the ash you have after you burn wood. The minerals are elements like calcium and iron. The rest of the tree is lignin and some cytoplasm chemicals. Lignin is a group of protein chemicals that act like glue to help hold the cell wall together. When chemists analyze wood they find that 50% of a tree's dry weight is carbon.
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Find the weight of carbon in your tree by multiplying the tree's dry weight by .5.
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Knowing the weight of the carbon in your tree lets you can ask, where did this carbon come from? The tree got its carbon from CO2 in the air. We can ask how much CO2 has the tree sequestered from the atmosphere?
Find the weight of CO2 that your tree has sequestered.
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Cars produce CO2 by burning gasoline. For each gallon of gasoline burned, 20 pounds of CO2 are produced. When cars burn gasoline, they put CO2 into the air. When trees grow, they take CO2 out of the air.
Calculate how many gallons of gasoline the carbon in your tree is equivalent to.
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Find the miles per gallon for several cars, motorcycles, trucks. The average household drives 20,895 miles per year. Calculate the number of trees needed to sequester the CO2 produced by a family using these different kinds of transportation.
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On average, electricity production in the US produces 1.64 pounds of CO2/kilowatt hour.
Find the number of kilowatt hours that a power plant produces when it produces the CO2 your tree has sequestered. Compare this to the number of kilowatt hours your family uses in a month. How many months of electricity used by your family is equivalent to the carbon in your tree?
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How many kilowatt hours of electricity do the lights in your classroom consume in a day, week, month, year?
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How many kilowatt hours of electricity does your school consume in a month, or year? How many trees are equivalent to the electricity consumed by your school?
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Natural gas produces .12 pounds of CO2/ft3. Fuel oil produces 22.29 lbs of CO2/gal.
Is your home or school heated with natural gas or fuel oil? If either is heated with natural gas or fuel oil, how many trees would be needed to sequester this CO2?
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We have calculated three different weights for your tree: the weight above the ground, the weight of the roots, and the total weight to the tree.
Which of these should we use when we consider the tree's contribution to our air?
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Every year your tree absorbs carbon to make its trunk larger and also to make new leaves. The carbon stays in the trunk. The carbon in the leaves returns to the air when the leaves rot the next year. Eventually, your tree will die or get cut down. What will happen to its carbon then?
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How can we evaluate a tree's or forest's long term ability to counteract the CO2 we are putting into the air?
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The module "Forests, Mining Carbon from the Air" will help you explore these issues.
