What more can I learn from my tree?

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 in them.

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 the tree is cut down, the wood dries out. Green weight is the weight of the tree when it is alive. 

Our bodies are mostly water. The average adult human body is about 50 to 65 percent water. A child’s body is closer to 75 percent water.   We have different body types. Some of us have more muscle, others more fat. Some people look like they are mostly skin and bones. That is why the percentage of water can vary so much. Trees also 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.

The percentage of water in trees also varies. A tree can be more than one-half water. 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.

To find the dry weight of your tree, multiply its green weight by the dry/green ratio.

You can use your calculator or our online dry weight calculator.  

Once again you have an answer. Really we have a whole table full of answers. Using the table find a relationship between the dry weight of a tree and its percentage of water.

Chemicals in trees

Trees are 50% to 53% cellulose. 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.

Minerals make up 1% of trees. 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. Find the weight of carbon in your tree by multiplying the tree’s dry weight by .5.

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.

Need help?  

Cars produce CO₂ by burning gasoline. For each gallon of gasoline burned 20 pounds of CO₂ is 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.

People produce CO₂ in a variety of ways. Next we will explore several of these carbon pathways.

Now that you understand the algorithm, you can put all of these calculations together in a computer model. Then you can explore the relationship of human production of CO₂ and trees' ability to sequester it. The computer will do your calculations.

Find the miles per gallon for several cars, trucks and motorcycles. 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 vehicles.

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

On average, electricity production in the US creates 1.64 pounds of CO₂/kilowatt hours (kWh). Find the number of kilowatt hours that a power plant can generate 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 is your tree equivalent to? How many kilowatt hours of electricity do the lights in your classroom consume in a day, week, month, year? How many kilowatt hours of electricity does your school consume in a month, year? How many trees is this equivalent to?

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 it is, how many trees would be needed to sequester this CO₂.

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? 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? How can we evaluate a tree’s or forest’s long term ability to counteract the CO₂ we are putting into the air?

The module “Forests, Mining Carbon from the Air” will help you explore these issues.