Carbon Sequestering in Trees
Planting trees, which are a carbon reservoir, is one proposed method of carbon sequestration. Photo courtesy of McD22/Flickr.
In burning fossil fuels as an energy source, we are taking stored carbon and putting it back into the atmosphere at a rate that is greater than it is being taken out. This causes means that the amount of carbon dioxide in the atmosphere is increasing, and will continue to do so until the difference in these two rates disappears. One way to bring this about would be to greatly curtail the rate at which we burn fossil fuels. Many people do not like this idea, as it would mean a great change in our lifestyle. Another proposed method would be to speed up the rate at which carbon is removed from the atmosphere. One way of doing this would be to plant more trees.
During photosynthesis, trees convert carbon dioxide and water into sugar molecules and oxygen. The overall equation looks like this:
6 CO2 + 6 H2O + sunlight ---> C6H12O6 + 6 O2
Some of this sugar is stored, while most of it gets used by the tree for other purposes such as energy and structure. For instance, a great deal of the sugar is linked together to form cellulose, which provides the structure for the tree.
If we look at this sugar from a mass standpoint, we see that a large fraction of it is due to the carbon. Taking into account the other types of molecules that are found in a tree (proteins, lipids, etc.), approximately 45% of the dry mass (not including the water) of a tree comes just from carbon. In other words, a 100 kilogram log of a tree that has been completely dried contains about 45 kilograms of stored carbon.
While each kilogram of dried tree is storing .45 kilograms of carbon, it is removing more than a kilogram of carbon dioxide from the atmosphere. This is because each carbon dioxide molecule contains two oxygen atoms.
This large of an amount gives the idea of using trees to remove carbon from the atmosphere a lot of validity. However, it should also be pointed out that this equation works in reverse. When a tree is burned or allowed to decay completely, the carbon in the tree is put back into the atmosphere as carbon dioxide. Worldwide, we are actually losing forest, and this relationship shows why we should be concerned.
Source: ESA21. Trees and Carbon. Retrieved from http://esa21.kennesaw.edu/activities/trees-carbon/trees-carbon.pdf on October 13, 2010.
Last modified: Monday, 5 March 2012, 11:30 AM