## Friday, May 9, 2014

### A Poem As Useful As a Tree

I wish everyone could enjoy the beauty of trees as much as I do. Each one is a better poem than anything written by a human. Even ugly trees (and there are a few) are interesting. But if someone just thinks trees are useful, I’ll settle for that.

I had my botany students do an exercise in trigonometry, in which they measured a tree (each group had its own tree) and estimate the number of twigs on the tree. The results were astonishing. It is not unusual for a big oak tree to have 50,000 twigs.

Then I had them estimate their own carbon footprints, using websites that do the calculations. A typical number would be 50,000 kg of carbon dioxide per year from their activities.

Next I had them do some simple arithmetic. Just some multiplying and dividing. I had them assume (from actual measurements made in previous years) that each twig had 100 square cm of leaf area. This would mean a typical tree had 5,000,000 square cm of leaf area, which is 500 square m (they had trouble with this). If you assume (also based on measurements in previous years) that a typical tree absorbed 10 grams per square meter per day of carbon dioxide, this would be 5,000 grams or 5 kg of carbon dioxide per day. This may seem low to you, but remember these are post oaks in a dry forest. This means that it would take their tree 10,000 days to absorb 50,000 kg of carbon dioxide. Assume a growing season is 180 days. It would take the tree over 55 years to absorb that much carbon dioxide.

Which means there has to be 55 mature oak trees to compensate for one person’s carbon emissions.