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Dear Editor,

In 1999, I published an article, "Tree Measurements: An Outdoor Activity for Learning the Principles of Scaling," in The American Biology Teacher, 61(9), 677-679. This article described a project in which students measure the diameters of tree trunks, and use trigonometry to estimate tree heights, then use these measurements to explore the principles of allometry that apply to plants, animals, and even to buildings.

I would like to suggest a couple of changes that will make this project a little easier to do. In the article I suggested that the students pool together their data to make a scatterplot with tree height as one axis, and trunk diameter as the other. A positive correlation is inevitable, therefore I suggested choosing two tree heights that differ by a factor of two, and comparing their trunk diameters, which should differ by a factor greater than two. This procedure works, but the scatterplot does not provide an easily visible confirmation confirmation of the hypothesis. My students would frequently get lost during these calculations.

Instead, I have begun to have the students calculate a height-to-trunk-diameter ratio for each tree. If trunk diameter increases relatively more than height as the tree grows, then the height-to-diameter ratio should decrease during growth. In a recent laboratory activity, my students performed performed these calculations on nine trees. The scatterplot (see accompanying figure) shows a clear decrease in height-to-diameter ratio, which confirms the hypothesis at a single glance.

I hope that this modification will make the project easier.

Stanley Rice

Associate Professor

Southeastern Oklahoma State University

Durant, OK 74701
Height-to-trunk
diameter data
for nine trees.

23.5 0.289
 66 0.22
 70 0.184
15.5 0.42
79.5 0.19
28.3 0.44
27.7 0.42
73.2 0.193
47.8 0.324
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Article Details
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Author:Rice, Stanley
Publication:The American Biology Teacher
Article Type:Letter to the editor
Date:Apr 1, 2007
Words:303
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