Radial Growth Rate   Edward Frank
  Mar 05, 2007 18:37 PST 

I will elaborate of the discussion of the how to determine radial growth per year. As an aside, in math class there were always two phrases that bothered me. When the instructors would get to a critical point in the problem they would come up with: "it is intuitively obvious that" Perhaps it was obvious to people with advanced degrees in mathematics but it wasn't to the many of the people, myself included taking the introductory courses. The second phrase was "I have changed notation here in order to simplify the problem" I had just figured out the old notation, now they were changing to something completely different. It in no way did this simplify the problem for me. I think oft times they were trying to demonstrate they were smarter than everyone else. That is proposition I highly doubt. So when I try to explain how to do something, I include even the most basic steps. It is not to denigrate anyone's intelligence, but to avoid the "intuitively obvious" trap.

First if you have a circumference in feet and inches, it must be converted to a uniform type of unit. You can do this by either changing all of the figures from feet and inches to just inches. The other way is to convert the inches to decimal feet. Fractions of an inch must be converted to decimals: 1/4" = 0.25", 1/2" = 0.5", 3/4' = 0.75" and so forth whichever option you choose to use.

To convert to decimal feet divide the number of inches by twelve and add it to the number of feet. There is no need to do any decimals beyond two places, because the measurements just aren't that accurate. In Larry's example the original cbh (circumference breast height) was 14' 7". That is 175 inches or 14.58 feet.    The ending circumference is 23 feet or 276 inches.

For this purpose I will work with inches of circumference. The formula for the circumference (or cbh) and radius relationship is:
         cbh = 2(pi)radius    with pi = 3.1415, therefore: radius = cbh/ 2(pi); or   radius = cbh / 6.283

So if you want to calculate the change in radius, change = 276 / 6.283 - 175 / 6.283 ,   change = 43.93 - 27.85 = 16.08 inches

This can be done in a simpler way by combining the calculations to get:   (end cbh - start cbh) / 6.283; in this case the numbers work out to be (276 - 175) / 6.283 = 101 / 6.283 = 16.08 inches.

To determine the rate of growth divide the change in radius by the number of years.

In this example: growth rate = 16.08 inches / 73 years = 0.22 inches per year. It is likely the number of the years is closer to 72 than 73, so that the growth rate is closer to 0.223  It is reasonable to use three decimal places in this final calculation.

Edward Frank

    -------------- Original message --------------
    From: tuce-@msn.com

    > The Friendship Oak,is located at University of Southern Ms., in Long
    > Beach. The tree was measured and registered with the Live Oak Society in
    > 1934, CBH-14'7". In 2007 it measured CBH-23' a 9'7" difference. We have
    > the Ruskin Oak growth rates and we have the Friendship Oak growth rates
    > for this 73 year period! The Ruskin Oak grows on a small hillside, while
    > the Friendship Oak grows near the beach. It had about 15' of water under
    > it during Hurricane Katrina in 2006 and about the same from Hurricane
    > Camille in 1969. I'm sure it has been under several more times in its
    > 300-400 year life! My point is one tree has not been flooded with
    > saltwater, while the other has.