This site is for people who like plants -- growers, enthusiasts, aesthetes, novices and professionals, those who appreciate wild things and those who appreciate the cultivated. I garden in Chelsea, and I've been visiting people's yards for 20+ years in the course of my work. My goal is to make this blog a community project, so if you share my interests, please consider becoming a participant and contributing content -- Guerin. Info:

Thursday, January 20, 2011

First entry for the NEW Ann Arbor Big Tree Registry

The city used to maintain a registry of big trees --that is until the forestry office was moved away from West Washington Street. Nobody seems to have kept a record of the list. So I'm starting a new one. My first candidate is:

Kentucky coffeetree (Gymnocladus dioicus), 1205 Wright St: 105' height, 43" diameter, 63' average crown spread. Total:  246 points of 'big-tree-ness.'

And before you all get all hot and bothered, yes I intend to include the big chinkapin oak in Wurster Park seeing as it is the state champion. I just have to get over there and measure it.

If you want to join the fun, send in your candidates. You can even do the measurements yourself. Here's how: 

Diameter is measured at 4.5' from the ground.

Estimating height is a little more involved: first, measure a distance (say, 100') from the tree. Then, using a clinometer (an i-Touch or i-Phone with a 99 cent application works fine), record the angle when you point to the center of the top of the tree, then record the angle when you point to the bottom of the tree (note: this is likely to be a negative number); the final number you want to use is the difference between these two angles. Now a little math. Take out a scientific calculator (standard on an i-Touch) and compute the tangent of that final number. That number divided by the distance from the tree equals tree height (more or less). If you get confused, sketch in out on paper and recall that the tangent of an angle in a right triangle equals the ratio of the opposite side to the adjacent side.

Finally crown spread is determined most easily on a sunny day by measuring the shadow cast by the crown. Do this in two directions, perpendicular to each other, and take the average. On a cloudy day, just do your best by looking up and measuring from the drip-line.

Big tree points are determined by the formula: height (in feet) + circumference (in inches) + 1/4 average crown spread (in feet).

1 comment:

  1. Of course you know there are two 'Big Trees' at Wurster.

    Other I am sure you know about, but are among my favorites: the large oak at Mushroom Park, and the guy hiding back off the boardwalk at Parker Mill Park.