When measuring sample trees, which have co-dominant stems, for a linear regression table, the quotient frequently exceeds 1. I know that frequently trunk area / circumference can be greater at DBH than the measured stump height but is it appropriate to use in a LR table???
Thanks, James.

Reply to post by James Causton, on June 28, 2002 at 15:21:50:

I would guess it depends on two things. 1) whether you expect that the appraised tree was multiple stemmed and 2) how you would measure a multiple stemmed appraised tree that's still there to measure. Would you use DBH no matter what it is? Would you use some average of stems? Would you adjust to some number representative of single stem crown size?

Reply to post by Scott Cullen, on June 28, 2002 at 15:21:50:

Hi Scott,
. The trees I am dealing with are in one of two rows, luckily I have the luxury of similar trees right on site. Out of a total of 63 trees on the site 54 of them are co-dominants and there are 7 stumps cut 3 inches above ground. Out of 20 sample trees I planned on measuring 3 single stemmed trees.
I planned to measure cross sectional areas of all stems @DBH which were down to 50% of the largest stem, considering smaller than that to be a branch rather than a stem.
I was planning on using DBH throughout. Crown size does not vary between single stem and co-dominants. Would appreciate any comments on the planned approach,

Thanks, James

Reply to post by James Causton, on July 02, 2002 at 07:16:07:

James, I would be less concerned with trying to regress out a stem size that reprresents what the seven "stump" sizes would be if you had actual trunks at DBH given that 54/63 are likely to tbe multi-trunked, than I would try to come up with a DBH stem size that reprresents the functional loss. Do you think the typical multi-trunk number (adding them up? averaging them? how are you treating them?) will be greater or less than the typical single stem? You observed the crown sizes are the same. IF the multi-trunked # is higher it seems to me it will overstate function per sq.in. and if the # is lower it will understate. REmember cross sectional area is just a simple surrogate for a bundle of benefits provided.

Reply to post by Scott, on July 03, 2002 at 16:13:04:

The Guide explains this situation (Multi-Stem Tree, Method 3, p49). If the stems do not contribute their proportional share to the crown, the area of the stem can be weighted (depreciated) on a percentage to express it's share. The Guide gives an example for one way to do this, based on a factor of area and crown volume. This represents a direct adjustment to the XC area for suppressed stems.

Reply to post by James Causton, on June 28, 2002 at 15:21:50:

Strictly speaking, linear regression may not be best for what you are trying to do. The 'linear' part might be a problem, since trees probably seldom give a linear size correlation. As the trunk grows in diameter, the the root base (3 inches high) will probably increase at a faster rate, so there will be a curvilinear correlation.

An easier way for the simple problem is to plot your points on a graph, and visually graph the line. Not as accurate, but then the trees seldom study the math, either. Once you graph the standing trees, use the chart to determine where the fallen trees are, and use that DSH for your calculations.