Twenty-five-year response of Larix occidentalis stem form to five stand density regimes in the Blue Mountains of eastern Oregon

by Lennette, Andrew P.

Upper-stem diameter measurements from a levels-of-growing-stock study on Larix

occidentalis in the Blue Mountains of eastern Oregon were collected over a 25 year period

with an optical dendrometer. The following hypotheses were tested with these data: 1)

stand density regime has a significant effect on stem form; and 2) crown size controls the

response of stand density regime to stem form. The five stand density regimes

corresponded to five different growing-stock levels (GSLs) defined by bole surface area.

A variable exponent taper model was fit to the data from each individual tree and the

resulting parameters were treated as indices of stem form for comparisons among density

regimes. MANOVA performed on these parameters estimates confirmed statistically

significant differences in stem form both between the two lowest levels-of-growing stock

and between these two treatments and all three regimes with higher levels of growing

stock. The individual tree parameter estimates were also tested in the context of a

seemingly-unrelated regression (SUR) analysis. The two stem profile parameter estimates

were closely related to diameter! height ratio and crown ratio, respectively. Indicator

variables for the different density regimes did not contribute any explanatory power

beyond diameter/height ratio for the first parameter or crown ratio for the second

parameter. DBH, height and crown ratio are concluded to account for the variation in stem

form imposed by differences in stand density management.