Each annual ring width (ARW) was measured on the breast height stem disks for all the trees sampled.
The interaction leads to less effect of WH on KD with increasing site index given the same ARW. When the interaction between mean annual ring width at breast height ([ARW.sub.mean]) and WH was removed from the model, the parameter estimate for the interaction effect between [SI.sub.50] and WH became positive (model not presented).
This reveals that ARW patterns at breast height may be used to predict the knot structure within single trees without knowing the stand history, that is, without explicitly including treatment variables.
The differences in averages and coefficients of variation of ARWs, densities, and [E.sub.f] values among specimens with varying gauge lengths within a grade were small, as shown in Table 1.
The dimensions, annual ring width (ARW), density, and [E.sub.f] were measured for each specimen.