Direct and indirect effects of Poplar different attributes on its yield in early growth stage

Direct selection of poplar clones for expanding their plantation is based on yield (wood production) evaluation. Because of limitations in site ecological characteristics which prevent desirable production, this method is not applicable. Therefore, indirect selection by studying other phenotypical characteristics which have well correlation with yield could be useful. The Path test for some of the morphological and growth factors was tested on one to two year old poplar clones seedlings in 2000 and 2001. At each experimental unit, five seedlings were selected to measure their following characteristics. Leaf number, leaf area, total leaf area, length of blade, maximum leaf width, width/length ratio, petiole length, depth of leaf rib, vein number, branch number, branch length, branch diameter, stem diameter, stem diameter/branch diameter, branch angle, height, root number, root length, new leaf number and survival. After a confident result of differences between the species and their clones, for the characters, Path analysis was performed on the data.
The results showed that branch number and branch angle had great direct effects on height as an independent variable. Branch number affected the height directly and negatively at high level, but its indirect effect on height through the dependent variables, was positive. As a result, the total effect on height was negative (-0.554).
Leaf number left high positive effect on height. The branch diameter/stem diameter ratio had the greatest total negative effect on height. As a result, stem diameter had the greatest positive effect on height. Survival had also a great indirect positive effect on height through independent variables, counterbalancing negative direct effects to a positive effect of 0.667. Branch length showed a high negative direct effect, but a high positive indirect effect, resulting a high positive total effect on dependent variable, height. However, total leaf area with positive direct and indirect effects on height, which is in turn the most influential character on height, would be the best indicator of height in the poplar species under study. This would be of high value, particularly when a great number of clones are under investigation at early stages of a cultivation programme.