CROWN ARCHITECTURE OF SHORT-ROTATION, INTENSIVELY CULTURED POPULUS .1. EFFECTS OF CLONE AND SPACING ON 1ST-ORDER BRANCH CHARACTERISTICS

First-order branch characteristics that have a major influence on crown architecture were quantified for nine 4 yr old Populus clones grown at 3 spacings (0.3 m .times. 0.3 m, 0.6 m .times. 0.6 m, 1.2 m .times. 1.2 m) under short-rotation, intensive culture (SRIC) in northern Wisconsin, USA. The branch characteristics included the number, length and diameter of branches and the angles of origin and termination. Clone and spacing had statistically significant effects on all branch characteristics, but the clone-spacing interaction was not significant for any branch characteristic. As spacing increased, the number, sum of lengths and angle of origin of branches increased, but the angle of termination decreased. Branch length and branch diameter were highly correlated within all clones. The correlation between the angles of origin and termination within a clone was low when pooled over all spacings and height grown increments. The 2 clones with the lowest angle of origin also had the lowest angle of termination, and the clone with the highest angle of origin had the highest angle of termination. The clonal rankings for angles of origin and termination were not otherwise similar. The results indicate that development of a biologically meaningful variable for effective branch angle may be a complex task for SRIC Populus. Individual clones are recommended for SRIC growth-spacing trials based upon branch angle and other crown architecture data presented.