Crown architecture of Populus clones as determined by branch orientation and branch characteristics.

Crown architecture, including branching pattern, branch characteristics and orientation of proleptic and sylleptic branches was studied in five poplar clones (Populus deltoides, P. trichocarpa and P. trichocarpa x P. deltoides hybrids), grown under intensive culture in the Pacific Northwest, USA. Branch characteristics measured were number, length, diameter, biomass and the angles of origin and termination. The results suggest that genotype has a major influence on crown architecture in Populus. Clonal differences in branch characteristics and branching patterns were found that resulted in striking differences in crown form and architecture. Branch angle and curvature differed significantly among clones, and among height growth increments within clones. Branch length and diameter were significantly correlated in all clones. Sylleptic branches and the considerable leaf area they carry have important implications for whole tree light interception, and thus, play a critical role in the superior growth and productivity of certain hybrid poplar clones. The considerable variation in branch characteristics implies a strong justification for including them in selection and breeding programs for Populus.