Assessments of growth performance, crown structure, stem form and wood property of introduced poplar clones: Results from a long-term field experiment at a lowland site

Abstract

Climate change brings about more frequent short-term waterlogging leading to unfavorable conditions for tree growth. Poplar is a preferred tree species for fast-growing plantations. Although limited short-term comparative studies exist with poplars that examine clonal variation in growth and physiological responses to waterlogging, a comprehensive assessment on growth performance, crown structure and wood property of poplar clones is lacking from a long-term study. This study compares the clonal variations in survival rate, growth, crown structure, stem form and wood property of poplar clones to better match the genotype with specific site. In line with the result of the preliminary evaluation, 17 poplar clones were harvested to further investigate crown structure, stem form and wood property after 24 growing seasons. A significant difference in tree growth was observed among the clones, ranging from 1.08 to 2.64 m3 for tree volume, whereas male clones generally had a better growth performance than the female. Hierarchical cluster analysis indicated the 17 poplar clones can be classified into three distinct groups in term of mean values of branching angle, branch numbers and branch base diameter. There existed visible differences in breast-height form factor and height-diameter ratio among the poplar clones, and four distinct groups can be divided based on Euclidean distance of stem form indexes. Significant clonal variations in wood basic density (WD) and microfibril angle (MFA) were observed among the sampled clones, and the mean clonal WD and MFA at breast height ranged from 0.325 to 0.390 g/cm3 and 11.8 to 16.7° respectively. Based on the TOPSIS method, a comprehensive assessment of adaptability and prioritization of the 17 clones was made from tree volume growth, stem form, branching traits and wood density, and some superior poplar clones were recommended for future applications in the similar lowland sites.