Analysis of Early Growth Dynamics of the Third Generation Improved Varieties of Chinese Fir(Cunninghamia lanceolata)

This study compared the growth performance(tree height,breast height diameter,and individual standing timber volume) of four 3^rd generation Chinese fir varieties at 5 and 8 years after afforestation. Results showed that the survival rate of all tested varieties exceeded 84% during the 5th~ 8th year period,maintaining a high and stable level overall. Among them,Weimin 3^rd generation achieved the highest survival rate(98. 92%),while Youxi 3^rd generation had the lowest(84. 26%) . Significant differences were observed in the three growth traits across varieties:at 8 years,Weimin 3^rd generation and Jiangle 3^rd generationoutperformed Xipi 3^rd generation and Youxi 3^rd generation significantly. Their individual standing timber volumes were 30. 36% and 59. 17% higher than Xipi 3^rd generation,and 22. 46% and 49. 53% higher than Youxi 3^rd generation respectively. In terms of phenotypic coefficient of variation(CV),Weimin 3^rd generation exhibited the lowest CV for all traits(volume CV = 56. 32%),whereas Jiangle,Xipi and Youxi 3^rd generation had higher CV(74. 04%,82. 78% and 80. 59% for volume,respectively) . For growth dynamics,the average annual growth rates of tree height and DBH in the early stage(1st~ 5th year,V₁)were higher than those in the middle stage(5th~ 8th year, V 2),while the volume growth rate in V₂ was significantly higher. Overall,Weimin and Jiangle 3^rd generation maintained higher annual growth rates than the other two varieties,though the growth disparities in tree height and DBH among these varieties narrowed asthe stand age increased. All varieties remained in a steady growth stage. By comparison,the Weimin 3^rd generation superior variety and Jiangle 3^rd generation superior variety are more suitable for afforestation and promotion in the Youxi area. The relevant research results have analyzed the growth pattern of the 3^rd generation of Chinese fir,providing scientific reference for guiding the application of different 3^rd generation Chinese fir varieties in different regions.