Effect of standing density and crown structure on standing volume of Cunninghamia lanceolata plantation

Cunninghamia lanceolata is an important plantation tree species in subtropical China, and the decline of stand productivity caused by its intensive management mode needs to be solved urgently. The objectives of this study were to explore the effect of Cunninghamia lanceolata crown structure on standing tree volume under different stand densities, so as to provide a theoretical basis for increasing the yield of Cunninghamia lanceolata plantation forests.

123 Cunninghamia lanceolata plantations in six provinces and autonomous regions (Yunnan, Guizhou, Guangxi, Hunan, Jiangxi and Fujian) were selected as the research objects. Firstly, Spearman's correlation analysis was used to explore the relationship between crown structural parameters, standing density and standing tree volume. The density was divided into three grades (0-1 200 trees/hm², 1 201-2 400 trees/hm², 2 401-3 600 trees/hm²), and then the relationship between crown characteristic parameters and standing tree volume under different densities was studied by difference analysis. Finally, subgroup analysis was used to analyze the interaction between density and crown structural parameters on standing tree volume.

The results showed that the crown volume, crown width, crown length, crown shape ratio and standing volume showed a very significant positive correlation (P<0.01), with the correlations ranging from strongest to weakest: crown volume > crown length > crown width > crown shape radio > crown radio; while the density showed a very significant negative correlation with the crown structure and standing tree volume; At different density levels, there were significant differences in standing volume, crown volume, crown width, crown length and crown shape radio (P<0.01); The interaction between density and crown volume, crown length, crown ratio, has a significant positive impact on standing tree volume (P<0.05).

Stand density has a significant negative impact on the standing volume and crown structure, and the accumulation of standing volume is affected by the interaction between density and crown structure, which provides scientific guidance for the adjustment of crown structure of Cunninghamia lanceolata plantations under different densities.