Abstract: Quantitatively describing forest structural diversity is the foundation and key to the dynamic regulation of forest structure and the precise improvement of forest quality. Quercus aliena var. acuteserrata secondary forest was surveyed in four periods (2008, 2013, 2018 and 2023). The bivariate distributions of diameter at breast height (DBH) class and spatial structure parameter were used to quantify structure dynamics. The differences of size differentiation and spatial structure among these periods were quantified. The results showed that DBH class distributions of trees were well mixed, and that spatial distribution patterns or dominance degrees were significantly different at different periods (P<0.05). Tree size was positively correlated with dominance status across different periods. The diversity of tree size structure was relatively poor and exhibited slight temporal fluctuations. The forest spatial heterogeneity generally showed a slight inverted U-shaped trend, but the spatial diversity tended to be favorable. Therefore, tree size differentiation in Q. aliena var. acuteserrata secondary forest was pronounced under different spatial structures. Both tree size and spatial structure diversity exhibited a certain degree of volatility. It is suggested that management techniques and measures targeting the distribution pattern and competitive micro-environment should be prioritized to provide references for dynamic optimization of forest structure and precise improvement of forest quality.

Key words: spatial structure, size structure, community dynamic, bivariate distribution, structural diversity