3.1. Population structure and its temporal change
We found 144 individuals of Q. chungii with DBH \(\geq\)1 cm and 37 individuals with DBH \(<\) 1 cm within 3800 m2 in 2023. Only one of the seedlings with DBH \(<\) 1 cm was produced from seed, while the others were sprouted from roots of established trees. The overall population density was about 4.76 individuals per 100 m2.
The population structure in 2023 showed a pyramidal structure (Fig. 1). The focal species could produce a large number of germinated seeds (age class 1), but the number of seedlings (age class 2) dramatically decreased, suggesting high risks of death from stages of seed to seedling. The pattern is similar from stages of seedling to sapling (age class 3). The numbers of medium trees at age classes 4–5 were larger than those of saplings and large trees (age classes 6–7).
In the past decade of 2013–2023, both the abundance and frequency ofQ. chungii increased, suggesting active regeneration processes (Fig. 2). The basal area also increased in this decade (Fig. 2). For individuals with DBH\(\ \geq\) 2.5 cm (age classes 3–7) surveyed in both years, the proportion of saplings decreased from 2013 to 2023, while the proportions of trees with larger sizes (age classes 5–7) increased through time (Fig. 3), suggesting substantial growth in the past decade.