Abstract: Elevation changes may affect intraspecific relationships or interspecific relationships among species. However, previous studies on Quercus variabilis have rarely investigated how its population interactions vary with elevation and how the factors affect them. Here, we examined the species relationships in Q. variabilis natural secondary forests across the three different elevation ranges (lower, medium, and higher elevation areas) using the niche and the Hegyi competition method. As the elevation increased, Q. variabilis strengthened its dominant position, and the overall association between populations shifted from positive to negative, as evidenced by a significant decrease in the positive-to-negative correlation ratio from 0.45 (85/191) to 0.41 (80/196) and then to 0.32 (29/91), indicating that the interspecific relationship gradually transitioned from facilitation to competition. The ratios of the intraspecific competition index to interspecific competition index were 3.09, 8.92 and 6.82, respectively, indicating that Q. variabilis forests had greater intraspecific competition compared to interspecific competition, especially in the medium elevation area. The intraspecific and interspecific competition in the lower and medium elevation areas showed a decreasing trend with the increase of diameter class, while the competition among individuals in the higher elevation area became more stable. The SEM showed that soil properties were indirectly negatively correlated with the species competition through a significant negative effect on forest density, while community characteristics only had a significant negative effect on intraspecific competition. Our results demonstrated that elevation factors decreased the intraspecific and interspecific relationships within Q. variabilis forests, providing new insights into the effective conservation of Q. variabilis natural forests.

Key words: Quercus variabilis, elevation, intraspecific association, interspecific and intraspecific competition, temperate secondary forests