Niche and interspecific association of dominant arbor species in Quercus communities in the Qinling Mountains, China

Study of niche characteristics, species interactions and community connectivity along elevation gradients contributes to our understandings on species' spatial interactions and vicarious distribution pattern, and helps reveal congeneric species coexistence and formation mechanisms of species distribution boundaries. In this study, we conducted a field survey on five types of Quercus communities across six elevation belts ranging from 900 to 2300 m (a.s.l) on the north and south slopes of Qinling Mountains, where the north subtropical and warm temperate zones divide. We analyzed the importance values, niche widths, niche overlaps, competition, interspecific associations of the three dominant Quercus species, as well as community connectivity. The richness of tree layer in the vicarious distribution of Quercus communities was relatively low, with Pinus (Pinus armandii and Pinus tabuliformis) being the main associate species. The χ² test and Spearman analysis demonstrated a significant negative correlation between Pinus and Quercus. The nich widths of all three studied Quercus species were found to be wider in their core communities compared to their edge communities, pariticularly on the south slopes. The niche overlap of dominant species on the both slopes were at a relatively low level, while higher niche overlap observed on the north slopes compared to the south slopes. The elevation trend in niche overlap among dominant species was consistent with interspecific competition intensity. Compared to the core and upper edge areas, the Quercus communities in the lower edge area exhibited greater niche overlap and a higher proportion of interspecific competition. The resutlts of variance ratio (VR) and W statistic values indicated that the Quercus communities on the both slopes primarily exhibited a non-significant negative correlation. The associations among dominant species were weak, resulting in a relatively loose community structure. Overall, the communities were in a relatively stable stage of middle-late succession. For the conservation and restoration process of Quercus forests, appropriate artificial interventions should be implemented to adjust interspecific relationships and enhance the strength of interspecific connections.