Niche and Interspecific Association of Dominant Tree Species in Spruce–Fir Mixed Forests in Northeast China

Abstract

This study focuses on the natural coniferous and broad-leaved mixed forest dominated by Picea asperata and Abies fabri in the Jingouling Forest Farm of Northeast China. Specifically, we place emphasis on examining the effects of different thinning intensities. By comparing the niche characteristics and interspecific associations of dominant tree species under various thinning intensity conditions, our aim is to gain deeper insights into the patterns of resource utilization by species and the interplay of tree species in the forest canopy. Based on plot survey data, analysis methods such as niche breadth, niche overlap index, Pearson correlation coefficient, and Spearman’s rank correlation coefficient were used to analyze the niche and interspecific relationship characteristics of the dominant tree species in the community. The results indicate that among the four selective cutting intensities, the tree species with the highest importance value in all cases is Abies fabri, with an average importance value of 30.29%. Additionally, Picea asperata exhibits the widest niche breadth among the tree species, with a value of 4.59. The selective thinning in this study resulted in a reduction of average species niche overlap in the community compared to the control plots. There were both positive and negative interspecies associations observed, but they were statistically insignificant. Few pairs showed significant correlations, with the positive-to-negative ratio of Pearson coefficients decreasing as the selective cutting intensity increased. The Spearman rank correlation analysis revealed a positive-to-negative ratio exceeding one for species pairs in the community under both light and heavy-cutting conditions, with no significant negative correlations observed. In summary, selective cutting disturbance can effectively increase the importance value of the dominant tree species, Abies fabri, in the community. However, it leads to a reduction in the niche breadth of all tree species present in the forest. Moderate selective cutting is considered a more suitable intensity, as it promotes the maintenance of biodiversity and yields higher forest management benefits in the mixed forest of Picea asperata and Abies fabri in Northeast China.