Study on Species Competition and Diversity Assembly Mechanisms in Neighborhood Scale in the Subtropical Natural Secondary Forests of Chishui, Guizhou

Subtropical evergreen broadleaf forests are among the forest types most affected by human activities. Following the destruction of primary forests, a multitude of pioneer species initiates secondary succession, not only altering the ratio and community structure between evergreen and deciduous species in natural forests but also profoundly impacting species coexistence, community succession and the recovery of secondary forests. In this context, this study was conducted in a fixed plot within a secondary forest, nearly 40 years post-restoration under in-situ conservation policies. We surveyed and spatially positioned 2 162 tree individuals from 37 species, each with more than ten individuals, identifying species and dividing them into three key groups: evergreen, deciduous broadleaf and plantation forests for analysis. The aim was to elucidate the mechanisms of species coexistence and diversity construction during the early stages of secondary forest restoration, providing a scientific reference for future forest conservation and restoration projects. The results are as follows: (1) Within the community, secondary deciduous species and plantation species of Cunninghamia are dominant, while native evergreen broadleaf species like Castanopsis and Schima have become less prevalent; (2) At a small scale, evergreen and deciduous broadleaf species significantly cluster, exhibiting a deterministic process that promotes neighborhood diversity construction. Adjacent evergreen and deciduous saplings are highly intermixed in height, yet interspecific competition shows significant positive associations and symmetry; (3) Compared to deciduous and plantation forests, evergreen broadleaf species not only exhibit significant symmetry in intraspecific competition processes but also play a stronger role in enhancing neighborhood species diversity. These findings suggest that in the early stages of subtropical secondary forest restoration, niche differentiation and symmetric competition processes between evergreen and deciduous species are closely linked and may be key mechanisms in secondary forest recovery. The deterministic processes guided by niche theory play a relatively important role in promoting the recovery of neighborhood species diversity, particularly the potential for late-stage recovery in evergreen broadleaf forests.