Fluctuations in Species Diversity in Evergreen Broad-Leaved Forests and Changes in Their Co-Occurrence Network

Understanding the population dynamics and interspecific interactions in subtropical forests is crucial for uncovering the underlying mechanisms of species coexistence and community stability. Two censuses were conducted between 2018 and 2023 in a 9.6 ha subtropical evergreen broad-leaved forest dynamics plot situated in Mount Wuyi, southeastern China. Utilizing co-occurrence networks and long-term data, we examined the relationship between species interactions and their contributions to community assembly. Our findings reveal that high mortality rates among small-diameter individuals have created ecological niches, facilitating the establishment of 12 new species between 2018 and 2023. A generalized linear mixed-effects model showed positive relationships between sapling abundance and conspecific neighbor density. Co-occurrence networks demonstrated a shift toward higher positive interactions but reduced modularity, indicating a more integrated yet less stable community structure. Despite their low abundance, rare species demonstrated significant roles in network connectivity and stability, underscoring their status as keystone species. Additionally, the significant correlations between topographic factors and species richness highlighted the role of environmental filtering in shaping community composition. Our findings contribute to a deeper understanding of subtropical forest community dynamics, emphasizing the importance of long-term monitoring to unravel the complex interactions between populations and their environmental conditions. This study represents the first long-term observational experiment conducted in a subtropical secondary forest, providing valuable insights into the dynamics of forest community assembly in this region.