Abstract:

Aims: Seedling recruitment is a critical process for maintaining the health and sustainability of forest ecosystems. Numerous studies have demonstrated that compared to niche differentiation caused by resource competition, negative density-dependent effects driven by biological interactions among neighboring seedlings have a stronger impact on seedling survival. However, it remain elusive how the symbiotic networks formed by ectomycorrhizal fungi and host trees regulate the seedling recruitment. 

Method: In this study, seedling surveys were conducted in an old-growth broad-leaved Korean pine forest and two secondary forests—a poplar and birch forest, and a coniferous and broad-leaved mixed forest—which established following disturbances such as logging and wildfires on Changbai Mountain. Here we aimed to investigate the effects of different succession stages and the proportion of ectomycorrhizal (EcM) tree species on seedling recruitment. Additionally, the study identifies and examines the key factors affecting seedling recruitment across different successional stages. 

Results: The results showed that seedling growth and mortality rates varied significantly across forest successional stages, with both rate being lower in broad-leaved Korean pine forest than those in two secondary forests. An increased proportion of EcM tree species significantly affected seedling growth and mortality in broad-leaved Korean pine forest. Although a higher EcM tree proportion promoted seedling growth, it also exacerbated resource competition, resulting in enhanced seedling mortality. Furthermore, the critical factors affecting seedling recruitment were found to depend on forest successional stage. During the early and middle successional stages, environmental factors, such as total soil nitrogen and pH, were the primary drivers of seedling survival. In contrast, during the late successional stage, seedling survival appeared to be influenced by both conspecific density constraints and heterospecific protective effects, with conspecific and heterospecific seedling neighborhood density becoming the dominant factors affecting seedling survival. 

Conclusions: The effects of EcM species proportion on seedling recruitment exhibit significant stage-specific differences across succession phases, with dominant influencing factors undergoing substantial shifts throughout the process. These findings provide empirical support for advancing temperate forest tree recruitment strategies, guiding effective forest restoration efforts, and enhancing long-term ecosystem stability and productivity.

Key words: successional stages, ectomycorrhizal tree species, seedling renewal, temperate forest ecosystem