The dynamics of conspecific tree and seedling neighbors on seedling survival in a subtropical forest

Abstract

Negative intraspecific interactions could provide opportunities for heterospecific regeneration, thereby maintaining species coexistence in forest communities. Increasing conspecific tree and seedling neighbor densities often have negative correlations with seedling survival. If and how the strength of interactions change with seedling age remains a knowledge gap. In this study, we followed 2184 newly germinated seedlings belonging to 26 species for five years in a subtropical evergreen broad-leaved forest in eastern China. We tested the density distribution pattern of different aged live seedlings and used generalized linear mixed models to assess the dynamic influence of conspecific tree and seedling neighbors on seedlings survival across years. Our results showed that the density distribution of newly germinated seedlings was more clustered than the other aged live seedlings. Over five years, the clustered density distribution of live seedlings gradually weakened. Particularly, the density distribution of five years old seedlings was statistically random. Meanwhile, the degree of positive correlation between the density of live seedlings and the density of conspecific tree neighbors decreased with seedling age. Correspondingly, the conspecific seedling neighbors had a significant negative correlation with newly germinated seedlings survival in the first year and had a greater effect than conspecific tree neighbor density. As seedlings age, the conspecific tree neighbors had a greater negative relative effect on seedlings survival than the conspecific seedling neighbors. Our findings demonstrate that intraspecific negative interactions are an important mechanism on seedling survival and the magnitude of those interactions change with seedling age. In younger seedlings, intraspecific negative interactions were mainly from conspecific seedling neighbors and weakened as the seedlings aged. In later seedling ages, the interactions from conspecific tree neighbors dominated. Ultimately, these effects reduce species clumping dynamically and provide space for establishment of heterospecifics which would maintain diversity in the forest.