# Seasonal Variation of the Effects of Phylogenetic Relatedness and Functional Similarity Among Heterospecific Neighbors and Habitat on Seedling Survival in a Subtropical Forest in Gaoligong Mountains, Southwest China

## TL;DR

The study shows that seedling survival in a subtropical forest changes with the seasons, with different factors like rainfall and light availability affecting survival in dry and rainy seasons.

## Contribution

The study reveals seasonal shifts in the effects of phylogenetic and functional density dependence and abiotic factors on seedling survival in subtropical forests.

## Key findings

- Phylogenetic and functional negative density dependence (PNDD/FNDD) strongly influence seedling survival during the rainy season.
- Canopy openness significantly enhances seedling survival during the dry season.
- Seasonal variability modulates the strength of biotic and abiotic drivers of seedling survival.

## Abstract

Understanding the mechanisms of species coexistence is a long‐standing goal in community ecology. The performance of woody seedlings across different ecological niches has been proposed as a key mechanism in community assembly. Factors influencing seedling survival can be revealed by analyzing neighboring plants in conjunction with their phylogenetic relatedness, functional traits, and the surrounding environment. In the present study, we conducted a seasonal analysis of 936 seedlings for 56 species from a 4‐ha subtropical forest over 3 years in the Gaoligong Mountains, Southwest China. Our aims were to examine the relative effects of neighbor density, habitat conditions, and seasonal climate variability on seedling survival during dry and rainy seasons, and to determine whether the sensitivity of seedling survival responding to neighbor densities and abiotic factors differs between seasons. The findings indicated that the relative importance of neighbor densities, habitat factors as well as seasonal rainfall on seedling survival varied with seasonality. During the rainy season, seedling survival was comparatively less affected by conspecific neighbor density and was mainly negatively influenced by rainfall, whereas habitat factors (including topography, soil properties, and canopy openness) were detrimental for survival to a lesser extent. There is evidence suggesting that phylogenetic negative density dependence (PNDD) and functional negative density dependence (FNDD) are more pronounced in the rainy season. In contrast, the positive effect of canopy openness was more important during the dry season. Our findings further revealed that the effects of PNDD, FNDD, canopy openness, and seasonal rainfall varied widely among species across seasons. Moreover, species differed in their ability to respond to the trade‐offs between canopy openness and rainfall in relation to phylogenetic relatedness and functional dissimilarity during the dry and rainy seasons. Overall, our results demonstrate that seasonality modulates the strength and importance of phylogenetic and functional density dependence, habitat preference, and climate for seedling survival in subtropical forests. The seasonal variations in these effects allow species to maintain coexistence across dry and rainy seasons. Consequently, seasonal variability should be accounted for in future studies in understanding the diversity of forest communities.

Based on seedling dynamic data from a subtropic forest in Southwest China, we found phylogenetic negative density dependence (PNDD) and functional negative density dependence (FNDD) on seedling survival in the rainy season, but not in the dry season. In the dry season, greater canopy openness significantly enhanced seedling survival, whereas in the rainy season, higher rainfall intensity unexpectedly lowered survival. These results collectively indicate a marked seasonal shift in the dominant drivers of seedling dynamics—from strong biotic regulation (PNDD/FNDD) in the rainy season to abiotic facilitation (light availability) in the dry season—thereby demonstrating how temporal niche partitioning may stabilize forest communities.