<p>Herbivory acts as a critical biotic filter during seedling establishment, yet the mechanisms by which neighboring plants modulate this pressure remain insufficiently resolved. To simultaneously evaluate the roles of spatial proximity, phylogenetic relatedness, and plant trait contrast, we conducted a three-season field study in a subtropical evergreen broad-leaved forest. We monitored insect herbivory on 1436 woody seedlings and quantified their distance to, phylogenetic relatedness to, and trait contrast with their nearest neighbor seedlings. Our results showed that herbivory consistently increased with greater neighbor distance, supporting a mechanism of distance-dependent associational resistance. Although the distance–herbivory relationship varied in strength among species, phylogenetic relatedness had no detectable effect. Plant trait contrast, specifically in size-related traits (height, leaf number, leaf size), was a key driver: seedlings with greater values in these traits relative to their neighbors suffered higher herbivory. This trait-mediated apparency effect was seasonally stable. Overall, our findings demonstrate that in this species-rich system, neighbor effects on seedling herbivory are primarily structured by fine-scale spatial arrangement and morphological trait disparities, not by phylogenetic kinship. We conclude that spatial proximity and size-related trait contrasts are the key drivers of neighbor effect in this system, and that future research should prioritize trait- and space-explicit frameworks over phylogeny-based approaches.</p>