Crown architecture traits mediate shade tolerance-dependent trade-offs and neighborhood interactions in a subtropical forest

Crown architectural traits are critical adaptations that balance light capture with mechanical stability. Given that light availability plays a fundamental role in shaping forest community structure, co-occurring tree species of different shade tolerance guilds exhibit distinct resource acquisition strategies. However, how shade tolerance governs multidimensional crown architecture and mediates neighborhood interactions remains unclear. In a subtropical Chinese forest, we monitored 5-year growth and measured six individual-level crown traits for 3589 trees. We quantified trade-offs among crown traits and evaluated the relative effects of tree size, spatial structure, neighborhood density, and crown trait dissimilarity on growth across shade tolerance guilds. Principal component analysis revealed two major axes: crown shape (PC1, narrow-deep vs. broad-shallow) and crown size (PC2, height and apical dominance). Light-demanding species exhibited higher scores along the crown size axis, consistent with a strategy of rapid vertical growth, whereas shade-tolerant species showed more plastic crown forms, advantageous for persistence under low light conditions. The influence of crown trait-mediated neighborhood interactions on growth also diverged between shade tolerance guilds. Growth of light-demanding species was suppressed by dissimilarity in apical dominance ratio and crown shape (PC1), yet enhanced by dissimilarity in crown projection area, reflecting both environmental filtering and niche differentiation. In contrast, shade-tolerant species were mainly constrained by neighborhood density, consistent with density dependent effects potentially linked to natural enemies. These findings demonstrate that shade tolerance structures crown trait trade-offs and determines how crown traits mediate neighborhood interactions, thereby improving our understanding of crown architecture-driven demography and coexistence in forest ecosystems under global change. • Crown trait is structured along two axes, namely crown shape (narrow-deep vs. broad-shallow) and crown size (height and apical dominance), capturing multidimensional trade-offs in tree architecture. • Shade tolerance mediates ecological strategies demonstrated by crown traits. Light-demanding species occupy higher positions on the crown size axis, reflecting taller stature and narrower crowns to maximize light capture. • Shade tolerance shapes crown-mediated neighborhood interactions. Crown trait dissimilarity strongly influences growth of light-demanding species, whereas shade-tolerant species are primarily constrained by conspecific density dependent effects.