Drought amplifies divergence between the responses of radial growth and resin duct traits to neighbourhood competition.

Drought and neighbourhood competition can affect tree growth and resin duct traits, yet how competition responses differ between drought and non-drought conditions remains unclear. We combined tree-ring basal area increment (BAI) with six resin duct traits for 75 focal Larix principis-rupprechtii trees across five study locations in northern China. Annual radial growth was weakly associated with reconstructed annual competition intensity under both drought and non-drought conditions. In contrast, all six resin duct traits and a principal component analysis (PCA)-derived resin duct index were positively associated with competition intensity during drought years, whereas these relationships were weak or absent during non-drought years, with greater divergence between growth and resin duct responses under drought. This pattern was robust to alternative drought definitions, surface-area standardization, and a four-trait PCA excluding derived total traits. Across complementary distribution-specific and Gaussian log1p Bayesian bivariate models, conditional growth-resin duct correlations were generally weak or uncertain across residual, year, plot/location and individual-tree components, although positive correlations were most evident at the individual-tree level for latewood and total resin duct lumen area. Overall, drought was associated with contrasting competition responses of radial growth and resin duct traits without producing a consistent growth-resin duct correlation structure, highlighting environmentally contingent and trait-specific responses to neighbourhood competition in drought-prone forests.