Taxonomic diversity effects on forest productivity and response to
climate extremes range from positive to negative, suggesting a key role
for complex interactions among neighbouring trees. To elucidate how
neutral interactions, hierarchical competition and resource partitioning
between neighbours shape tree growth and climate response in a highly
diverse Amazonian forest, we combined 30 years of tree censuses with
measurements of water and carbon related traits. We modelled individual
tree growth response to climate and neighbourhood to disentangle the
relative effect of neighbourhood densities, trait hierarchies and
dissimilarities. While neighbourhood densities consistently decreased
tree growth, trait dissimilarity increased it, and both influenced
climate response. Greater water conservatism provided a competitive
advantage to focal trees in normal years, but water spender neighbours
reduced this effect in dry years. By highlighting the importance of
density and trait-mediated neighbourhood interactions, our study offers
a way towards improving predictions of forest response to climate
change.