Aim: Most studies on latitudinal gradients of biodiversity have focused on gradients of species richness. Here we aim to test whether, on top of these strong diversity gradients, processes of community assembly vary along a latitudinal gradient of more than 33°. Location: China, latitude 18.67-51.86° N. Methods: We used species abundance distribution (SAD) data collected in 32 forest tree plots, and fitted a non-neutral model of community assembly to these SADs. We then calculated the fitted deviation from neutrality, δ, and looked for correlations between δ and geographical and environmental data. Results: The fitted parameter δ was positive in most plots, and was furthermore positively correlated with latitude and negatively with temperature, indicating a less even abundance distribution and a likely increase in the strength of environmental filtering in regions further from the tropics and with decreasing temperatures. These results imply that on top of reducing the species richness, cold temperature may impact community assembly processes by strengthening local environmental filtering. Main conclusions: Our results suggest a latitudinal gradient in tree community assembly process in Chinese forests, in which deviations from neutrality increase with latitude, probably because of an increase in environmental harshness.