Understanding the processes maintaining tree species diversity is a central problem in ecology,with implications for the conservation and management of forest ecosystems.Although ecologists often assume that trait differences between tree species promote coexistence,empirical evidence connecting functional traits to the niche differences is rare.In this study,we surveyed the regeneration niche of the major coexisting tree species by investigating the physical habitat structure surrounding a seedling in a near-climax mixed temperate forest dominated by Betula albosinensis in Qinling Mountains of China and further measured a suite of functional traits of each seedling.Based the data,we analyzed the differences in regeneration niche and functional traits of seedlings of different tree species,and to test the relationship between regeneration niche and functional traits.