It has been widely confirmed that canopy gap disturbances can promote species richness of forest communities.However,whether plant assemblage within a canopy gap is constrained by local or regional processes remains a contentious issue in plant ecology.To investigate the contrasting roles of local processes and regional processes,we examined the relationships between the number of herbaceous plant species at two small-scales (in 0.25 m ² and 1 m ² quadrats) within the gap and the whole herbaceous plant species in the surrounding gap in the Betula utilis forest of Taibai Mountain.The results showed that:(1)species richness at 0.25 m ² and 1 m ² local scales significantly correlated with the number of available species in the surrounding gap (r=0.791 and r=0.861).And the two local-scales species richness showed a positive function of regional species richness,respectively.But the local and regional species richness significantly increased with increasing gap sizes,which may generate a spurious relationship between local and regional species richness.(2)The significant positive local-regional relationship was persisted controlling for the effect of gap size in multiple regression (R ²=0.642 for 0.25 m ² scale and R ²=0.743 for 1 m ² scale).Moreover,analysis of variance depicted that gap size only explained 4.0% and 4.4% of the variation in local species richness at 0.25 m ² and 1 m ² quadrats,respectively;While,regional species richness accounted for 25.8% and 35.3% after gap size was controlled,respectively.These results suggested that local-scale species richness can be constrained by regional species richness in the surrounding canopy gaps.