A knowledge of plant functional trait variation can help us understand the adaptation strategies of plants to the changing environment and community assembly rules. In this study of a riparian zone in Lijiang River, Southwest China, we investigated three key functional traits from 5418 individuals of 51 species to understand the variation in functional traits of woody plants. These functional traits were (1) specific leaf area[SLA], (2) leaf area[LA], and (3) leaf thickness[LTH]. We performed a generalized linear model and ‘varcomp’ function to partition the variance in the three key functional traits across four nested scales which were plot, species, individual, and leaf in riparian plant communities of the Lijiang River. We found that there were significant differences in the explanation variance of the three key functional traits of main woody plants on the four nested ecological scales in this riparian zone. However, the relative contributions of all three traits across four nested ecological scales were similar and species, individual, leaf and error, and plot explained 0.51-0.70, 0.21-0.22, 0.09-0.20 and 0-0.07 of the total variance, respectively. For all traits, the interspecific variability was the greatest for specific leaf area, leaf area, and leaf thickness were 64%, 70%, and 51%, respectively and was higher than the intraspecific variability for specific leaf area, leaf area, and leaf thickness, which were 34%, 30%, and 44%, respectively. The plot level accounted for a very small percentage of the total variance, despite relatively high species turnover between plots. These results suggest that the variation of plant functional traits was dominated by interspecific variation but also showed a substantial amount of intraspecific trait variability. Thus, the intraspecific variation of functional traits should be taken into account if we want to better understand the assembly rules in plant communities. The lowest or even the lack of variance at the plot level provides substantial support for the idea that trait-based habitat filtering could play an important role in plant community assembly.