Straddling the subtropical and warm-temperate zones of East China, the FuNiu Mountain National Natural Reserve is representative of north-south climatic transition zones. The vegetation in this natural reserve is well protected. Highly species rich, the understory layer is nonetheless mainly composed of a small number of dominant species whose abundances clearly vary along environmental (altitudinal) gradients. The shrubs appear to be greatly influenced by the trees. This may indicate that trees exert a certain degree of control over the renewal of the arboreal layer. Highly responsive to changes in environmental conditions, herbaceous plants are very useful to the study of vegetation-environment dynamics. Using community ecology techniques, we investigated plant assemblages on both the north and south slopes of the FuNiu Mountain. Results of this investigation were used to calculate species importance values, which in turn were used to identify dominant species. X2 test, together with association coefficient (AC) and percentage co-occurrence (PC), were used to measure interspecific associations of the dominant herbaceous species. PFTs were defined according to interspecific associations and altitudinal distributions of the dominant herbaceous species of the understory layer. Dynamics of these PFTs along moisture and temperature gradients were analyzed. The results of this study show that, in studies of forest understory plant assemblages, designating PFTs according to dominant herbaceous species is feasible, and PFTs thus defined are representative. Seven PFTs, each with its unique spatial distribution and morphological characteristics, are identified: campanion, alpine, dank, drought-resistant, forest gap, basic, primeval. These PFTs appear to reflect vegetation-environment dynamics well. This study may contribute to future studies on forest ecosystems and PFTs classification methods.