Abstract: The forest ecosystem on south slope of the Funiu Mountain was investigated by using community ecological techniques.Data thus collected were used to calculate importance values of the plant species,which were in turn used to designate eight plant functional groups(PFGs).Employing respectively Levin’s formula and the percentage of similarity formula,we calculated niche breadths and overlaps of 7 species of trees,14 species of shrubs and 4 species of herbs populations constituting the PFGs.The results showed that:(1)Species of high importance values usually had relatively bread niches,which were frequently accompanied by high levels of niche overlap;(2)High levels of niche overlap could result from patchiness and heterogeneity of suitable habitats;(3)Niche breadth variations along the altitudinal(precipitation and temperature)gradients reflected changes in the ability of the species constituting PFGs to adapt to different environments and exploit different resources,these changes would eventually lead to shifts in PFG compositions.