Abstract: Pinus massoninana secondary plantation is one of the major single species forest plantations in southern China.Our objective is to expound the variation of the understory community structure in the development process of the major single species forest plantations,to provide a basis and reference for the vegetation ecological improvement of the plantations.We adopted the method of space substitute time,sited a standard plot in the plantations of each age stages to study the species diversity in the communities.Investigation was conducted for different stages of Pinus massoninana plantations,which showed that there were 108 kinds of plants species,56 families under 91 genera in Zijin Mountain National Forest,Hengshan County,Hunan Province.Loropetalum chinensis,Quercus fabri,Radix Syzygii,Gardenia jasminoides and Imperata cylindrica,Schizachyrium scoparium,Lophatherum gracilie and Woodwardia japonica have a greater advantage in the whole community.Before the mature forest (15 years),the index value of the entire community and its diversity is very volatile.New species of wild trees appeared after the mature forest (15 years),while the index value of the whole community tends to bestable.Throughout the evolution of the communities,the species similarity is lowest(S_m of 0.158) between communities of old growth forest (25 years) and young forest (5 years),β diversity the most,reflecting the young forest (5 years) is the most unstable community.

Key words: Pinus massoninana, plantation, vegetation communities, diversity, succession characteristics