Classification,ordination,and succession of secondary forests in Xiaolongshan National Nature Reserve in west Qinling

Based on the field investigation data and by using two-way indicator species analysis(TWINSPAN) and detrended correspondence analysis(DCA),a quantitative classification and ordination of the secondary forest communities in the Xiaolongshan National Nature Reserve was conducted,and the spatial distribution patterns of the vegetation communities were studied from the species composition and the ecological relationships of plant communities and environment,aimed to understand the succession of secondary forests in the Reserve,and give a rational environmental explanation.According to TWINSPAN,the forest communities in the Reserve were classified into 12 types.The DCA ordination graph distinctly reflected the ecological significances of the ordination axes.The horizontal axis basically reflected the variation of humidity,which increased gradually from left to right,and the vertical axis basically reflected the temperature gradient,which decreased from down to up.The succession pattern of the secondary forests was in the sequence of Populus davidiana forest → P.davidiana + Betula platyphylla forest → Quercus aliena var.acuteserrata pure forest or mixed forest,with Q.aliena var.acuteserrata forest as the climax community in the process of natural succession.