Numerical classification and ordination of forest communities in the Songshan National Nature Reserve

The Songshan National Nature Reserve is located at 115°43'44″-115°50'22″(E),40°29'9″-40°33'35″(N). According to the 68 quadrat data,forest communities in this reserve were investigated by using two-way indicator species analysis (TWINSPAN),detrended correspondence analysis (DCA),and canonical correspondence analysis (CCA). The results showed that the forest communities were classified into 13 types,13 associations,by TWINSPAN. The results of DCA and CCA clearly reflect the relationship between the distribution pattern of forest communities and environmental gradients. The first CCA ordination axis indicates the changes of elevation,litter layer thickness,and soil depth,and along the first CCA ordination axis,the elevation becomes higher,litter layer becomes thicker,and the soil becomes deeper form left to right; The second CCA ordination axis is positively correlated with elevation and slope,and negatively correlated with soil solidity. The elevation is a decisive element to forest community.The ecological meaning of CCA ordination axes is much clearer than that of DCA axes. CCA ordination can simultaneously express similarities of species and environment,and the quadrat location in CCA ordination figure is much closer to each other than that in DCA,and the boundary among forest communities become more ambiguous. Therefore if ordination is combined with classification,the effect of DCA is better than CCA. The results of TWINSPAN,DCA and CCA simultaneously indicates vertical distribution pattern of forest community in this reserve.