Vegetation Classification Based On Mature Community And Gap-disturbance Community In Tiantong Mountain, Zhejiang Province

Vegetation classification is a highly complex issue in the vegetation science.The evergreen broad-leaved forests(EBLFs)are the zonal vegetation in subtropical zone.The community types of EBLFs are diversified.There are many secondary forest communities in EBLFs due to the constant interference of human activities.Those secondary forest communities make the associations division to be more challenging.The 20 hm~2 EBLF dynamic plot in Tiantong(hereafter called Tiantong plot)provided us with the vegetation data of continuous forest community.Based on this,it is helpful to reveal the discontinuity of continuous vegetation.In addition,a large number of gaps were formed by natural disturbances in Tiantong plot.The data of these gaps provide valuable research materials for our study on the division of gap-disturbance community type.In this study,we have divided the type of mature community and gap-disturbance community in Tiantong plot.Using two-way indicator species analysis(TWINSPAN)and detrended correspondence analysis(DCA)removed the transitional community in continuous distribution community.Then TWINSPAN as well as DCA were repeated.We evaluated the classification results using silhouette width.The indicator species was determined by the species indicator value(IndVal).Finally,we analyzed the correlation between environmental factors and community distribution by canonical correspondence analysis(CCA).The mature community of Tiantong plot can be divided into 3 associations in different habitats respectively.They are named by dominant species and indicator species.More specifically,Viburnum erosum-Ternstroemia gymnanthera/Lithocarpus harlandii+Cyclobalanopsis sessilifolia Association was distributed in the habitat of high-altitude slope;Daphniphyllum oldhami-Lithocarpus glaber/Schima superba+Castanopsis carlesii Association was distributed in the habitat of low-altitude slope;and Illicium lanceolatum-Phoebe sheareri/Choerospondias axillaris+Machilus leptophylla Association was distributed in the habitat of valley.According to the correlation analysis of three associations and environmental factors,elevation and convexity had significant effects on the distribution of associations,and slope and aspect were less affected.We found that the combination of TWINSPAN and DCA is beneficial to find transitional community in continuous community,reveal the discontinuity of the community and finally identify typical types.In 2010,the gap-disturbance community could be divided into three community types.They were generally consistent with three associations in the mature community.With the progress of succession,in 2015,there was a new community type in the gap-disturbance community that were influenced by the historical disturbance community in the plot.And this new community was similar to species composition of the historical disturbance community.Forest gaps have created conditions for the diffusion of species in neighboring community,the species composition of the gap-disturbance community changed.Compared with three associations of mature community,the forest gaps had become more homogenous.This causes many difficulties for the classification based on plant species composition.In conclusion,the removal of transitional community is of great significance to identify typical types in continuously distributed forest.It is helpful to find the transitional community more intuitively by combining TWINSPAN and DCA based on species composition.Forest gaps make the relationship between gap-disturbance community,environmental conditions and its surrounding community more complex.This reminds us that we need to be cautious in dealing with the classification of gap-disturbance community.Our research is an attempt to classify the vegetation on the basis of a large forest dynamics plot.It provides new ideas for the vegetation classification of forest community with continuous distribution on a certain scale,and provides methodological references for vegetation classification of EBLFs with strong secondary and transitional communities.