Quantitative classification of MRT, CCA ordination, and species diversity along elevation gradients of a natural secondary forest in the Qinling mountains

The quantitative analysis of species diversity,forest community classification,and ordination are the basis for secondary forest vegetation protection and restoration,and therefore,has fundamental theoretical significance. Forest community classification,ordination,and species diversity along elevation gradients can reveal the relationships between species distribution and environmental factors,and can provide an important basis for understanding the function of mountain ecosystems. Zhouzhi Nature Reserve is located in the middle of the North slope of the Qinling mountains. It is rich in species diversity,and the vegetation is representative and typical of the area. In this study,we collected data from five sites along the elevation gradient,and aimed to determine the relationships of different forest communities and the environment,and the variation of species diversity along the elevation gradient. The diversity was analyzed using the richness,Shannon-Wiener,and Pielou indexes to represent the diversity of forest vegetation communities at all levels; the forest community was classified using multiple regression trees( MRT),and ordination using canonical correspondence analysis( CCA). Results were as follows:( 1) There were 195 plant species belonging to 61 families and 128 genera in 25plots; Gramineae and Compositae were the dominant families. The species diversity variation along the elevation gradient was similar,showing a significant unimodal distribution pattern,and as the elevation increased,it reached a maximum value of 1600-1800 m,then decreased. The forest community structure and vertical pattern of species diversity varied withthe elevation gradient,revealing a significant biodiversity environment gradient variation relationship;( 2) Through the MRT analysis,we found the forest community was divided into two categories by cross validation: 1. Populus purdomii +Malus kansuensis + Duchesnea indica,2. Quercus aliena var. acuteserrata + Cotinus coggygria + Rubia cordifolia;( 3) The results of CCA clearly reflected the distribution range of various community types and better reflected relationships between species distribution and environmental factors. In addition,elevation,aspect,litter layer thickness,and disturbance were important factors that affected the distribution patterns of secondary forests in the region. The first axis of CCA was mainly related to elevation and litter layer thickness,and the second axis was mainly related to aspect. Clas