Classification,Ordination And Influencing Factors Of Typical Vegetation Community In Ganquan County,Loess Region Of Northern Shaanxi

Ganquan County belongs to the typical hilly and gully area of the Loess Plateau in northern Shaanxi,with diverse topography and abundant vegetation resources,which are typical and representative in the entire Loess Plateau.The research on the vegetation characteristics of Ganquan County provides theoretical basis and reference for the protection of vegetation diversity in the Loess Plateau and the selection of species for returning farmland to forests.In this study,the vegetation of Ganquan County was comprehensively investigated,and 36 sample plots were established.The vegetation community in the sample plot was analyzed from four aspects:quantitative classification,species diversity,floristic division of genera,dominant shrub niche and interspecific linkages,and the following conclusions were drawn:(1)The 16 broad-leaved forest plots in Ganquan County were divided into the following two communities by multiple regression tree(MRT):CommunityⅠAcer tataricum subsp.Ginnala+Periploca sepium+Elymus dahuricus community,community II:Quercus mongolica+Rosa xanthina+Tripogon chinensis community.The CCA outcome showed that the four environmental factors of altitude,slope position,latitude and slope had particularly notable impact on the distribution of the plots,among which altitude had a very significant impact on the distribution of the plots.The three explanatory variables of altitude,slope position and latitude have significant effects on the distribution of dominant species,among which altitude has a very significant impact on the distribution of dominant species.(2)A total of 409 species of plants in Ganquan County were recorded in this survey,belonging to 88 families and 268 genera,most of which are angiosperms,with a total of 82families,262 genera and 401 species,accounting for 98.04%of the total species.Gymnosperms and ferns account for less.,is 1.95%.The 268 genera of Ganquan County were divided into 14 distribution types and 16 distribution subtypes,of which the temperate distribution was the most,with 143 genera,accounting for 53.36%of the total number of genera,followed by the tropical distribution with 59 genera,accounting for 22.01%.(3)The species richness,vegetation Simpson dominance index and vegetation Shannon-Wiener diversity index in theαdiversity index of the vegetation community in the36 sample plots in Ganquan County generally showed the situation of herb layer>shrub layer>tree layer.It can be seen that the tree layer is larger than the shrub layer,and the vegetation Pielou index shows a more complex pattern.There are a considerable number of plots in the tree layer and the shrub layer.The herb layer is higher than the shrub layer.Altitude had a significant effect on species richness of tree layer and shrub layer,showing a high-order regression relationship.The species diversity index of the other layers showed a linear relationship with the altitude,among which the altitude and the species richness of the herb layer showed a significant linear relationship.(4)The order of the Levins niche breadth index and the Shannon niche breadth index of the 14 dominant shrub populations in the shrub community were generally consistent.The largest niche breadth was Rosa xanthina,and the smallest was Prinsepia uniflora and Hippophae rhamnoides.The 14 dominant populations were divided into 1 specialized species,1 generalized species and 12 neutral populations based on niche breadth.Among the pairs of niche overlap index pairs,the niche overlap index is higher,accounting for 1.99%of the total logarithm,71 pairs are between 0.17-0.86,accounting for 78.02%of the total logarithm,and the niche overlap is small.19 pairs,accounting for 20.88%of the total pairs.The dominant shrub population in the shrub layer generally showed a significant negative association.The positive and negative correlation ratios of theχ~2test,the Pearson correlation coefficient test and the Spearman rank correlation coefficient test were 1.167,0.75,and1.022,close to irrelevance in general,indicating that the shrub community in a relatively stable state.The association coefficient AC was consistent with theχ~2test results.