Study On Vegetation Characteristics Of Xixiang Basin In Qinba Mountain Area

There are many small basins and valleys connected between the Qinling Mountains and the Daba Mountains.Xixiang Basin is one of them.Its unique geographical location and superior natural climate make the local species resources extremely rich.Therefore,this study carried out a comprehensive field survey of natural vegetation in Xixiang Basin,set up36 sample plots by systematic sampling method,and made a statistical analysis of the vegetation data obtained from the survey.The vegetation characteristics of Xixiang Basin in Qinba Mountains were elaborated from four aspects of flora,species diversity,classification and ordination,as well as interspecific relations.It provides theoretical basis for rational exploitation and utilization of plant resources and protection of rare and endangered plants in the area.The main conclusions are as follows:(1)This survey recorded 1,030 species of plants in the Xixiang Basin in the Qinba Mountains,belonging to 546 genera and 142 families.Among them,pteridophytes include14 families,23 genera and 38 species,gymnosperms include 4 families,9 genera and 14species,and angiosperms include 124 families,514 genera and 978 species.Among the angiosperms,monocots contain 107 species in 66 genera and 20 families,and dicots contain871 species in 104 families and 448 genera.The genera of the 523 genera of seed plants obtained by statistics are divided into 15 distribution types and 18 variants.44.36%of the total genera are temperate distribution,a total of 232 genera,and the tropical distribution is the second,with 145 genera,accounting for 27.72%of the total genera in the study area.(2)The analysis and comparison of the four species diversity of different life forms in the Xixiang Basin in the Qinba Mountains show that the species richness,dominance index and diversity index basically appear as herb layer>shrub layer>arbor layer.The evenness index basically shows that the shrub layer is larger than the herb layer and tree layer.Using the Generalized Additive Model(GAM)analysis,it is concluded that the diversity index of different levels of vegetation shows different diversity patterns with the change of altitude.Among them,the species richness and diversity index of the shrub layer is significant at the level of 0.05.Correlation,showing that it increases with the elevation,the dominance index of the shrub layer is significantly correlated with the elevation at the level of 0.1,and it also shows an upward trend with the elevation,and the other indexes do not show a relationship with the altitude.Significant relationship.(3)The vegetation of the Xixiang Basin in the Qinba Mountains is divided into the Paulownia tomentosa+Cocculus orbiculatus+Eschenbachia japonica community and the Juglans mandshurica+Helwingia chinensis+Hylodesmum podocarpum community through the multiple regression tree(MRT).Through the Canonical Correspondence Analysis(CCA),it is concluded that the three environmental factors of altitude,slope and latitude not only have a significant effect on the distribution of vegetation in the Xixiang Basin in the Qinba Mountains,but also have a significant impact on the distribution of 51dominant species.Through the correlation analysis of five environmental factors,it is concluded that the altitude of the Xixiang Basin in the Qinba Mountains is significantly positively correlated with the slope(at the 0.05 level),and significantly negatively correlated with the latitude(at the 0.01 level).(4)The 20 main species in the shrub communities in the Xixiang Basin in the Qinba Mountains showed significant positive associations on the whole,indicating that the local shrub communities are in a stable stage.The?~2test,Pearson correlation test,and Spearman rank correlation test were performed on 190 species pairs.The results showed that most species pairs were insignificantly connected or not significantly correlated,indicating that species pairs have strong independence.By calculating the interspecies association index,the result is relatively consistent with the?~2test result.Combining the analysis results of interspecific association and correlation with the results of principal component analysis(PCA),the main species in the shrub layer of the Xixiang Basin shrub community are divided into three ecological species groups,and the species ecological habits of the same ecological species group It is similar to the way of resource utilization,and most of the species are positively correlated.