Study On The Characteristics And Quantitative Relationship Of Plant Communities In The Middle Reaches Of Yarlung Zangbo River

In this paper,the vegetation in the middle reaches of the Yarlung Zangbo River is taken as the research object.Based on the field investigation and the site conditions of the community,the characteristics and quantitative relationship of the plant community in the study area are analyzed comprehensively,and the type of the plant community and its relationship with the environment in the middle reaches of the Yarlung Zangbo River are revealed.The purpose is to provide theoretical basis for the protection,scientific utilization and management of the biodiversity in the middle reaches of the Yarlung Zangbo River.Main research conclusions:(1)According to the investigation of vegetation in the middle reaches of the Yarlung Zangbo River,the flora in this area is relatively poor;gymnosperms and pteridophytes are in an absolute disadvantage in quantity,angiosperms are in a dominant position,dicotyledons are the main group of vascular plants in this area.There are 126 species of vascular plants belonging to 86 genera,40 families in this area,accounting for only 2.19%,7.10%and 19.23%of the total number of vascular plants in Tibet.Among them,there are 3 ferns,3 genera and 3species,gymnosperms,1 family,1 genus and 1 species,angiosperms,36families,82 genera and 122 species.91 species,63 genera,29 families of dicotyledons.(2)In terms of the level of plant genus,86 genera are divided into 12distribution areas,indicating that the flora has a general geographical connection with the world flora;R/T value is 0.21,and the temperate elements are mainly north temperate,indicating that the flora has a typical temperate nature,closely connected with the world temperate,especially the north temperate elements;in terms of the level of plant species,China Himalayas has 63 species,accounting for 50%of the total number of species in the region,originated in Tibet,indicating that the flora of the region has a high degree of endemism,and the flora is closely related to China Himalaya region,indicating that the flora of the region is relatively young in origin.(3)The overall association of dominant species was negative,the association between species was weak,the relationship between species was loose,and species tended to be independent distribution.The variance ratio method showed that VR<1,and the overall species was negatively correlated,W<?²_0.05(24),indicating that the species correlation was not significant.The statistics of?²test showed that the vast majority of species pairs were not significantly correlated and unrelated.The Jaccard correlation index 0?0.3 basically corresponds to the unrelated and non significant species pairs of?²test.The majority of species pairs were 0?0.3.The results of VR test were further verified by?²test and Jaccard index.The results show that the dominant species in this area have weak association,loose interspecific relationship,little competition for resources,and tend to be independent distribution.(4)TWINSPAN classification was used to divide the plant communities of 24 plots into 7 clusters.The results of CCA ordination showed that the distribution of dominant species was consistent with the spatial distribution of cluster.The main environmental factors affecting the plant community distribution and species composition are longitude,altitude and soil texture.The first axis of CCA sequence basically reflects the altitude gradient and longitude of plant community habitat,and the second axis basically reflects the soil texture of plant community habitat.