Study On Riparian Plant Community And Species Diversity In Chongqing Section Of The Yangtze River

In recent years,with the rapid economic development in China,the deterioration of the ecological environment has become increasingly serious,and the river bank ecological problems have become more and more prominent,which has become a key problem restricting the sustainable development of social economy and the construction of a harmonious society in China.As the ecological basis and barrier of the whole basin,the upper reaches of the Yangtze River is the most critical area for the ecological environment protection of the whole basin,and the Three Gorges Reservoir area is the throat of the ecological barrier.Chongqing is located in the core area of the upstream of the Three Gorges Reservoir Area,so it is self-evident that the study of plant community distribution and species diversity in the Chongqing section of the Yangtze River,especially in the fluctuation areas,is of great importance.Based on the field investigation of riparian vegetation in Chongqing section of the Yangtze River,and combined with the methods of floristic analysis,community ecology,cluster analysis and canonical correspondence analysis,the species composition,floristic composition,species diversity,community type distribution,relationship between community and environmental factors,niche breadth and overlap of vegetation in three regions,fluctuation area,transition area and mountain area,were studied.The distribution characteristics of invasive plants and the construction of risk assessment system of invasive plants were systematically studied.The present situation of plant communities and their species diversity in the study area was comprehensively understood,and the ecological problems faced by them were found,in order to provide a basis for the construction of plant community optimization system,ecological restoration and reconstruction on both sides of the Yangtze River,especially in the fluctuation areas in the future.Theoretical basis and practical guidance.The results are as follows:(1)A total of 419 species of vascular plants belonging to 286 genera and 103 families were recorded through field investigation.Among them,there are 32 species belonging to 19 genera and 15 families of ferns,5 species belonging to 4 genera and 3 families of gymnosperms,and 382 species belonging to 263 genera and 85 families of angiosperms,accounting for about 7.11% of the total vascular plants in Chongqing.Compositae and Gramineae are the most abundant species in the region,while middle families and few species and genera are dominant.The distribution types of families and genera are mainly tropical and temperate,which reflects the transitional characteristics of the Chongqing section of the Yangtze River between the central subtropical and the northern subtropical.The growth pattern of plants is dominated by herbaceous plants,shrubs and trees are few and dwarfing,and some sample plots of trees are missing.Annual plants are dominant in plant life-style fading area and transition area,while high bud plants are dominant in mountainous area,and the proportion of annual plants declines significantly.(2)Twenty-eight sample points were selected,and the sample zones were set up along the vertical direction of the current and the beginning of the falling area.According to the altitude,the sample zones were divided into the fluctuation area: 145-175 m,the transition area: 176-200 m,the mountain area: > 200 m.The total species and diversity of the sample plots,shrub layer and arbor layer were positively correlated with the altitude,and the species number of herbaceous layer was positively correlated with the altitude.The relationship between diversity and altitude was not significant,the correlation was Tree Layer > shrub layer > herbaceous layer;the number of species and diversity index in the south bank was slightly higher than that in the North bank,but the difference was not significant.(3)For the fluctuation area,Shannon Wiener diversity index,Pielou evenness index and Gleason species richness index in the fluctuation area along the upper and lower reaches of the Yangtze River showed a downward trend,while Simpson richness index showed a reverse trend.Shannon Wiener diversity index and Simpson richness index in the fluctuation area had significant differences.Number,Pielou uniformity and Gleason species richness increased with the elevation gradient,while Simpson dominance index showed no significant difference among the four indices,and the difference index and Cady index increased with the elevation gradient.(4)Ward Minimum Variance Clustering classified riparian vegetation into 7 vegetation types and 32 population clusters,including 8 forest types,24 grasses and shrubs.There are 18 species of clumps,15 species of grasses and 3 species of shrubs in the fluctuation area.The most dominant species are Bermudagrass + Paspalum + Echinochloa,and the dominant species are annual herbs.The transition area contains 7 species of clumps,3 species of grasses,5 species of shrubs,the elderberry-humulus + Sumen liquor grasses,and the dominant species are annual herbs,with the proportion of shrubs increasing in the community.There are 8 species clusters and 5 vegetation types in the area,of which the most are Chinese fir and Aralia,and the main vegetation type is evergreen broad-leaved forest.(5)SPearman correlation analysis and CCA sequencing were carried out among plant species,plant communities,diversity and environmental factors in the three research areas.The results showed that the distribution pattern of plant species and communities in different regions was well correlated with elevation,slope,slope direction,herbaceous layer coverage,disturbance intensity,canopy density,soil water content,soil pH value and soil organic matter content.CCA sequencing results showed that disturbance intensity and altitude were the dominant factors affecting the distribution of plant communities in the fluctuation area,while altitude was the dominant factor in the transition area and altitude and slope direction was the dominant factor in the mountain area.In conclusion,altitude is the dominant factor affecting the distribution of plant communities along the river bank.(6)The niche breadth of dominant plants in the fluctuation area was as follows: the fluctuation area > the transition area > the mountain area;68.89% of the species in the fluctuation area had greater niche overlap value than the same species pair in the transition area,88.89% had greater niche overlap value than the mountain area;86.67% of the species in the transition area had greater niche overlap value than the mountain area.Six pairs in the fluctuation area are highly overlapping,mainly with large overlapping pairs;two pairs in the transition area are highly overlapping,mainly with large overlapping pairs;there is no high overlapping in the mountain area,mainly with partial overlapping pairs;the overlapping values of plant niche in the three areas are generally as follows: the fluctuation area > the transition area > the mountain area,indicating that the fluctuation area is still in the primary stage of succession.(7)A total of 32 species of invasive alien plants belonging to 28 genera and 13 families were found in Chongqing section of the Yangtze River,of which Compositae and Amaranthaceae are the most abundant,accounting for 40.63% and 12.50% of the total,North America is the most abundant invasive species,and annual herbs are the main habitat.87.50% of invasive plants are widely distributed in Chongqing,and the invasion phenomenon needs to be paid more attention.The distribution of invasive plants in the main urban area is relatively small,and the regional distribution far from the urban area is obviously increased;the distribution of invasive plants in Yongchuan,Jiangjin,Banan,Fengjie and Wushan counties is the largest;among them,loquat,Bidens bipinnata,Liquor grass,Lotus philoxeroides and wild carrots are widely distributed and abundant throughout the survey area,with Eupatorium adenophorum,Herba Potentillae and Pennisetum vulgaris widely distributed and abundant.There are more distribution in the upstream of Chongqing section.Among the three regions,the number of invasive plants in the fluctuation area > the transition area > the mountain area,and the plant invasion in the fluctuation area is the most serious.The analysis of invasion risk system shows that 21.88% of invasive species are at high risk,and the phenomenon of plant invasion is serious.It is urgent to adopt scientific methods to control the disease.