Study On Vegetation And Plant Diversity Of Riparian In The Middle And Lower Reaches Of The Jialing River

Jialing River originates from the Qinling Mountains and crosses Shanxi,Gansu,Sichuan and Chongqing provinces(municipalities).It is one of the eight tributaries in the Yangtze River basin and the largest tributary in the upper reaches of the Yangtze River basin.Vegetation types and their stability on both sides of the Jialing River Basin directly affect the ecological environment of this basin.Therefore,the study of vegetation and plant diversity in this basin is of great significance to the ecological protection and utilization,restoration and reconstruction,soil erosion and stability.At present,there are relatively few studies on vegetation and plant diversity in Jialing River Basin.This paper takes the vegetation and plant diversity in the middle and lower reaches of the Jialing River basin as a research object,and conducts field surveys from July 2017 to October 2018.We set up 13 vertical flow lines perpendicular to the basin,70 typical representative squares,and 32 typical herb community plots according to the topography and vegetation characteristics of the two banks.On this basis,combined with relevant literature,using plant fauna,population ecology,community ecology,vegetation ecology,biological invasion theory and other research methods,from the composition and floristic characteristics,spatial distribution pattern of the vegetation and community sorting,comprehensive and systematic analysis of plants and vegetation on both sides of the middle and lower reaches,with reference to classification,correlation and niche,species diversity and environmental factors,invasive plant distribution and risk assessment,with a view to providing watershed development and protection,utilization and ecological environment restoration.The results of the analysis are as follows:(1)The sample quadrats and lines survey obtained 510 species of vascular plants belonging to 332 genera and 113 families in the Jialing River basin.Among them,there are 41 species,25 genera and 17 families of ferns,8 species,8 genera and 4 families of gymnosperms,461 species,300 genera and 92 families of angiosperm of all species,they are made of 367 species,242 genera and 80 families of dicotyledons and 94 species,58 genera and 12 families of monocotyledons.Gramineae,Cyperaceae Plants are dominant species of them.The fern,gymnosperm,dicotyledons and monocotyledons respectively accounted for 8.04%,1.57%,71.96% and 18.43% of all the vascular plants in the Jialing River basin.The distribution types of plant family and genus in the middle and lower reaches are diverse,but the tropical and the temperate distribution are dominant.The distribution types are compatible with the subtropical humid monsoon climate of the Jialing River Basin.(2)The results of vegetation spatial distribution pattern analysis showed that the vegetation in the middle and lower reaches of the basin is distinct and the seasons are significant in the vertical direction of the hilly area.In flat region,the vegetation is mainly based on agro-ecological.The results of Ward clustering analysis showed that the vegetation on both sides of the middle and lower reaches was divided into six vegetation types such as warm evergreen coniferous forest,deciduous broad-leaved forest,coniferous and broad-leaved mixed forest,bamboo forest,shrub and grass.There are 23 clusters,which were Ass.Pinus tabulaeformis+ Pinus massoniana,Ass.Pinus massoniana-Vitex negundo+Rhus chinensis,Ass.Cupressus funebris,Ass.Pinus massoniana+Symplocos setchuensis,Ass.Quercus acutissima-Myrsine africana-Eriophorum comosum,Ass.Alnus cremastogyne-Coriaria nepalensis-Imperata koenigii,Ass.Robinia pseudoacacia+Broussonetia papyrifera-Vitex negundoImperata koenigii,Ass.Populus adenopoda-Broussonetia papyrifera-Cynodon dactylon,Ass.Broussonetia papyrifera-Humulus scandens,Ass.Quercus fabri-Vitex negundo-Imperata koenigii,Ass.Dalbergia hupeana-Rhus chinensis-Imperata koenigii,Ass.Neosinocalamus affinis,Ass.Vitex negundo+Coriaria nepalensis,Ass.Rhus chinensis+Platycarya strobilacea,Ass.Imperata koenigii+Kalimeris indica,Ass.Cynodon dactylon+ Alternanthera philoxeroides,Ass.Eriophorum comosum,Ass.Oxalis corniculata,Eleusine indica.The C.funebris distribution is the most.The results of the CCA analysis showed that altitude is the main factor that causes the difference of plant community and species composition.(3)The results of niche analysis showed that there were significant differences in niche breadth and niche overlap between the 15 dominant woody plants and 25 dominant herbaceous plants in the middle and lower reaches.The highest value of niche breadth of the woody plants in the middle and lower reaches is C.funebris,followed by Vitex negundo and B.papyrifera.The niche breadth of the ridges are C.funebris,V.negundo and R.chinensis,and the middle slope are V.negundo,P.massoniana and P.massoniana.The top three of niche breadth are B.papyrifera,Robinia pseudoacacia and Neosinocalamus affinis.There are many differences in the composition of dominant species in different regions.The C.funebris has the largest distribution area in the middle and lower reaches,and strong adaptability to the environment.The chance of large overlap and high overlap of woody plants niche overlap value(NC)is mid-slope < water-falling zone < ridge in different study regions.The largest niche breadth of the dominant herbaceous plants in the middle and lower reaches are I.koenigii,C.brunnea,and K.indica,which indicat that the distribution of them are the widest.In the ridges,the top three of niche breadth are K.indica,C.brunnea and I.koenigii.The mid-slope are Ficus tikoua,Arthraxon hispidus,C.brunnea,and the water-falling zone are A.philoxeroides,C.dactylon and Humulus scandens.The overlap values of niche of the dominant herbs in different research sections are difference which is water-falling zone <mid slope < ridge.In conclusion,niche of the dominant plants are differences and significant in different research sections.The results of niche analysis are consistent with the clustering classification of riparian plant communities.(4)The results of plant community diversity analysis showed that the overall change trend of the Margalef index,Pielou evenness index,Shannon-wiener index and Simpson diversity index curves in the middle and lower reaches were basically consistent.The diversity index increased with Margalef and Pielou.There is a significant difference in diversity between different regions.The four-index fitting curves increases first and then decreases in the mid-reach and the lower reach gradually increases.In the vertical direction,with the increase of altitude(distance),the ? diversity index and uniformity index change are water-falling zone < mid slope < ridge,and the Margalef index is ridge <middle slope< water-falling zone.In the same research section,the Pielou index and diversity index have the same trend and the Margalef index is significant difference.The trend is consistent with the horizontal direction.With the increase of altitude,the Cody index gradually decreases and Jaccard index increases.(5)The diversity of herbaceous plants in the middle and lower reaches of the water-falling zone showed that the Margalef index ranged from 3.66 to 9.14,and the Pielou index from 8.31 to 9.51.The Shannon-wiener diversity index and the Simpson diversity index are basically the same,and the variation respectively ranges are 2.12-3.78 and 0.871-0.974.The four-index fitting curves reflects the same trend,which decreases first and then increases in the middle reach and has a small range of variation in the lower reach.This indicates that the difference in species composition is not the same,the dominant species not obvious and the interference intensity is different between the middle and lower.The SPSS analysis showed that the plants diversity index was no significant difference between the mid-stream and downstream(P>0.05).There was a significant difference between the natural fall zone and the Water-level-fluctuating zone(P<0.01).That indicates that the plant diversity has been decreased for the construction and operation of the power station.The Jaccard index of the ?-diversity showed a “W” change,in which the middle was “V” and the lower was “U”.The Cody species substitution rate showed “M” along the middle and lower reaches,which were opposite to the Jaccard index.The plant diversity has been strongly interfered by the construction of the midstream power station and sand mining site.The results of the spatial distribution pattern of dominant herbaceous plants and CCA environmental factor ranking analysis showed that the distribution of dominant herbaceous plants was significantly different from the downstream end point and the distance,altitude,available phosphorus and arbor coverage were the main environmental factors affecting the distribution differences.(6)The results of interspecific association analysis of the dominant herbaceous plants in the middle and lower reaches of the water-falling zone indicated that there is a significant positive association between the dominant herbaceous plants in the middle and lower reaches.The chi-square test results showed that the positive association and negative correlation were roughly equivalent.Ochai index(OI)and Jaccard index(JI)showed that the association intensity between species were low.That indicates that the dominant herbaceous plants were still in the process of succession development,and the stability was weak.The results of the niche breadth and niche overlap analysis showed that the overall niche overlap value was large,and that there is a large competition between the dominant herbaceous communities in the middle and lower reaches of the water-fluctuating zone.In general,the herbaceous plants communities are in the process of succession,and there is greater competition among the dominant species.(7)The analysis results of invasive plants and risk assessment showed that there were 43 invasive plants in the middle and lower reaches,which were widely distributed.Invasive plants were derived from tropical America,accounting for 20.93% of the total number of invasive plants in the middle and lower reaches.The main lifeliness was herbaceous,including 12 species of Compositae,which accounting for 27.91% of the total invasive plants.The distribution of invasive plants in different research sections were ridge <mid slope< water-falling zone.There are 10 kinds of ridges,14 kinds of mid-slopes,30 kinds of water-falling zone,and 23 kinds of mid-streaming belts,17 kinds of downstream distribution areas.The invasive plants were widely distributed in the water-falling zone and it is an important cause of the ecological fragility.