Dynamic Characteristics Of Vegetation In Yellow River Beach Wetlands And Its Response To The Environment

Beach wetlands of rivers have important ecological functions in maintaining biodiversity,animal protection,climate regulation and water purification.Due to the continuous encroachment of agricultural development and road construction on the beach wetlands,the Yellow River beach wetlands in Yinchuan Plain have been reduced.Timely and accurate grasp of the vegetation growth status and change trend of beach wetland and its response to environmental factors can help reveal the inner mechanism of beach wetland plant community formation,which is of great significance to the conservation of inland dryland beach wetland and the rapid reconstruction and rational use of plant community.In this study,traditional field surveys were combined with UAV multispectral imaging technology to analyze the spatial distribution characteristics of plants,plant community diversity,the number of dominant species,the intra-year dynamics of functional traits and their responses to environmental factors in a typical natural beach wetland in the Ningxia section.The main findings and conclusions of the study are as follows:(1)Large changes in NDVI dynamics in the study area.Because of the high environmental heterogeneity,NDVI changes and class composition were significantly different within different growing seasons,showing an increasing trend followed by a decreasing trend.The DEM,spatial distribution pattern of plants and the distribution of NDVI values in the study area had a strong correlation,and NDVI was significantly higher in high terrain than in low terrain.The NDVI values all reached the maximum in early August,and the plant biomass decreased as the NDVI decreased with increasing altitude during the peak plant growth period.(2)Soil environment is the basis for plant growth.The spatial distribution of soil nutrients was found to be correlated with the spatial distribution of vegetation by kriging interpolation.Spatial distribution of soil nutrients in Yellow River mudflat wetlands is uneven and there is strong variability in abundance and deficiency.There is a strong correlation between soil nutrients and altitude and distance from the river bank.Total nitrogen,total potassium,alkaline hydrolyzable nitrogen,available phosphorus and organic matter showed strong spatial autocorrelation,and their variability was mainly influenced by structural factors.Altitude and soil physical properties have significant effects on soil nutrients.The response of plants to environmental factors was further analyzed after environmental analysis.(3)There are 15 families,24 genera and 25 species of plants in typical beach wetlands along the Yellow River,and the overall plant species richness is low.In the survey from June to September,the changes of the four diversity indices basically showed a higher diversity of plants in high terrain and a lower diversity of plants in low terrain.Diversity index increases with increasing microtopographic elevation.Pearson correlation analysis and PCA analysis showed that micro elevation and groundwater level were the key influencing factors on the distribution of plant communities in the beach wetlands.The RDA analysis showed that different soil physicochemical factors had different effects on plant diversity in different soil layers.Total nitrogen and organic matter in the 0-10 cm soil layer,total phosphorus and salt content in the 0-60 cm soil layer,alkaline hydrolyzable nitrogen and available phosphorus in the 0-40 cm soil layer and rapidly-available potassium in the 10-20 cm soil layer were closely related to plant diversity,respectively.(4)To study the intra-annual dynamics of the population characteristics and functional traits of the dominant species(Phragmites australis,Typha minima,and Calamagrostis pseudophragmites)in beach wetlands and their responses to environmental factors.Phragmites australis are found to be widely distributed in high,medium and low terrain,with a wide ecological niche,capable of being distributed at different altitudes and on different slopes.The Typha minima is more suitable for survival in medium terrain and has a narrower ecological niche.Calamagrostis pseudophragmites is more suitable for habitats with less soil moisture in high terrain.The population size,individual plant biomass and functional traits of the dominant species were in a dynamic process during the year.Principal component analysis revealed that elevation,groundwater level,total nitrogen,alkaline hydrolyzable nitrogen,and available phosphorus were the main factors influencing the functional traits and population size characteristics of Phragmites australis,Typha minima and Calamagrostis pseudophragmites grass.