Study On Plant Community Structure And Spatial Pattern Of Chaobai River Wetland In Beijing

Wetlands are known as the "kidneys of the earth" because of their important role in the ecological environment.Beijing’s Chaobai River wetlands flow through the eastern and northern parts of the city.However,in recent decades,the wetlands have been affected by urbanization and agricultural pollution due to the increase of human activities.Therefore,in this study,the Chaobai River wetlands in Beijing was investigated to collect the plant communities data and collect soil and water samples,and finally a total of 94 sample lines were investigated.Based on remote sensing images,land use data around the wetlands were obtained.Finally,based on the theory of plant community structure and spatial pattern,we found factors which impact on plant community,in order to provide a theoretical basis for the environmental management of the Chaobai River wetland in Beijing.The main research results are as follows:(1)There are 70 families,217 genera and 338 species of wetland plants in the Chaobai River wetlands in Beijing.There are 104 species of aquatic plants and 234 species of terrestrial plants.The plant structure of the wetlands in the Chaobai River wetlands is simple,mainly herbaceous plants.The geographic composition of the flora of families and genera is mainly of the world widespread type.Families are divided into6 range types and 3 subtypes.Genera are divided into 14 range types and 5 subtypes.(2)The wetland plants in the Chaobai River basin of Beijing are divided into 21 community types.The overall diversity of each plant community is low.The ShannonWiener diversity index of different communities varied from 1.138 to 2.438,and the Simpson diversity index fluctuated from 0.206 to 0.756.(3)There was a gradient distribution of plant diversity in both vertical and horizontal patterns in Chaobai River,Beijing.In the horizontal pattern,plant richness and plant abundance decreased significantly along the urbanization gradient;native species richness and native species abundance decreased significantly along the urbanization gradient;terrestrial plant richness decreased significantly with increasing urbanization level.In the vertical pattern,aquatic plant richness decreased with increasing elevation.The overall plant and native species plant richness increased with increasing elevation.Aquatic plant richness and terrestrial plant richness show opposite trends in the vertical pattern.(4)The distribution of plant communities in the Chaobai River wetlands in Beijing is influenced by elevation,the physicochemical properties of water and soil,the level of urbanization,and the surrounding land use.Human activities directly and indirectly affect the distribution of plant communities in the Chaobai River wetlands.Urbanization reduces the area of woodland and green space in wetlands,directly changing the wetland habitat and slightly affecting the species composition of wetland plant communities.As the area of cultivated land and construction land continues to expand,pollutants infiltrate into the river and the nutrient level of the wetland changes,thus indirectly changing the distribution of plant communities.(5)The wetland area of the Chaobai River is the most important factor affecting plant diversity,and plant richness and abundance decrease with the decrease in wetland area.The reduction of native species is influenced by cultivated area which indirectly promoted the growth and spread of native species by increasing the total organic carbon content of water,but the impact is much less than the direct damage by agricultural activities.Erosion of wetlands by woodlands significantly reduced native species abundance.The effects of soil p H,water p H,soil organic matter and slope on introduced species showed opposite trends on native species.Introduced species are significantly more adapted to land use around wetlands than native species,and green areas as well as woodlands could promote the spread of introduced species,but are significantly less adapted to the physicochemical properties of soils and water in urban wetlands than native species.The impact of human activities leading to a decrease of native species in the wetland;and through agricultural cultivation,it leads to the escape of invasive species from cultivated land into the wetland,resulting in an increase of introduced species.The length of the riparian shows opposite effects on the diversity of aquatic as well as terrestrial plants.Pollution from urbanization and agriculture has both positive and negative effects on aquatic plants.Aquatic plants respond better to nutrients in the water than they do to soil nutrients and terrestrial plants respond to soil nutrients.Terrestrial plants are more resistant than aquatic plants to pollution from urbanization and agricultural activities,and to encroachment of wetlands by forest and cropland.