Research On Vegetation Succession And Restoration Mechanism Of The Central Bars In Lijiang River

In recent years, vegetation degradation has been increasingly compounded in the Lijiang River basin and the ecological environment is severely damaged. Hence, it’s extremely urgent to solve the problem of vegetation recovery in the Lijiang River basin. This paper regarded central bars of the Lijiang River basin as the research object, studied relations between phytocenosis and soil of central bars, explored basic characteristics of different types of central bars in the Lijiang River basin,analyzed its evolutionary changes and inner drives, as well as the main factors impacting growth of different types of vegetations on central bars with a view to providing theoretical basis and technical reference for feasibility of vegetation recovery near the central bars, promotion of vegetation recovery and ecological restoration on central bars. Research achievements are as follows:(1) Based on the analysis of factor influencing environment of central bars, this paper chose vegetation biomass, relative elevation difference, gradient, gravel content, soil water content, soil organic content, area of central bar, soil available nitrogen, soil available potassium and soil PH value as indexes for categorizing central bars. Correlation analysis and principal component analysis were applied to select vegetation biomass, relative elevation difference, gradient and gravel content as main factors. Then clustering analysis was adopted to divide central bars into three types including herbal central bar, shrub-grass central bar and arbor-shrub-grass central bar.(2) Within the scope of research field, there are 86 kinds of plants on central bars of the Lijiang River basin which belong to 81 categories of 41 families, including 65 kinds of herbal plants,10 kinds of shrub plants and 11 kinds of arborous plants. Dominant species of herbal plants on the central bar are Bermuda grass, sedge, glechoma longituba and so forth; dominant species of shrub plants are Chinese ash, throatroot and so forth; dominant species of arbor are Chinese ash and mulberry. In terms of peripheral diversity for three kinds of central bars, the diversity of phytocenosis at the end of the bar and place far away from the drainage line is greater than at the beginning of the bar and on the right side of the bar (on the side of the drainage line). The soil sand content of all three types is greater than 60%. As evolutionary stages of central bars increase, sand content, soil bulk density and soil water content take on the trend of decreasing before increasing. Soil gravel content shows a downward trend. Soil PH value gradually gets smaller but they all intend to be a bit alkaline. Soil organic, total nitrogen, total phosphorus, total potassium and available phosphorus increase first and then decrease. Available nitrogen decreases first and then increases while available potassium gradually increases.(3)A study on vegetation degradation of central bars of the Lijiang River basin shows:herbal central bar is on a stage of positive succession with dominant species of annual herb and herbaceos perennial. Shrub-grass central bar is on a stage of positive succession with dominant species of herbaceos perennial, shrub and low trees. The stability of plant community, communities diversity, evenness and abundance are all tended to increase while the niche breadth leveled off during vegetation degradation. Herbaceous plants on the central bars turn to ombrophyte from the drought and flood durable type. Central bar vegetation degradation process is herbal central bar→shrub-grass central bar→arbor-shrub-grass central bar. The main impetus for phytocenosis evolution of central bars in the Lijiang River basin is replacement of dominant species on central bars and adaptation of dominant species to hostile environment.(4) Flood is a main interference factor of central bars. Before the flood season, vegetation family, category, species and biomass all show an upward trend while there’s no obvious difference in diversity, dominance and balance before and after the flood season. Flood has the greatest impact on physical and chemical properties of soil in herbal central bars and the least impact on arbor-shrub-grass central bars. Prominent difference exists in soil bulk density, soil organic matter, total nitrogen, total phosphorus and PH value of herbal central bars before and after the flood season. Changes only take place in soil water content, soil bulk density and PH value of shrub-grass central bars while no obvious difference can be seen in factors of arbor-shrub-grass central bars except PH value.(5) Factors impacting vegetation of herbal central bars are flood, soil, terrain and man-made interference. Its vegetation restoration model is sowing of dominant species and transplant accompanied by slope protection projects. Factors influencing vegetation of shrub-grass central bars are flood, Available K, Available N soil organic matter, soil total nitrogen, relative elevation difference and man-made interference, and its vegetation restoration model is transplant of dominant species accompanied by slope protection projects. Factors influencing vegetation of arbor-shrub-grass central bars are flood, soil organic matter, slope,relative elevation difference and man-made interference, and its vegetation restoration model centers on natural restoration with after-culturing of vegetation and dry-laid pebble protection as auxiliary initiatives, which provides a feasible paradigm for the configuration of biological engineering measures during central bar ecological restoration.