The Influence Study Of Main Harmful Exotic Plants On The Characteristics Of Plants Community Of Changsha

Exotic plants have undoubtedly playered important roles in the city forestation and grassing. However, they have also brought serous problems for the protection of city ecology and environment. Based on the analyses of the scarcity and vulnerability of the vegetation system of Changsha, the influence of exotic plants to the city vegetation system, the mechanism of the structure transformation and regressive succession of city plant communities, the mechanism of decreasing of the diversity of species and ecosystems. Lastly, the mechanism of the founding and wild proliferation of exotic plant population is discussed considering the biological characteristics and adaptation capacity of exotic plants, as well as some environmental and artificial factors.The artificial interferences increasing makes species diversity rising first and dropping later in herb layer, but dropping first and rising later in shrub layer. It is show that the medium artificial interferences to be helpful for herb layer renewing, but unhelpful for shrub layer. As the influence of exotic plants enhancing, the species diversity rising first and dropping later in backcountry herb layer, dropping always in suburb herb layer, dropping first and rising later in city herb layer; The species diversity dropping first and rising later in backcountry shrub layer, dropping always in suburb shrub layer, and it is same to the city shrub layer. As the influence of exotic plants enhancing, the number of common species is rising in backcountry and suburb, but the number of coexisting species is dropping in suburb and city. As the influence of exotic plants enhancing in three areas, the plants structure tends to simplificated and uncomplicated, and the rising and dropping number of species is down.As the influence of exotic plants enhancing, their Importment values are changing, their Importment values are minimum in backcountry, but are maximum in suburb, in this area the exotic gorwing well, and its influence is grave. The influence of exotic in herb is more grave than in shrub. The niche breadth decided by different the biological characteristics and adaptation capacity of exotic plants, as well as some environmental and artificial factors; The niche proportional similarity is dropping in backcountry, rising first and dropping later in suburb, and it is same in city. But dropping first and rising later from backcountry to city. The niche overlap is the same to the niche breadth.The influence of exotic plants have some relation to the plant patch, In backcountry the influence of exotic plants is maximum in punctual patch, medium in linear patch, and minimum in planar patch. In suburb, the influence of exotic plants is maximum in punctual patch and in linear patch, but minimum in planar patch. In city , the influence of exotic plants is medium in punctual patch and in linear patch, but maximum in planar patch.The exotic plants can induce the landscape structure changing, and landscape structure changing can influence the landscape function, As the influence of exotic plants enhancing, inbackcountry, it is unhelpful for animal action, but helpful first for plants action and unhelpful later; The speed of nutrient current is raising, and the same to the volum of nutrient; The soil current is raising too; The efficiency of energy transformers and the volum of energy are all dropping. In suburb, it is unhelpful for animal action and plant action ; The speed of nutrient current and volum of nutrient are raising; The soil current is raising; The efficiency of energy exchange is dropping but the volum of energy is unchangeable. In city, it is helpful for animal action and unhelpful for plant action; The speed of nutrient current is raising; but the volum of nutrient is dropping; The soil current is raising first and dropping later; The efficiency of energy exchange and volum of energy are all dropping.