Invasive Characteristics And Spreading Risk Of Solidago Canadensis In City Peripheral

In recent years, alien species invasion has become an increasingly serious ecological environmental problem. The invasion of alien species not only can be a threat to biodiversity, but also may damage the ecological environment, causing huge economic loses.Solodago canadensis (Canada goldnrod), a rhizomatous perennial plant (family, Compositae) originating from North America, was introduced into Nanjing, Shanghai and other places as a horticultural plant in1930s. After escaping the field has become a typical alien invasive species in eastern China. Thus the species was listed as one of the harmful alien plants in China. With high reproductive capacity and potential of rapid spread, this exotic plant has been changing the constitution of plant communities and diminishing biodiversity and soil utility. This species has invaded and caused serious damage to agricultural production and ecosystms in several provinces of China. Solidago canadensis has not only a strong resistance but also wide ecological amplitude, it can reproduce either sexually or asexually. In the process of invasion, Solidago canadensis can form numerous "satellite model" populations initially and then produce clones of individual plants with the aid of the underground rhizomes to fill the spatial gaps. It may eventually form a single dominant species population supplanting the native species. Meanwhile, the stems, leaves and underground rhizomes of Solidago canadensis can produce allelochemicals that may strongly inhibit the normal growth of other plants and eventually form a single population by crowding other plants out their birth environment. What is more, it also affects the yield and quality of crops, causing the city green belt area to yellow death. For decades, lots of researches on the physiological and ecological adaptability, allelopathy effects, genetic mutaion of Solidago Canadensis have been documented, but less attention has been paid to the invasive feature around a city.In this study, taking Wuhan as an example, we compared the invasion of Solidago canadensis with that of Conyza canadensis. Results show that both the allelepathy and reproductive capacity of Solidago canadensis are stronger than that of Conyza canadensis. Furthermore, Solidago canadensis is more difficult to wipe out in the distribution area. After a systematic survey of Solidago canadensis in Wuhan, we find that local habitats can be divided into4types according to differences in distribution and growth potential: Dongtoucun type, Zhiwuyuanlu type, Tuanshanlu type, Lumolu type. Through observation of a growth cycle of Solidago canadensis in4monitoring sites, we study its invasion characteristics in Wuhan surrounding. By using sample density method, we calculate the variation coefficients of individual S.canadensis populations at the4monitoring sites of Solidago by which the distribution characteristics are identified. The correlation between soil conditions and S. canadensis growth is analyzed by the method of principal component analysis (PCA). In accordance with the standard set by UN Food and Agriculture Organization (FAO), International Plant Protection Convention (IPPC), Chinese government on pest risk analysis (PRA), and combined with the characteristics of Solodogo canadensis around Wuhan, we construct the risk analysis index system and an evaluation model for Solidago canadensis in Wuhan. Based on indexes on pest distribution, potential harm, spreading possibility and risk management difficulty etc., both a qualitative and quantitative analysis about the invasive risk of Solidago canadensis in Wuhan are conducted. The main results are as follows:1. Solidago canadensis is still spreading in Wuhan. Since2005-, a large number of scattered Solidago canadensis plots have been spotted. The species was included in the "Hubei province forestry harmful biological supplement list" by province forestry bureau of Hubei in2006. At the same time, they organize relevant personnel to clear Solidago canandensis in flowering stage in October every year. The ground parts of Solidago canandensis are eliminated. However, rhizomatous root part was not thoroughly cleaned, and therefore the plants bud again next spring. In addition, lots of new distribution areas are found constantly in the places where there is no Solidago canadensis.2. Solidago canadensis at monitoring sits is highly clumped. Through setting the40quadrats to get species density, we ultimately calculate the distribution variation coefficients for individual populations at the4monitoring points of Solidago canadensis. Results show that the distribution deviates significantly from the pine and cypress, they are highly clumped. Through the investigation in Wuhan, we find that Solidago canadensis also tends to cluster in other distribution areas which is more conductive to its invasion.3. Solidago canadensis grows well in the high content of organic matter, good water conditions of alkaline soil. Water has become an important factor restricting its normal growth. Drought and high temperature weather in August have a serious impact on the growth of Solidago canadensis. Parts of the energy in the stems and leaves supplies to underground rhizomea. In September after the rain, the energy in stems and root quickly transferred to the sexual reproductive organs in order to blossom and seed dispersal. Principal component analysis was performed on soil index for the4monitoring sites. Results show that the soil sample that is most suitable for the growth of Solidago canadensis is Dongtoucun soil sample, the other3monitoring points of soil fertility is next to Dongtoucun. However, the plant biomass is not the highest in Dongtoucun, due to possible water shortage, which is not considered in the principle component analysis.4. Solidago canadensis distributed in Wuhan belongs to the highly dangerous pest. By reviewing the relevant literature and field investigation, we have analyzed the relevant situation of Solidago canadensis in Wuhan. Using the PAR index system and the evaluation model of risk analysis method, quantitative analyses are performed by using the PRA method. Based on the model we obtain the Solidago canadensis risk comprehensive evaluation value R being equal to2.35. According to this number, Solidago canadensis in Wuhan belongs to the highly dangerous, which has the great potential to spread.