| The Yellow River runs through 21 countries of Henan province, and the Henan province section is one of the important sections of the Yellow River watershed, this area is the source of Chinese civilization, also it is China's important grain production area. This area, from plain to hills and mountain, for invasive species provides a variety of habitat conditions to invade. Our Country has 188 kinds of alien invasive plants, and 49 kinds of them belongs to composite. In this area we found 6 kinds of alien invasive plants of composite: Conyza canadensis, Aster subulatus, Bidens pilosa, Conyza sumatrensis, Convza bonariensis, Erigeron annuus. In this area we selected 29 sites. At each site we choosed four habitats: riparian land, farmland, woodland, derelict land. At each habitat we set an area of 20m×20m, and at each plot we sampled 5 points of 1m×1m. Then we measure measured the height, the leaf length, the leaf breadth, the stem diameter, the number of leaves, flowers and seeds etc. of each invasive species plant.The result of our survey in spring,summer and fall of 2010 shows: in this area, C. canadensis is widely distributed; A.subulatus, C. sumatrensis and C. bonariensis mainly distribute in riparian land and woodland; B. pilosa mainly distribute in riparian land. In this area, the most harmful species is C. canadensis, followed by A. subulatus, B. pilosa which mainly damage the wetland landscape.According to observation and relevant information, we can estimate roughly the spread path and mode of transmission of C. canadensis and A. subulatus in this area. In 1860 C. canadensis was found at Shandong yantai, then in 1886 and 1887 we had picked C. canadensis at Hubei yichang and Sichuan naxi. So C. canadensis was probably introduced from Shandong to Henan, or from Sichuan to Shanxi. C. canadensis was via land or water or natural spread to the Yellow River, then C. canadensis spread to various habitats of the shoreside via transportation or interference by human irrigation. A. subulatus in 1947 was reported in Hubei wuchang, then it was introduced from wuhan to zhengzhou by natural spread or the dense network of railway and highway, then it spread to Henan section of the Yellow River Watershed.In plain C. canadensis was distributed widely, so it shows that the plain fits for its spread. With the rise of elevation and the decrease of temperature, each index of C. canadensis which grow in riparian land decline. C. canadensis's index which grows at the edge of the farmland shows no apparent change rule. Maybe because there is strong human interference. C. canadensis`s index which grows at the plantation and the derelict land has reached the peak in the hilly region. This may due to reasons such as air humidity and temperature. All of the above show that in Henan section of the Yellow River Watershed C. canadensis is suit to the environmental of the hilly region.In Different season, C. canadensis have different structure characteristics. From spring to autumn, it's height and stem diameter turn out to be higher. In summer, the leaf area is decrescent, and the blade thickness is thicker than in spring. That because C. canadensis is suit to the high temperature in summer, and the leaf number is maximal. In summer there is a small part of C. canadensis enter into the breeding season, but most of them enter into the breeding season in autumn. In order to adapt to the climate of this area, the weed can regulate it's growth itself, especially the characters of the leaf, so C. canadensis own strong adaptability.According to the observation of the experiment and peripheral environment and based on the inquiry to local villagers, we defined the degree of disturbance of these four habitat: the edge of farmland > derelict land > woodland > riparian land. The index of this weed which grow at the edge of the farmland and the derelict land are higher than the weed which grow at riparian lamd and woodland. Because of the different conditions of the habitats and different seasons and index, the index of the weed which grow at riparian lamd and woodland are different. Therefore, the conclusion is that strongger the interference becomes , higher the index will be. So we can conclude that C. canadensis can adapt strong interference within a certain interference domain.A. subulatus'index have the same rule with C. canadensis in this area. But there is some differences abut the index in different season. Because of the characteristics of A. subulatus'leaf, from spring to autumn the leaf area is larger and larger. In addition to woodland, A. subulatus also own the same rule about the adaptation to interference strength. So A. subulatus which grow at woodland need more sunlight.In this area, B. pilosa mainly distribute in riparian land, so it often harms the landscape of the wetland. C. sumatrensis mainly distribute in the downstream, and mainly grow at riparian land and the derelict land. C. bonariensis mainly distribute in the downstream but its number is low, and it mainly grow at riparian lamd and woodland. So in Henan section of the Yellow River Watershed C. sumatrensis and C. bonariensis are suit to the environmental of the plain region. The Henan section of the Yellow River Watershed is a region provides a continuous environment gradients. C. canadensis adapt the complex change of the environment gradients by regulating the distribution of the nutrition in different organs.The research in the background of the agricultural ecological system in Henan province section of the Yellow River Watershed is very important. It could help us find the balance between the invasion of the alien species and agricultural development. It also could provide conference for the comprehensive analysis of the invasion alien species at a larger scale. In addition, our research could provide help to prevent the outbreak of the invasion alien species in Henan section of the Yellow River Watershed.
|
PDF Full Text Request