Poisonous weed species and their harmfulness in the grassland of

The general and random survey was conducted to identify the poisonous weed species during 2003 to 2009 in the native grassland of Yili regions, Xinjiang province. The survey results showed that there were 104 species of poisonous weeds belonging to 12 families, and these poisonous weeds covered 7.3105 hm2, and distributing the whole grassland of YiLi valley. The serious poisonous weeds were Aconitum leucostomum, A.soongoricun, Ligularia narynensis, Stellera chamaejasme, Leonurus heterophyllus, Sophora alopecuroides, Stipa capillata, Geum aleppicum, Eupborbia sp., Cirsium japonicum and Peganum harmalal. The dominant species are A. leucostamum，A.soongoricum and L.narynensis. The dominant plants were A.leucostamum, A.soongoricum and L.narynensis. The number of L.narynensis in the 100 m2 plot was 210 plants in 2003, 1 045 plants in 2006 and 2 347 plants in 2008, and that of A.leucostamum was 48 plants in 2003, 288 plants in 2006, 366 plants in 2008. This study implied that grassland areas of poisonous weed invasion increased quickly and covered the whole Yili valley, and these poisonous weeds germinated early, grew fast and had many reproductive and disperse ways, resulting in severe harmfulness to native grassland.