Distribution area
The distribution areas of A. artemisiifolia and A. trifidain the Yili Valley were surveyed and measured during the growth periods from 2010 to 2017. Every year, through a large number of field censuses, new distributional points of the two species were recorded with GPS to determine the current distribution boundaries of the two species. In order to ensure the accuracy of the measurements, we included a sufficient number of boundary points, with the distances between two consecutive points limited to 2–3 km. These points were then marked on a Google map to calculate the distribution areas.