2.1. Study Area

The study area is located in Wuqing District, Tianjin, China (117°18′ E, 39°22′ N), and has a warm temperate subhumid continental monsoon climate. The average annual temperature is 11.6 °C, the average temperature in January is −5.1 °C, the average temperature in July is 26.1 °C, the average annual precipitation is 606 mm, the frost-free period is 212 days and the annual sunshine duration is 2752 h. D. stramonium is an annual herb, and the annual new seedlings are reproduced by seeds. The experimental areas are three habitats invaded by D. stramonium, including farmland (FL), wasteland (WL) and roadside (RS). D. stramonium mainly invades farmland and wasteland and has a strong environmental adaptability and potential for invasion. There are more disturbances at the roadside compared to farmland and wasteland. The three habitats are more representative. In order to ensure that the elevation, precipitation and temperature of the three habitats are similar, the distance between the study areas of different habitats is not more than 10km. No prevention measures have been carried out in the experimental area in the past five years, and there is no human interference. D. stramonium has heavily invaded each study area; that is, D. stramonium was the dominant population in the community, and its cover was more than 60%. Each habitat was divided into two sample plots according to whether there was an invasion of D. stramonium: (1) Noninvaded area, that is, there is no D. stramonium in the sample plot and only native plants grow. (2) Invaded area, that is, there are D. stramonium and native plants growing in the sample plot, and the D. stramonium covers was more than 60%. The interval between the noninvaded and invaded area under the same habitat did not exceed 50 m to ensure the basic consistency of other conditions except vegetation factors.