Expanding processes of alien invasive plant species play an important role in determining their distribution. These processes are affected by various factors in the invaded communities. Tithonia diversifolia, as one of the most serious invasive plant species in Yunnan Province, has attracted attention from ecology, agriculture, and the environment. To answer the relationships between population- and individual-level characteristics of T. diversifolia and habitat types, we conducted an investigation and an experiment. We surveyed the exotic′s relative cover, relative density and height in the communities dominated by T. diversifolia (H1), T. diversifolia and Chromolaena odorata (H2), and T. diversifolia and Ageratina adenophora (H3), respectively, using ten 1×1 m2 plots per habitat. The relative cover and relative density of T. diversifolia were significantly higher in the H1 than in the H2 and H3; the height of T. diversifolia was significantly higher in the H1 than in the H3, but not in the H2; H2 and H3 exhibited similar relative cover, relative density, and height.
A field experiment was conducted to identify individual-level responses of T. diversifolia to microclimate, soils, and competition, each with two levels (i.e., shrubland microclimate and grassland microclimate, shrubland soil and grassland soil, and with and without competition). There were ten replicates for each combination. A dominant native species Neyraudia reynaudiana was chosen to compare its responses with ones of T. diversifolia. We created growth containers, changed the soils, and transplanted experimental seedlings. At the end of this experiment, we determined height and leaf number of T. diversifolia and N. reynaudiana. The interactions of microclimate, soils and competition significantly affected the height, but not number of leaves of T. diversifolia, and the height and number of leaves of T. diversifolia did not respond to microclimate, soils, and competition alone. There were some differences in individual responses between T. diversifolia and N. reynaudiana. These findings are showing that multiple factors determine the habitat association of T. diversifolia.