Invasion patterns of seven alien plant species along roadsides in southern mountainous areas of Yunnan Province.
Roads serve multiple functions that enhance exotic species invasion. In this paper, we examined the roles of disturbance, light availability, slope aspect, and climate in explaining density and frequency of exotic invasive plants. We analyzed the effect of main environmental factors along 13 roads with different levels of anthropological disturbances (heavy, moderate, and light) in the north tropical and south subtropical mountainous zones in Yunnan Province. The results demonstrated that density of four species, Eupatorium adenophorum, E. odoratum, Ageratum conyzoides and Tithonia diversifoli, and frequency of E. adenophorum were significantly associated with distance from roads. The curves of these four alien plants all presented a single-peak pattern, and their maximum abundance occurred within 4 m of roads. These four alien plants invaded native plant communities from primary colonization points along road margins. Density of E. adenophorum, E. odoratum, A. conyzoides, T. diversifoli and Synedrella nodiflora and frequency of E. adenophorum, E. odoratum, A. conyzoides and T. diversifoli tended to be significantly higher along highly disturbed roads than moderately and lightly disturbed roads, indicating that plant communities adjacent to highly disturbed roads might be more prone to invasion. Density of E. adenophorum, E. odoratum and A. conyzoides and frequency of E. adenophorum, A. conyzoides and S. nodiflora were significantly higher in areas with high light level than those that had medium or low light levels. E. adenophorum, E. odoratum and A. conyzoides might obviously invade farther in habitats along roads that had high light level. Density of E. adenophorum, A. conyzoides and S. nodiflora were significantly higher on warm aspects than on cool aspects. E. adenophorum and T. diversifoli were mainly distributed in the south subtropical mountainous zones, while E. odoratum and S. nodiflora were mainly in the north tropical mountainous zones. A. conyzoides and Malvastrum coromandelianum were distributed in both zones. Tridax procumbens were very few along roadsides, which had no statistical significance. Management of roadside habitats should be considered a key to preventing and controlling alien plant invasion, and the maintenance of a dense canopy of native vegetation would benefit control of alien invasive plants.