Species diversity patterns in <i>Tagetes minuta</i> -invaded plant communities along an elevational gradient in Southeastern Xizang

<i>Tagetes minuta</i>, a herbaceous plant native to South America, has shown a significant trend of invasion along the section from Nyingchi to Shannan, situated along the Yarlung Zangbo River in southeastern Xizang in recent years. In this study, we conducted field surveys of <i>T. minuta</i> plant communities at elevations ranging from 2,925 to 3,553 m. By establishing 31 quadrats, we systematically analyzed the species composition, diversity characteristics of the invaded communities of <i>T. minuta</i>, and their relationships with elevation gradients and habitat types. The study results revealed that a total of 78 plant species, belonging to 28 families and 69 genera, were recorded in the <i>T. minuta</i>-invaded plant communities. Among them, the families Asteraceae, Poaceae, and Rosaceae were dominant, with herbaceous plants being in an absolute majority. The diversity analysis showed that the Shannon-Wiener index, Simpson index, and Pielou's evenness index of were significantly higher in the community group mainly composed of <i>Eragrotis pilosa</i> and <i>Plantago depressa</i> (Cluster Group II) compared to the groups dominated by <i>Poa annua</i> plus <i>Plantago depressa</i> (Cluster Group I) and <i>Poa annua</i> and <i>Digitaria cruciata</i> (Cluster group III) (<i>P</i> < 0.05), while no significant differences were found in species richness. This suggests that the invasion of <i>T. minuta</i> primarily affects the evenness of species distribution rather than species richness. In addition, the species diversity indices of the <i>T. minuta</i>-invaded plant communities showed no significant correlation with elevation, indicating that elevation is not a major factor influencing species diversity in the invaded communities. The height of <i>T. minuta</i> was significantly positively correlated with elevation (<i>P</i> < 0.01), while its cover showed no significant correlation with elevation. Under different habitat types, the height and cover of <i>T. minuta</i> showed significant differences, with stronger invasion ability in habitats with greater human disturbance. This study highlights the invasion characteristics of <i>T. minuta</i> and its relationship with elevation in southeastern Xizang, offering valuable data for the ecological management of invasive plant species in plateau regions.