Analysis of Invasive Weed Species Composition and Altitudinal Distribution in Farmland Ecosystems of Southern Zhejiang Mountainous Areas: A Case Study of Songyang County, Lishui

Based on field surveys of farmland ecosystems in Songyang County, Zhejiang Province, this study investigated the species composition, altitudinal distribution patterns, and habitat preferences of invasive weeds. The results showed that a total of 10 invasive weed species belonging to 7 families were recorded, with Asteraceae being the most represented family（4 species）, accounting for 40.0% of the total species. Invasion intensity（mean coverage）exhibited a declining trend with increasing altitude. The mean coverage in the low-altitude group（＜150 m）was 64.5%±22.0%（n=9）, higher than that in the mid-altitude group（150–250 m, 48.0%±15.2%, n=8）and the high-altitude group（＞250 m, 34.7%±9.0%, n=3）, with the Kruskal-Wallis test showing marginal significance（H=5.95, P=0.051）. Chi-square test indicated a significant correlation between species distribution and altitude（χ²=34.49, P=0.011）. Ageratum conyzoides was exclusively distributed in high-altitude areas, while Eichhornia crassipes was concentrated in mid-altitude areas. These findings provide a reference for early warning monitoring and classified management of invasive weeds in the mountainous regions of southern Zhejiang.