Study site and plot establishment
We conducted our survey along an elevational gradient ranging from 3200 m to 4000 m a.s.l. on the south slope of the Qilian Mountains in Menyuan County, located on the northeastern Qinghai-Tibetan Plateau in China (Fig. S1.1). The region has a continental monsoon climate, with a 6-month growing season from mid-April to mid-October. The study took place in alpine meadow habitat, dominated by some perennial herbaceous genera (e.g. Gentiana , Kobresia , Poa andSaussurea ), with the species composition shifting with elevation. We established thirty 0.5 × 0.5 m plots (6 replicates for each of five elevations) along the elevational gradient at 3200 m (37°36’39” N, 101°18’16” E), 3400 m (37°39’58” N, 101°20’20” E), 3600 m (37°41’47” N, 101°21’34” E), 3800 m (37°42’13” N, 101°22’14” E) and 4000 m (37°42’29” N, 101°22’27” E). We randomly placed the plots with at least a 10 m buffer zone between two adjacent plots at each elevation.