Study systems
This study was conducted in the Himalaya-Hengduan Mountains (HHM) in SW China, where is one of the richest and most complex floras in the temperate zone of the Northern Hemisphere (Sun et al., 2017). See Text S1 for the details. Field experiments were conducted in northwestern Yunnan province (Figure S1), which is in the core area of alpine plant diversity of the HHM (Zhang et al., 2021). We selected eight communities dominated by the typical cushion plantArenaria polytrichoides Edgew. (Caryophyllaceae) as our study systems. As foundation species, A. polytrichoides plays key roles in the alpine ecosystem functions in this region (Text S2). Specifically, we selected four populations along an altitudinal gradient in Pujin pasture of the Baima Snow Mountains (Figure S1) to elucidate the cushion plant’s population dynamics, the associated plant diversity changes and the underlying mechanisms. In addition, another four populations in different mountain ranges were also selected to assess and compare current population dynamics at larger scale and predict potential biodiversity changes in alpine ecosystems more broadly (Figure S1). See Text S3 for the details.