Abstract:Climate warming may threaten the survival of alpine cushion plants, which may have great implications for the stability of alpine ecosystems. However, little research has investigated the climatic causes of the altitudinal distribution of cushion plants. We hypothesize that for a widespread cushion species in semi-arid regions, there is a unimodal pattern of plant cover associated with an optimum combination of temperature and precipitation. We conducted a livestock exclosure experiment across the upper (5300 m) and lower (4430 m) limits of a widespread cushion species (Androsace tapete) along the south-facing slope of the Nyaiqentanglha Mountains during the period 2006–2010. The plant cover and survival across the fenced and unfenced quadrats were observed near weather stations at eight altitudes. There was a unimodal pattern in the coverage of A. tapete along the experimental gradient, which was confirmed by additional data from other species and mountains in this region. The coverage showed quadratic relationships with mean temperatures and the ratio of growing-season precipitation to the ≥5 °C accumulated temperature sum. Five-year monitoring data under fenced conditions demonstrated that the annual survival of A. tapete decreased away from the optimum distribution center. The results supported the hypothesis, suggesting a shift in the limiting factors of plant distribution between low and high altitudes.
