A common soil temperature threshold for the upper limit of alpine grasslands in European mountains

Abstract While climatic research about treeline has a long history, the conditions corresponding to upper limit of closed alpine grasslands remain poorly understood. Here, we propose definition for this limit, ‘grassline’, in analogy treeline, which is based on growing season length and soil temperature. Eighty-seven mountain summits across ten European ranges, covering three biomes (boreal, temperate, Mediterranean), were inventoried as part GLORIA project. Vascular plant cover was estimated visually 326 plots 1 × m. Soil temperatures measured situ 2–7 years, from mean temperature derived. The 40% defined thresholds grassland. Closed vegetation present locations with warmer than 4.9 °C, or minimal 85 days, encompassing days daily ? °C. Hence, associated close that previously observed at accordance physiological growth vascular plants. In contrast trees, whose canopy coupled air temperature, small-stature plants benefit warmed by solar radiation consequently, they can grow higher elevations. Since substrate stability necessary occur their grassline rarely appears distinct linear feature.