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

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

Accelerated increase in plant species richness on mountain summits is linked to warming

We thank D. Barolin, J. Birks, A. Björken, C. Björken, S. Dahle, U. Deppe, G. Dussassois, J. V. Ferrández, T. Gassner, S. Giovanettina, F. Giuntoli, Ø. Lunde Heggebø, K. Herz, A. Jost, K. Kallnik, W. Kapfer, T. Kronstad, H. Laukeland, S. Nießner, M. Olson, P. Roux-Fouillet, K. Schofield, M. Suen, D. Watson, J. Wells Abbott, J. Zaremba and numerous additional helpers for fieldwork support; P. Barancˇ ok, J. L. Benito Alonso, M. Camenisch, G. Coldea, J. Dick, M. Gottfried, G. Grabherr, J. I. Holten, J. Kollár, P. Larsson, M. Mallaun, O. Michelsen, U. Molau, M. Pus¸  cas¸ , T. Scheurer, P. Unterluggauer, L. Villar, G.-R. Walther, and numerous helpers for data originating from the GLORIA network13; C. Jenks for linguistic support; and the following institutions for funding. M.J.S.: Danish Carlsbergfondet (CF14-0148), EU Marie Sklodowska-Curie action (grant 707491). C.R., V.S., S.W.: Velux Foundation, Switzerland. C.R., V.S., S.W., J.-P.T., P.V.: Swiss Federal Office for the Environment (FOEN). A.K.: Swiss National Science Foundation (31003A_144011 to C.R.), Basler Stiftung für biologische Forschung, Switzerland. J.K.: Fram Centre, Norway (362202). J.K., J.-A.G., P.C., B.J.: Polish-Norwegian Research Programme of the Norwegian National Centre for Research and Development (Pol-Nor/196829/87/2013). O.F.-A., M.J.H., S.P.: Instituto de Estudios Altoaragoneses (Huesca, Spain). S.D.: Austrian Climate Research Programme (ACRP, project 368575: DISEQU-ALP). F.J.: Botanical Society of Britain & Ireland; Alpine Garden Society, UK. M.J.H.: Felix de Azara research grant (IBERSUMIT project, DPH, Spain). R.K.: Slovak Research and Development Agency (APVV 0866-12). S.N., D.G.: VILLUM Foundation’s Young Investigator Programme (VKR023456; Denmark). S.P.: Ramón y Cajal fellowship (RYC-2013-14164, Ministerio de Economía y Competitividad, Spain). J.-C.S.: European Research Council (ERC-2012-StG-310886-HISTFUNC); VILLUM Investigator project (VILLUM FONDEN grant 16549; Denmark). S.W.: WSL internal grant (201307N0678, Switzerland); EU FP7 Interact Transnational Access (AlpFlor Europe). S.W., S.B., F.J., M.J.H.: Swiss Botanical Society Alpine Flower Fund. Time and effort was supported by sDiv, the Synthesis Centre of iDiv, Germany (DFG FZT 118, sUMMITDiv working group).Peer reviewedPostprin