DOI: 10.1111/j.1466-8238.2009.00460.x © 2009 Blackwell Publishing Ltd www.blackwellpublishing.com/geb 473 Global Ecology and Biogeography, (Global Ecol. Biogeogr.) (2009) 18, 473– 484 RESEARCH PAPER Blackwell Publishing Ltd Changes in the onset of spring growth in shrubland species in response to experimental warming along a north–south gradient in Europe Patricia Prieto 1 , Josep Peñuelas 1 *, Ülo Niinemets 2 , Romà Ogaya 1 , Inger K. Schmidt 3 , Claus Beier 4 , Albert Tietema 5 , Alwyn Sowerby 6 , Bridget A. Emmett 6 , Edit Kovács Láng 7 , György Kröel-Dulay 7 , Barbara Lhotsky 7 , Carla Cesaraccio 8 , Grazia Pellizzaro 8 , Giovanbattista de Dato 9 , Costantino Sirca 10 and Marc Estiarte 1 ABSTRACT Aim To test whether the onset of spring growth in European shrublands is advanced in response to the warmer conditions projected for the next two decades by climate models, and, if there is a change, whether it differs across Europe. Location The studied sites spanned a broad north–south European gradient with average annual temperatures (8.2–15.6 °C) and precipitation (511–1427 mm). Methods ‘Bud break’ was monitored in eight shrub and grass species in six European sites under control and experimentally warmer conditions generated by automatic roofs covering vegetation during the night. Results Species responsive to increased temperatures were Vaccinium myrtillus and Empetrum nigrum in Wales, Deschampsia flexuosa in Denmark, Calluna vulgaris in Netherlands, Populus alba in Hungary and Erica multiflora in Spain. Although the acceleration of spring growth was the commonest response to warming treat- ments, the responses at each site were species specific and year dependent. Under experimental warming 25% of cases exhibited a significantly earlier onset of the growing season and 10% had a significantly delayed onset of vegetative growth. No geographical gradient was detected in the experimental warming effects. However, there was a trend towards a greater dominance of phenological advances with more intense the warming treatments. Above 0.8 °C warming, only advancements were recorded. Main conclusions Our results show that warmer temperatures projected for the next decades have substantial potential effects on the phenology of the spring growth of dominant species in different European shrublands, with a dominant trend towards advancements the more intense the warming is. However, our study also demonstrates the overall difficulties of applying simple predictive relationships to extrapolate the effects of global change on phenology. Various combinations of environmental factors occur concurrently at different European sites and the interactions between different drivers (e.g. water and chilling) can alter phenology significantly. Keywords Bud break, climate warming, European gradient, experimental warming, phenology, shrubland, spring growth. *Correspondence: Josep Peñuelas, Unitat Ecofisiologia i Canvi Global CSIC-CEAB- CREAF, CREAF (Centre de Recerca Ecològica i Aplicacions Forestals), Edifici C, Universitat Autònoma de Barcelona, 08193 Bellaterra, Barcelona, Spain. E-mail: josep.penuelas@uab.cat 1 Unitat d’Ecofisiologia i Canvi Global CREAF- CEAB-CSIC (Centre for Ecological Research and Forestry Applications), Universitat Autònoma de Barcelona, Edifici C, 08193 Bellaterra, Spain, 2 Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences, Kreutzwaldi 1, Tartu 51014, Estonia, 3 Forest and Landscape, Denmark, University of Copenhagen, Hørsholm Kongevej 11, DK-2970 Hørsholm, Denmark, 4 RISØ National Laboratory, PO Box 49, DK-4000 Roskilde, Denmark, 5 Center for Geo-ecological Research (ICG), Institute for Biodiversity and Ecosystem Dynamics (IBED), University of Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands, 6 Centre for Ecology and Hydrology–Bangor, Deiniol Road, Bangor, Gwynedd LL57 2UP, UK, 7 Institute of Ecology and Botany, Hungarian Academy of Sciences, H-2163 Vácrátót, Hungary, 8 National Research Council of Italy, Institute of Biometeorology (CNR-IBIMET), Via Funtana di lu Colbu 4/A, 07100 – Sassari, Italy, 9 Department of Forest Environment and Resources (DISAFRI), University of Tuscia, Via San Camillo de Lellis, I-01100 Viterbo, Italy, 10 Department of Economics and Tree Crops (DESA), University of Sassari, Via Enrico De Nicola 1, 07100 Sassari, Italy.