How did Swiss forest trees respond to the hot summer 2015?

  • Susanne Burri
  • Elena Haeler
  • Werner Eugster
  • Matthias Haeni
  • Sophia Etzold
  • Lorenz Walthert
  • Sabine Braun
  • Roman Zweifel
Keywords: Climate change, tree growth, heat wave 2015, Swiss forests, point dendrometer, stem radius changes, Picea abies, Abies alba, Fagus sylvatica, Quercus spp


Central Europe experienced an exceptionally hot summer in 2015. The area of investigation in the Central Alps in Switzerland faced the second warmest summer since the beginning of measurements in 1864. As a consequence, agriculture suffered from considerable production losses. But how were forests affected by the hot summer? We analyzed stem growth data, measured by automated point dendrometers, from 50 trees across nine sites covering the four main Swiss tree species spruce (Picea abies), fir (Abies alba), beech (Fagus sylvatica) and oak (Quercus spp.) in the years 2014 (relatively wet and cool) and 2015 (hot and dry). Annual growth and environmental conditions were determined by, and related to, the growing period based on daily resolved growth data. Our multi-species approach revealed a wide range of responses. Radial growth of spruce was largely reduced during the hot summer 2015 for sites located below 1500 m a.s.l.. Growth of beech responded even positively at several sites on the Swiss Plateau. Fir and oak did not significantly deviate from their respective average growth rate. We conclude that one hot summer actually matters for stem growth, but its effect is not a priori negative. The timing of the heat wave is of highest importance. A relatively wet previous year, a wet spring and the relatively late occurrence of the heat wave in the wood growth period led to a less strong growth reduction than what could have been expected from agricultural plants. Endogenous effects like mast fruiting and legacy effects from past conditions are suggested to further play an important role for stem growth.


Anderegg, W.R.L., Schwalm, C., Biondi, F., Camarero, J.J., Koch, G., Litvak, M., Ogle, K., Shaw, J.D., Shevliakova, E., Williams, A.P., Wolf, A., Ziaco, E., and Pacala, S. (2015). Pervasive drought legacies in forest ecosystems and their implications for carbon cycle models. Science 349, 528-532. 10.1126/science.aab1833

Babst, F., Carrer, M., Poulter, B., Urbinati, C., Neuwirth, B., and Frank, D. (2012). 500 years of regional forest growth variability and links to climatic extreme events in Europe. Environmental Research Letters 7, 1-11. 10.1088/1748-9326/7/4/045705

Bayerische Landesanstalt Für Wald Und Forstwirtschaft (2016). "Trockensommer 2015", in: LWF aktuell. (Weihenstephan, Germany).

Braun, S., Schindler, C., and Rihm, B. (2017). Growth trends of beech and Norway spruce in Switzerland: The role of nitrogen deposition, ozone, mineral nutrition and climate. Science of the Total Environment 599, 637-646. 10.1016/j.scitotenv.2017.04.230

Bugmann, H., Brang, P., Elkin, C., Henne, P., Jakoby, O., Lévesque, M., Lischke, H., Psomas, A., Rigling, A., Wermerlinger, B., and Zimmermann, N.E. (2014). "Climate change impacts on tree species, forest properties and ecosystem services," in CH2014-Impacts, Toward Quantitative Scenarios of Climate Change Impacts in Switzerland, ed. F. Occr, Meteoswiss, C2sm, Agroscope, Procclim. (Bern, Switzerland), 136.

Bundesamt Für Umwelt, B. (2016). "Hitze und Trockenheit im Sommer 2015. Auswirkungen auf Mensch und Umwelt.". (Bern: Bundesamt für Umwelt, BAFU).

Ch2011 (2011). Swiss Climate Change Scenarios CH2011. Zurich, Switzerland: C2SM, MeteoSwiss, ETH, NCCR Climate, and OcCC.

Cook, B.I., Wolkovich, E.M., and Parmesan, C. (2012). Divergent responses to spring and winter warming drive community level flowering trends. Proceedings of the National Academy of Sciences of the United States of America 109, 9000-9005. 10.1073/pnas.1118364109

Cuny, H.E., Rathgeber, C.B.K., Frank, D., Fonti, P., Makinen, H., Prislan, P., Rossi, S., Del Castillo, E.M., Campelo, F., Vavrcik, H., Camarero, J.J., Bryukhanova, M.V., Jyske, T., Gricar, J., Gryc, V., De Luis, M., Vieira, J., Cufar, K., Kirdyanov, A.V., Oberhuber, W., Treml, V., Huang, J.-G., Li, X., Swidrak, I., Deslauriers, A., Liang, E., Nojd, P., Gruber, A., Nabais, C., Morin, H., Krause, C., King, G., and Fournier, M. (2015). Woody biomass production lags stem-girth increase by over one month in coniferous forests. Nature Plants 1, 1-6. 10.1038/nplants.2015.160

Dietrich, L., Delzon, S., Hoch, G., and Kamen, A. (2018). No role for xylem embolism or carbohydrate shortage in temperate trees during the severe 2015 drought. Journal of Ecology DOI: 10.1111/1365-2745.13051.

Feichtinger, L.M., Eilmann, B., Buchmann, N., and Rigling, A. (2014). Growth adjustments of conifers to drought and to century-long irrigation. Forest Ecology and Management 334, 96-105. 10.1016/j.foreco.2014.08.008

Gessler, A., Keitel, C., Kreuzwieser, J., Matyssek, R., Seiler, W., and Rennenberg, H. (2007). Potential risks for European beech (Fagus sylvatica L.) in a changing climate. Trees-Structure and Function 21, 1-11. 10.1007/s00468-006-0107-x

Granier, A., Reichstein, M., Breda, N., Janssens, I.A., Falge, E., Ciais, P., Grunwald, T., Aubinet, M., Berbigier, P., Bernhofer, C., Buchmann, N., Facini, O., Grassi, G., Heinesch, B., Ilvesniemi, H., Keronen, P., Knohl, A., Kostner, B., Lagergren, F., Lindroth, A., Longdoz, B., Loustau, D., Mateus, J., Montagnani, L., Nys, C., Moors, E., Papale, D., Peiffer, M., Pilegaard, K., Pita, G., Pumpanen, J., Rambal, S., Rebmann, C., Rodrigues, A., Seufert, G., Tenhunen, J., Vesala, I., and Wang, Q. (2007). Evidence for soil water control on carbon and water dynamics in European forests during the extremely dry year: 2003. Agricultural and Forest Meteorology 143, 123-145.

Greene, D.F., and Johnson, E.A. (1994). Estimating the mean annual seed production of trees. Ecology 75, 642-647. 10.2307/1941722

Gunderson, C.A., Edwards, N.T., Walker, A.V., O'hara, K.H., Campion, C.M., and Hanson, P.J. (2012). Forest phenology and a warmer climate - growing season extension in relation to climatic provenance. Global Change Biology 18, 2008-2025. 10.1111/j.1365-2486.2011.02632.x

Haeni, M., Zweifel, R., Eugster, W., Gessler, A., Zielis, S., Bernhofer, C., Carrara, A., Grunwald, T., Havrankova, K., Heinesch, B., Herbst, M., Ibrom, A., Knohl, A., Lagergren, F., Law, B.E., Marek, M., Matteucci, G., Mccaughey, J.H., Minerbi, S., Montagnani, L., Moors, E., Olejnik, J., Pavelka, M., Pilegaard, K., Pita, G., Rodrigues, A., Sanchez, M.J.S., Schelhaas, M.J., Urbaniak, M., Valentini, R., Varlagin, A., Vesala, T., Vincke, C., Wu, J., and Buchmann, N. (2017). Winter respiratory C losses provide explanatory power for net ecosystem productivity. Journal of Geophysical Research-Biogeosciences 122, 243-260. 10.1002/2016jg003455

Hartl-Meier, C., Dittmar, C., Zang, C., and Rothe, A. (2014). Mountain forest growth response to climate change in the Northern Limestone Alps. Trees 28, 819-829. 10.1007/s00468-014-0994-1

Hentschel, R., Hommel, R., Poschenrieder, W., Grote, R., Holst, J., Biernath, C., Gessler, A., and Priesack, E. (2016). Stomatal conductance and intrinsic water use efficiency in the drought year 2003: a case study of European beech. Trees-Structure and Function 30, 153-174. 10.1007/s00468-015-1284-2

Herrmann, V., Mcmahon, S.M., Detto, M., Lutz, J.A., Davies, S.J., Chang-Yang, C.H., and Anderson-Teixeira, K.J. (2016). Tree Circumference Dynamics in Four Forests Characterized Using Automated Dendrometer Bands. Plos One 11. 10.1371/journal.pone.0169020

Hinckley, T.M., Dougherty, P.M., Lassoie, J.P., Roberts, J.E., and Teskey, R.O. (1979). A severe drought: Impact on tree growth, phenology, net photosynthetic rate and water relations. American Midland Naturalist 102, 307-316.

Ionita, M., Tallaksen, L.M., Kingston, D.G., Stagge, J.H., Laaha, G., Van Lanen, H.a.J., Scholz, P., Chelcea, S.M., and Haslinger, K. (2017). The European 2015 drought from a climatological perspective. Hydrology and Earth System Sciences 21, 1397-1419. 10.5194/hess-21-1397-2017

Jolly, W.M., Dobbertin, M., Zimmermann, N.E., and Reichstein, M. (2005). Divergent vegetation growth responses to the 2003 heat wave in the Swiss Alps. Geophys. Research Letters 32.

Jucker, T., Grossiord, C., Bonal, D., Bouriaud, O., Gessler, A., and Coomes, D.A. (2017). Detecting the fingerprint of drought across Europe's forests: do carbon isotope ratios and stem growth rates tell similar stories? Forest Ecosystems 4, DOI 10.1186/s40663-40017-40111-40661. 10.1186/s40663-017-0111-1

Körner, C. (2012). Alpine treelines: functional ecology of the global high elevation tree limits. Basel: Springer.

Latte, N., Perin, J., Kint, V., Lebourgeois, F., and Claessens, H. (2016). Major Changes in Growth Rate and Growth Variability of Beech (Fagus sylvatica L.) Related to Soil Alteration and Climate Change in Belgium. Forests 7, 1-15. 10.3390/f7080174

Meteoswiss (2015a). "Klimabulletin Frühling 2015". (Zurich, Switzerland).

Meteoswiss (2015b). "Klimabulletin Sommer 2015". (Zurich, Switzerland).

Meteoswiss (2016). "Der Hitzesommer 2015 in der Schweiz", in: Fachbericht MeteoSchweiz. (Zurich, Switzerland).

Meteoswiss (2018). "Klimabulletin Sommer 2018". (Zürich, Switzerland).

Mullerova, J., Pejcha, V., Altman, J., Plener, T., Dorner, P., and Dolezal, J. (2016). Detecting Coppice Legacies from Tree Growth. Plos One 11. 10.1371/journal.pone.0147205

Muthers, S., Laschewski, G., and Matzarakis, A. (2017). The summers 2003 and 2015 in south-west Germany: Heat waves and heat-related mortality in the context of climate change. Atmosphere 8. 10.3390/atmos8110224

Nussbaumer, A., Waldner, P., Etzold, S., Gessler, A., Benham, S., Thomsen, I.M., Jorgensen, B.B., Timmermann, V., Verstraeten, A., Sioen, G., Rautio, P., Ukonmaanaho, L., Skudnik, M., Apuhtin, V., Braun, S., and Wauer, A. (2016). Patterns of mast fruiting of common beech, sessile and common oak, Norway spruce and Scots pine in Central and Northern Europe. Forest Ecology and Management 363, 237-251. 10.1016/j.foreco.2015.12.033

Ogle, K., Barber, J.J., Barron-Gafford, G.A., Bentley, L.P., Young, J.M., Huxman, T.E., Loik, M.E., and Tissue, D.T. (2015). Quantifying ecological memory in plant and ecosystem processes. Ecology Letters 18, 221-235. 10.1111/ele.12399

Pannatier, E.G., Dobbertin, M., Heim, A., Schmitt, M., Thimonier, A., Waldner, P., and Frey, B. (2012). Response of carbon fluxes to the 2003 heat wave and drought in three mature forests in Switzerland. Biogeochemistry 107, 295-317. 10.1007/s10533-010-9554-y

Pretzsch, H., Schutze, G., and Biber, P. (2018). Drought can favour the growth of small in relation to tall trees in mature stands of Norway spruce and European beech. Forest Ecosystems 5, 10.1186/s40663-40018-40139-x. 10.1186/s40663-018-0139-x

R Core Team (2016). R: A language and environment for statistical computing [Online]. R Foundation for Statistical Computing. Available: [Accessed].

Scherrer, S.C., Fischer, E.M., Posselt, R., Liniger, M.A., Croci-Maspoli, M., and Knutti, R. (2016). Emerging trends in heavy precipitation and hot temperature extremes in Switzerland. Journal of Geophysical Research-Atmospheres 121, 2626-2637. 10.1002/2015jd024634

Shao, J., Zhou, X., Luo, Y., Li, B., Aurela, M., Billesbach, D., Blanken, P.D., Bracho, R., Chen, J., Fischer, M., Fu, Y., Gu, L., Han, S., He, Y., Kolb, T., Li, Y., Nagy, Z., Niu, S., Oechel, W.C., Pinter, K., Shi, P., Suyker, A., Torn, M., Varlagin, A., Wang, H., Yan, J., Yu, G., and Zhang, J. (2016). Direct and indirect effects of climatic variations on the interannual variability in net ecosystem exchange across terrestrial ecosystems. Tellus Series B-Chemical and Physical Meteorology 68, 1-16. 10.3402/tellusb.v68.30575

Sterck, F., and Schieving, F. (2011). Modelling functional trait acclimation for trees of different height in a forest light gradient: emergent patterns driven by carbon gain maximization. Tree Physiology 31, 1024-1037. 10.1093/treephys/tpr065

Thomas, C.K., Law, B.E., Irvine, J., Martin, J.G., Pettijohn, J.C., and Davis, K.J. (2009). Seasonal hydrology explains interannual and seasonal variation in carbon and water exchange in a semiarid mature ponderosa pine forest in central Oregon. Journal of Geophysical Research-Biogeosciences 114, 1-22. 10.1029/2009jg001010

Van Der Maaten-Theunissen, M., Bummerstede, H., Iwanowski, J., Scharnweber, T., Wilmking, M., and Van Der Maaten, E. (2016). Drought sensitivity of beech on a shallow chalk soil in northeastern Germany - a comparative study. Forest Ecosystems 3. 10.1186/s40663-016-0083-6

Vanoni, M., Bugmann, H., Notzli, M., and Bigler, C. (2016). Quantifying the effects of drought on abrupt growth decreases of major tree species in Switzerland. Ecology and Evolution 6, 3555-3570. 10.1002/ece3.2146

Waller, D.M. (1979). Models of mastfruiting in trees. Journal of Theoretical Biology 80, 223-232. 10.1016/0022-5193(79)90207-8

Weemstra, M., Eilmann, B., Sass-Klaassen, U.G.W., and Sterck, F.J. (2013). Summer droughts limit tree growth across 10 temperate species on a productive forest site. Forest Ecology and Management 306, 142-149. 10.1016/j.foreco.2013.06.007

Wolf, S., Keenan, T.F., Fisher, J.B., Baldocchi, D.D., Desai, A.R., Richardson, A.D., Scott, R.L., Law, B.E., Litvak, M.E., Brunsell, N.A., Peters, W., and Van Der Laan-Luijkx, I.T. (2016). Warm spring reduced carbon cycle impact of the 2012 US summer drought. Proceedings of the National Academy of Sciences of the United States of America 113, 5880-5885. 10.1073/pnas.1519620113

Zielis, S., Etzold, S., Zweifel, R., Eugster, W., Haeni, M., and Buchmann, N. (2014). NEP of a Swiss subalpine forest is significantly driven not only by current but also by previous year’s weather. Biogeosciences 11, 1627-1635. doi:10.5194/bg-11-1627-2014

Zweifel, R. (2016). Radial stem variations - a source of tree physiological information not fully exploited yet. Plant, Cell and Environment 39, 231-232. doi: 10.1111/pce.12613

Zweifel, R., Eugster, W., Etzold, S., Dobbertin, M., Buchmann, N., and Häsler, R. (2010). Link between continuous stem radius changes and net ecosystem productivity of a subalpine Norway spruce forest in the Swiss Alps. New Phytologist 187, 819-830. doi: 10.1111/j.1469-8137.2010.03301.x

Zweifel, R., Haeni, M., Buchmann, N., and Eugster, W. (2016). Are trees able to grow in periods of stem shrinkage? New Phytologist 211, 839-849. DOI: 10.1111/nph.13995

Zweifel, R., and Sterck, F. (2018). A conceptual tree model explaining legacy effects on stem growth. Frontiers in Plant Sciences, in review.

How to Cite
Burri, S., Haeler, E., Eugster, W., Haeni, M., Etzold, S., Walthert, L., Braun, S., & Zweifel, R. (2019). How did Swiss forest trees respond to the hot summer 2015?. DIE ERDE – Journal of the Geographical Society of Berlin, 150(4), 214-229. Retrieved from
Research articles