How has climate change affected EU forests and what might happen next?
Climate change is ongoing and recent global temperatures are already more than one degree above the pre-industrial levels, with some regional differences (stronger warming especially in higher latitudes). Besides the warming trend, extreme events have been amplified with extended periods of hot spells and drought. For example, the years 2018 to 2020 were exceptionally warm and in large parts of Europe also particularly dry. Consequently, in recent years, European forests have been affected by severe droughts, widespread wildfires, a series of windstorms, rapidly expanding bark beetle infestations and several other pest and disease outbreaks. Evidence is increasing that these events have become much more frequent and more threatening because of climate change (Seidl et al., 2014; Seidl et al., 2017).
These changes constitute a major challenge for future forest management. Climate change and associated extreme events are already affecting the growth and stability of forests in Europe. While the analysis of forest growth changes in the late 20th century showed nitrogen deposition as a major explanatory factor with only limited contribution of CO2 fertilization and climate change (Kahle et al., 2008), empirical growth trend analysis extending to 2010 showed that climate warming and extended growing season explained a substantial part of the growth enhancement observed around the year 2000 (Pretzsch et al., 2014). Increased forest productivity due to climate warming was observed in high latitudes (Henttonen et al., 2017) and in higher altitudes of mountainous regions (Sedmáková et al., 2019). Dendrochronological studies indicate that tree growth responses at low elevations differed from higher elevations and growth of spruce and beech declined 1991–2012 compared to 1961-1990 in the sub-montane belt (Sedmáková et al., 2019). Where temperature increases occurred in combination with extended periods of below average amounts of precipitation, trees may suffer from drought stress. Drought induced growth declines have increasingly been observed at the dry distribution limits of species such as in the Wallis in Switzerland (Bigler et al., 2006), but also in temperate lowland forests in Belgium (Kint et al., 2012). The recent exceptionally long and intensive drought in Central Europe from 2018 onwards drastically exceeded previous impacts and resulted in widespread mortality in different species (Buras et al., 2020; Schuldt et al., 2020). A major consequence of the intensive drought was the widespread bark beetle outbreak affecting Norway spruce forests in Central Europe (Jakoby et al., 2019; Netherer et al., 2019), causing exceptionally large amounts of sanitary fellings and salvage cutting on more than a million hectares of spruce forests with subsequently saturated wood markets and collapsing saw log prices on wood markets for example in the Czech Republic, Austria and Germany. In Mediterranean forests in southern Europe intensified drought impacts affected tree mortality, resulting in shifting species distribution limits (e.g. Dorado-Liñán et al., 2019; Peñuelas and Boada, 2003; Vayreda et al., 2016).
Another direct impact of climate change on European forests has been increased wildfire damages (Fernandes, 2019; Moreira et al., 2020; San-Miguel-Ayanz et al., 2013). Due to increased temperatures and extended drought periods, more forest area across Europe is exposed to high fire risk, for longer periods of time. In recent years devastating megafires occurred with high numbers of fatalities e.g. in Portugal (2017) and Greece (2018), but also countries like Sweden, UK, Germany or Poland had excessive burned areas at levels not experienced in the recent past.
The future evolution of climate change impacts can hardly be predicted due to a number of fundamental uncertainties about the future development of anthropogenic climate forcing and the resulting earth system dynamics:
- The uncertain level of climate warming during the 21st century. It is obvious that European forests will continue to be impacted by continuously changing climate conditions and extreme events. These impacts will directly relate to the success of global climate protection policies. If the world succeeds in curbing and eventually reversing the growth of greenhouse gas concentrations in the atmosphere according to the Paris agreements under UNFCCC, the scale of impacts will stay more manageable. With every additional degree of climatic warming, the climate and biogeochemical systems will further reach into unchartered terrain. Recent climatic extremes have already demonstrated far reaching shifts in large scale global weather patterns (Kornhuber et al., 2020; Kornhuber et al., 2019), but there is no empirical basis available to simulate future changes in these global scale processes, as melting Arctic and Antarctic ice shields and a slowing gulf stream may act as tipping points in the earth system with unknown consequences (Lenton et al., 2019).
- The future evolution of extreme events in the changing climate. The intensity of forest damage in recent years has increased more than expected as climate change induced extreme events were more severe than previously projected (Lorenz et al., 2019). It is unknown, how unusual or rare the recent extreme weather patterns of 2018-2020 will turn out to be when we look back from the year 2030 or 2050. In a positive scenario, Europe may experience more average climate conditions in the coming years and the length of the drought from 2018 to 2020 in Central Europe could stand out as exceptional for many years. However, it is equally possible or likely that exceptionally dry and wet periods will become the new normal, or even worse, that future extreme events will become even more extreme. European forests are thought to be resilient and are likely to recover from the present extreme events (Honkaniemi et al., 2020; Seidl et al., 2019) but with more frequent and more devastating extreme events, the resistance of present forest types may reach critical thresholds (McDowell et al., 2020).
- The effect of CO2 fertilization on forest productivity and water use efficiency. Projected impacts of climate change in European forests are quite sensitive to the impacts of increasing CO2 concentrations in the atmosphere (Reyer, 2015), but model validations against observations revealed large uncertainties in projections of current process-based vegetation models (Piao et al., 2013). Essentially it is still difficult to generalize from CO2 fertilization experiments to forest ecosystem responses under changing conditions, but it is highly likely that increases in terrestrial carbon storage as a result of increased CO2 will decline into the future (Walker et al., 2020).
- The future integrated effects of productivity changes and disturbance impacts. European forests have been a carbon sink for many decades (Luyssaert et al., 2010), but the future balance between productivity changes and disturbance impacts is uncertain (Nabuurs et al., 2013; Reyer et al., 2017). Forest management has the potential to mitigate some of the expected enhanced disturbance impacts (Fernandes, 2013; Hlásny et al., 2019), but this will require concerted efforts at many different levels (Castellnou et al., 2019; Verkerk et al., 2018).
- The adaptive capacity of trees and forest ecosystems. Forest trees have considerable adaptive capacity (Aitken et al., 2008), but the extent of environmental changes expected is exceeding historical precedents. The present rate and magnitude of climate change exceeds the natural migration and adaptation capacity of tree species. Future species suitability is difficult to predict as we do not know well how trees can adapt to adverse conditions. Existing models still need improvement to make them really useful in guiding forest management (Dyderski et al., 2018; Pecchi et al., 2019). Assisted migration will be needed to a considerable extent to support sustainable forest management (Fady et al., 2016).
Aitken, S.N., Yeaman, S., Holliday, J.A., Wang, T., Curtis‐McLane, S. (2008) Adaptation, migration or extirpation: climate change outcomes for tree populations. Evolutionary Applications 1, 95-111.
Bigler, C., Bräker, O., Bugmann, H., Dobbertin, M., Rigling, A. (2006) Drought as an Inciting Mortality Factor in Scots Pine Stands of the Valais, Switzerland. Ecosystems 9, 330-343.
Buras, A., Rammig, A., Zang, C.S. (2020) Quantifying impacts of the 2018 drought on European ecosystems in comparison to 2003. Biogeosciences 17, 1655-1672.
Castellnou, M., Prat-Guitart, N., Arilla, E., Larrañaga, A., Nebot, E., Castellarnau, X., Vendrell, J., Pallàs, J., Herrera, J., Monturiol, M., Cespedes, J., Pagès, J., Gallardo, C., Miralles, M. (2019) Empowering strategic decision-making for wildfire management: avoiding the fear trap and creating a resilient landscape. Fire Ecology 15, 31.
Dorado-Liñán, I., Piovesan, G., Martínez-Sancho, E., Gea-Izquierdo, G., Zang, C., Cañellas, I., Castagneri, D., Di Filippo, A., Gutiérrez, E., Ewald, J., Fernández-de-Uña, L., Hornstein, D., Jantsch, M.C., Levanič, T., Mellert, K.H., Vacchiano, G., Zlatanov, T., Menzel, A. (2019) Geographical adaptation prevails over species-specific determinism in trees’ vulnerability to climate change at Mediterranean rear-edge forests. Global Change Biology 25, 1296-1314.
Dyderski, M.K., Paź, S., Frelich, L.E., Jagodziński, A.M. (2018) How much does climate change threaten European forest tree species distributions? Global Change Biology 24, 1150-1163.
Fady, B., Cottrell, J., Ackzell, L., Alía, R., Muys, B., Prada, A., González-Martínez, S. (2016) Forests and global change: what can genetics contribute to the major forest management and policy challenges of the twenty-first century? Regional Environmental Change 16, 927–939.
Fernandes, P.M. (2013) Fire-smart management of forest landscapes in the Mediterranean basin under global change. Landscape and Urban Planning 110, 175-182.
Fernandes, P.M. (2019) Variation in the Canadian Fire Weather Index Thresholds for Increasingly Larger Fires in Portugal. Forests 10, 838.
Henttonen, H.M., Nöjd, P., Mäkinen, H. (2017) Environment-induced growth changes in the Finnish forests during 1971–2010 – An analysis based on National Forest Inventory. Forest Ecology and Management 386, 22-36.
Hlásny, T., Krokene, P., Liebhold, A., Montagné-Huck, C., Müller, J., Qin, H., Raffa, K., Schelhaas, M.-J., Seidl, R., Svoboda, M., Viiri, H., (2019) Living with bark beetles: impacts, outlook and management options, From Science to Policy 8. European Forest Institute. https://doi.org/10.36333/fs08
Honkaniemi, J., Rammer, W., Seidl, R. (2020) Norway spruce at the trailing edge: the effect of landscape configuration and composition on climate resilience. Landscape Ecology 35, 591-606.
Jakoby, O., Lischke, H., Wermelinger, B. (2019) Climate change alters elevational phenology patterns of the European spruce bark beetle (Ips typographus). Global Change Biology 25, 4048-4063.
Kahle, H.P., Karjalainen, T., Schuck, A., Ågren, G.I., Kellomäki, S., Mellert, K.H., Prietzel, J., Rehfuess, K.E., Spiecker, H., (2008) Causes and Consequences of Forest Growth Trends in Europe - Results of the RECOGNITION Project, EFI Research Report. Brill Leiden, Boston, Köln.
Kint, V., Aertsen, W., Campioli, M., Vansteenkiste, D., Delcloo, A., Muys, B. (2012) Radial growth change of temperate tree species in response to altered regional climate and air quality in the period 1901-2008. Climatic Change 115, 343-363.
Kornhuber, K., Coumou, D., Vogel, E., Lesk, C., Donges, J.F., Lehmann, J., Horton, R.M. (2020) Amplified Rossby waves enhance risk of concurrent heatwaves in major breadbasket regions. Nature Climate Change 10, 48-53.
Kornhuber, K., Osprey, S., Coumou, D., Petri, S., Petoukhov, V., Rahmstorf, S., Gray, L. (2019) Extreme weather events in early summer 2018 connected by a recurrent hemispheric wave-7 pattern. Environmental Research Letters 14, 054002.
Lenton, T.M., Rockström, J., Gaffney, O., Rahmstorf, S., Richardson, K., Steffen, W., Schellnhuber, H.J. (2019) Climate tipping points - too risky to bet against. Nature 575, 592-595.
Lorenz, R., Stalhandske, Z., Fischer, E.M. (2019) Detection of a Climate Change Signal in Extreme Heat, Heat Stress, and Cold in Europe From Observations. Geophysical Research Letters 46, 8363-8374.
Luyssaert, S., Ciais, P., Piao, S.L., Schulze, E.-D., Jung, M., Zaehle, S., Schelhaas, M.J., Reichstein, M., Churkina, G., Papale, D., Abril, G., Beer, C., Grace, J., Loustau, D., Matteucci, G., Magnani, F., Nabuurs, G.J., Verbeeck, H., Sulkava, M., WERF, G.R.v.d., Janssens, I.A. (2010) The European carbon balance: part 3: Forests. Global Change Biology 16, 1429-1450.
McDowell, N.G., Allen, C.D., Anderson-Teixeira, K., Aukema, B.H., Bond-Lamberty, B., Chini, L., Clark, J.S., Dietze, M., Grossiord, C., Hanbury-Brown, A., Hurtt, G.C., Jackson, R.B., Johnson, D.J., Kueppers, L., Lichstein, J.W., Ogle, K., Poulter, B., Pugh, T.A.M., Seidl, R., Turner, M.G., Uriarte, M., Walker, A.P., Xu, C. (2020) Pervasive shifts in forest dynamics in a changing world. Science 368, eaaz9463.
Moreira, F., Ascoli, D., Safford, H., Adams, M.A., Moreno, J.M., Pereira, J.M.C., Catry, F.X., Armesto, J., Bond, W., González, M.E., Curt, T., Koutsias, N., McCaw, L., Price, O., Pausas, J.G., Rigolot, E., Stephens, S., Tavsanoglu, C., Vallejo, V.R., Van Wilgen, B.W., Xanthopoulos, G., Fernandes, P.M. (2020) Wildfire management in Mediterranean-type regions: paradigm change needed. Environmental Research Letters 15, 011001.
Nabuurs, G.-J., Lindner, M., Verkerk, P.J., Gunia, K., Deda, P., Michalak, R., Grassi, G. (2013) First signs of carbon sink saturation in European forest biomass. Nature Climate Change 3, 792–796.
Netherer, S., Panassiti, B., Pennerstorfer, J., Matthews, B. (2019) Acute Drought Is an Important Driver of Bark Beetle Infestation in Austrian Norway Spruce Stands. Frontiers in Forests and Global Change 2.
Pecchi, M., Marchi, M., Burton, V., Giannetti, F., Moriondo, M., Bernetti, I., Bindi, M., Chirici, G. (2019) Species distribution modelling to support forest management. A literature review. Ecological Modelling 411, 108817.
Peñuelas, J., Boada, M. (2003) A global change-induced biome shift in the Montseny mountains (NE Spain). Global Change Biology 9, 131-140.
Piao, S., Sitch, S., Ciais, P., Friedlingstein, P., Peylin, P., Wang, X., Ahlström, A., Anav, A., Canadell, J.G., Cong, N., Huntingford, C., Jung, M., Levis, S., Levy, P.E., Li, J., Lin, X., Lomas, M.R., Lu, M., Luo, Y., Ma, Y., Myneni, R.B., Poulter, B., Sun, Z., Wang, T., Viovy, N., Zaehle, S., Zeng, N. (2013) Evaluation of terrestrial carbon cycle models for their response to climate variability and to CO2 trends. Global Change Biology 19, 2117-2132.
Pretzsch, H., Biber, P., Schütze, G., Uhl, E., Rötzer, T. (2014) Forest stand growth dynamics in Central Europe have accelerated since 1870. Nat Commun 5, 4967.
Reyer, C. (2015) Forest Productivity Under Environmental Change—a Review of Stand-Scale Modeling Studies. Current Forestry Reports 1, 1-16.
Reyer, C.P.O., Bathgate, S., Blennow, K., Borges, J.G., Bugmann, H., Delzon, S., Faias, S.P., Garcia-Gonzalo, J., Gardiner, B., Gonzalez-Olabarria, J.R., Gracia, C., Hernández, J.G., Kellomäki, S., Kramer, K., Lexer, M.J., Lindner, M., van der Maaten, E., Maroschek, M., Muys, B., Nicoll, B., Palahi, M., Palma, J.H.N., Paulo, J.A., Peltola, H., Pukkala, T., Rammer, W., Ray, D., Sabaté, S., Schelhaas, M.-J., Seidl, R., Temperli, C., Tomé, M., Yousefpour, R., Zimmermann, N.E., Hanewinkel, M. (2017) Are forest disturbances amplifying or canceling out climate change-induced productivity changes in European forests? Environmental Research Letters 12, 034027.
San-Miguel-Ayanz, J., Moreno, J.M., Camia, A. (2013) Analysis of large fires in European Mediterranean landscapes: Lessons learned and perspectives. Forest Ecology and Management 294, 11-22.
Schuldt, B., Buras, A., Arend, M., Vitasse, Y., Beierkuhnlein, C., Damm, A., Gharun, M., Grams, T.E.E., Hauck, M., Hajek, P., Hartmann, H., Hilbrunner, E., Hoch, G., Holloway-Phillips, M., Körner, C., Larysch, E., Lübbe, T., Nelson, D.B., Rammig, A., Rigling, A., Rose, L., Ruehr, N.K., Schumann, K., Weiser, F., Werner, C., Wohlgemuth, T., Zang, C.S., Kahmen, A. (2020) A first assessment of the impact of the extreme 2018 summer drought on Central European forests. Basic and Applied Ecology.
Sedmáková, D., Sedmák, R., Bosela, M., Ježík, M., Blaženec, M., Hlásny, T., Marušák, R. (2019) Growth-climate responses indicate shifts in the competitive ability of European beech and Norway spruce under recent climate warming in East-Central Europe. Dendrochronologia 54, 37-48.
Seidl, R., Albrich, K., Erb, K., Formayer, H., Leidinger, D., Leitinger, G., Tappeiner, U., Tasser, E., Rammer, W. (2019) What drives the future supply of regulating ecosystem services in a mountain forest landscape? Forest Ecology and Management 445, 37-47.
Seidl, R., Schelhaas, M.-J., Rammer, W., Verkerk, P.J. (2014) Increasing forest disturbances in Europe and their impact on carbon storage. Nature Clim. Change 4, 806-810.
Seidl, R., Thom, D., Kautz, M., Martin-Benito, D., Peltoniemi, M., Vacchiano, G., Wild, J., Ascoli, D., Petr, M., Honkaniemi, J., Lexer, M.J., Trotsiuk, V., Mairota, P., Svoboda, M., Fabrika, M., Nagel, T.A., Reyer, C.P.O. (2017) Forest disturbances under climate change. Nature Climate Change 7, 395-402.
Vayreda, J., Martinez-Vilalta, J., Gracia, M., Canadell, J.G., Retana, J. (2016) Anthropogenic-driven rapid shifts in tree distribution lead to increased dominance of broadleaf species. Global Change Biology 22, 3984-3995.
Verkerk, P.J., Martinez de Arano, I., Palahí, M. (2018) The bio-economy as an opportunity to tackle wildfires in Mediterranean forest ecosystems. Forest Policy and Economics 86, 1-3.
Walker, A.P., De Kauwe, M.G., Bastos, A., Belmecheri, S., Georgiou, K., Keeling, R.F., McMahon, S.M., Medlyn, B.E., Moore, D.J.P., Norby, R.J., Zaehle, S., Anderson-Teixeira, K.J., Battipaglia, G., Brienen, R.J.W., Cabugao, K.G., Cailleret, M., Campbell, E., Canadell, J.G., Ciais, P., Craig, M.E., Ellsworth, D.S., Farquhar, G.D., Fatichi, S., Fisher, J.B., Frank, D.C., Graven, H., Gu, L., Haverd, V., Heilman, K., Heimann, M., Hungate, B.A., Iversen, C.M., Joos, F., Jiang, M., Keenan, T.F., Knauer, J., Körner, C., Leshyk, V.O., Leuzinger, S., Liu, Y., MacBean, N., Malhi, Y., McVicar, T.R., Penuelas, J., Pongratz, J., Powell, A.S., Riutta, T., Sabot, M.E.B., Schleucher, J., Sitch, S., Smith, W.K., Sulman, B., Taylor, B., Terrer, C., Torn, M.S., Treseder, K.K., Trugman, A.T., Trumbore, S.E., van Mantgem, P.J., Voelker, S.L., Whelan, M.E., Zuidema, P.A. (2020) Integrating the evidence for a terrestrial carbon sink caused by increasing atmospheric CO2. New Phytologist doi 10.1111/nph.16866.