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Global change affects the functioning of forest ecosystems and the services they provide, but little is known about the interactive effects of co-occurring global change drivers on important functions such as tree growth and vitality. In the present study we quantified the interactive (i.e. synergistic or antagonistic) effects of atmospheric nitrogen (N) deposition and climatic variables (temperature, precipitation) on tree growth (in terms of tree-ring width, TRW), taking forest ecosystems with European beech (Fagus sylvatica L.) as an example. We hypothesised that (i) N deposition and climatic variables can evoke non-additive responses of the radial increment of beech trees, and (ii) N loads have the potential to strengthen the trees' sensitivity to climate change. In young stands, we found a synergistic positive effect of N deposition and annual mean temperature on TRW, possibly linked to the alleviation of an N shortage in young stands. In mature stands, however, high N deposition significantly increased the trees’ sensitivity to increasing annual mean temperatures (antagonistic effect on TRW), possibly due to increased fine root dieback, decreasing mycorrhizal colonization or shifts in biomass allocation patterns (aboveground vs. belowground). Accordingly, N deposition and climatic variables caused both synergistic and antagonistic effects on the radial increment of beech trees, depending on tree age and stand characteristics. Hence, the nature of interactions could mediate the long-term effects of global change drivers (including N deposition) on forest carbon sequestration. In conclusion, our findings illustrate that interaction processes between climatic variables and N deposition are complex and have the potential to impair growth and performance of European beech. This in turn emphasises the importance of multiple-factor studies to foster an integrated understanding and models aiming at improved projections of tree growth responses to co-occurring drivers of global change. Global change affects the functioning of forest ecosystems and the services they provide, but little is known about the interactive effects of co-occurring global change drivers on important functions such as tree growth and vitality. In the present study we quantified the interactive (i.e. synergistic or antagonistic) effects of atmospheric nitrogen (N) deposition and climatic variables (temperature, precipitation) on tree growth (in terms of tree-ring width, TRW), taking forest ecosystems with European beech (Fagus sylvatica L.) as an example. We hypothesised that (i) N deposition and climatic variables can evoke non-additive responses of the radial increment of beech trees, and (ii) N loads have the potential to strengthen the trees' sensitivity to climate change. In young stands, we found a synergistic positive effect of N deposition and annual mean temperature on TRW, possibly linked to the alleviation of an N shortage in young stands. In mature stands, however, high N deposition significantly increased the trees’ sensitivity to increasing annual mean temperatures (antagonistic effect on TRW), possibly due to increased fine root dieback, decreasing mycorrhizal colonization or shifts in biomass allocation patterns (aboveground vs. belowground). Accordingly, N deposition and climatic variables caused both synergistic and antagonistic effects on the radial increment of beech trees, depending on tree age and stand characteristics. Hence, the nature of interactions could mediate the long-term effects of global change drivers (including N deposition) on forest carbon sequestration. In conclusion, our findings illustrate that interaction processes between climatic variables and N deposition are complex and have the potential to impair growth and performance of European beech. This in turn emphasises the importance of multiple-factor studies to foster an integrated understanding and models aiming at improved projections of tree growth responses to co-occurring drivers of global change.

Das Fachwissen zum Klima in der Metropolregion Hamburg (MRH) und seinen Anderungen wurde bis 2008 ausfuhrlich im „Klimabericht fur die Metropolregion Hamburg“ dokumentiert (Rosenhagen und Schatzmann 2011; Daschkeit 2011). Im Jahr 2013 haben die Leitautoren im Rahmen einer Aktualisierung des Klimaberichtes bzgl. dieses Themenfeldes auf das BMBF‐Projekt KLIMZUG‐NORD und das Hamburger Exzellenzcluster CliSAP sowie erste daraus entstandene Arbeiten verwiesen (Rosenhagen 2013), die sich vielfach auf das Stadtklima Hamburgs beziehen (vgl. Kap. 3). Inzwischen stehen fur weitere Regionen in Norddeutschland Ergebnisse aus verschiedenen Forschungsprojekten wie KLIWAS (Bulow et al. 2014), KLIFF (Moseley et al. 2012), KLIMZUG‐NORD (Rechid et al. 2014b, 2014c) und RADOST (Martinez und Blobel 2015) zur Verfugung. Zudem sind seit 2013 weitere Fachartikel erschienen, die das Klima und den Klimawandel in der Region thematisieren. Bezuglich der Veroffentlichungen ist insbesondere der 2015 veroffentlichte Klimabericht fur den Ostseeraum (BACC II Author Team 2015) zu nennen, der ahnlich wie der Hamburger Klimabericht (HKB) den Stand des Wissens zum regionalen Klima sowie dessen zeitliche Veranderungen und Folgen fur den Ostseeraum dokumentiert. Zudem wurden neben neuen Fachartikeln webbasierte Informationsangebote entwickelt, die das Klima und den Klimawandel in der Region thematisieren (Tab. 2.1).

The term “climate services” is commonly used to refer to the generation of climate information, their transformation according to user needs and the subsequent use of the information in decision making processes. More generally, the concept also involves contextualization of information and knowledge. In the following a series of examples from the marine sector is described covering the generation, transformation and the use of climate information in decision making processes while contextualization is not considered. Examples comprise applications from naval architecture, offshore wind and more generally renewable energies, shipping emissions, and tidal basin water exchange and eutrophication levels. Moreover effects of climate change on coastal flood damages and the need for coastal protection are considered. Based on the analysis of these examples it is concluded that reliable climate information in data sparse regions is urgently needed, that for many applications historical climate information may be as or even more important as future long-term projections, and that the specific needs of different sectors substantially depend on their planning horizons.