Department of Forest and Soil Sciences Institute of Silviculture Supervisor: Assoc.Prof. DI Dr. Rupert Seidl DISTURBANCE IMPACTS ON FOREST SUCCESSION, BIODIVERSITY, AND ECOSYSTEM SERVICES IN A CHANGING WORLD Dissertation to obtain a doctoral degree (Dr.nat.techn.) at the University of Natural Resources and Life Sciences, Vienna Dominik Thom Vienna, August 2016 “A society grows great when old men plant trees whose shade they know they shall never sit in.” Greek Proverb I Preface The main body of this thesis comprises three peer-reviewed scientific papers which can be found in the Appendix of this work (sections 9.1 to 9.3). Please note that the format of each article follows the requirements of the respective journal. Whereas detailed descriptions of the experimental design and results of my work can be found in each paper, the synthesis of sections 1-8 aims to frame and interlink the findings of my dissertation in order to highlight the contribution of my thesis to filling existing knowledge gaps on disturbance dynamics in a changing world. In this way, my synthesis provides a common structure for the individual articles, and stimulates a discussion of the results beyond the scope of each paper. Moreover, I here present new hypotheses based on the advances made in my thesis, which I consider worth investigating in the future. I hope the reader of my thesis feels excited by the research provided here and gains inspiration for his or her own investigations. I also like to mention that although I am certain about the validity of the methods used in this study, as in all fields of natural sciences no results should be considered without uncertainty. If there is one thing I learned during my PhD, it is that nothing we do and conclude from our findings is just black and white, but everything is shaded in grey. Hence, I believe that there is no perfect solution to a problem or only one outcome, but one can strive to find a good compromise and reduce the uncertainty among possible outcomes. Please cite this thesis either by referring to the respective article: Thom, D., Rammer, W., Dirnböck, T., Müller, J., Kobler, J., Katzensteiner, K., Helm, N., Seidl, R., 2016. The impacts of climate change and disturbance on spatio-temporal trajectories of biodiversity in a temperate forest landscape. J. Appl. Ecol., DOI: 10.1111/1365-2664.12644 Thom, D., Rammer, W., Seidl, R., 2016. Disturbances catalyze the adaptation of forest ecosystems to changing climate conditions. Glob. Chang. Biol. (accepted with minor revision) Thom, D., Seidl, R., 2016. Natural disturbance impacts on ecosystem services and biodiversity in temperate and boreal forests. Biol. Rev. 91, 760–781. II or by quoting it in its entirety as: Thom, D. (2016) Disturbance impacts on forest succession, biodiversity and ecosystem services provisioning in a changing world. Dissertation, University of Natural Resources and Life Sciences (BOKU), Vienna, p.188 III Abstract Forest ecosystems are dominated by long-living organisms with limited ability to migrate in space and time. Rapid changes in the climate system cause an increasing maladaptation of forests to their environment. Besides the direct impacts of climate change on forest ecosystems, climate change also modifies natural disturbance regimes. During the last decades, disturbance activity has significantly increased in many parts of the world, and a further increase as a result of climate change is very likely. Yet there is high uncertainty about the impacts of climate change and disturbance on the conservation of biodiversity and the provisioning of ecosystem services to society. This thesis aimed to reduce this uncertainty by (i) synthesizing the effects of natural disturbances on biodiversity and ecosystem services in a global literature review, (ii) assessing the long-term development of tree species under varying climate and disturbance regimes by means of process-based landscape modelling, and (iii) investigating the role of climate change and disturbances on a wide range of forest biodiversity indicators in space and time. I screened in total 1958 peer-reviewed papers for disturbance impact on biodiversity and ecosystem services, and reviewed 478 in detail. Subsequently, I simulated the autonomous adaptation of forests and their associated biodiversity under different climate and disturbance scenarios at Kalkalpen National Park (KANP). To account for the complexity of changes in ecosystems I employed the individual-based forest landscape and disturbance model (iLand). I found strongly diverging disturbance impacts on forests: while disturbances increased biodiversity, they decreased ecosystem services provisioning. My results indicated that tree vegetation and associated biodiversity take centuries to adapt to changed climatic conditions, but also revealed a catalyzing effect of disturbances accelerating adaptation to a changing environment. I conclude that disturbances create opportunities for ecosystems to reorganize themselves with potentially positive implications for the biodiversity and resilience of future forest ecosystems. Management should focus on the diversification of forests to provide ecosystems with the flexibility to react on changes of the environment and safeguard biodiversity and ecosystem services provisioning in a changing world. IV Keywords: autonomous adaptation, biodiversity, climate change, disturbance, ecosystem services, forest ecosystem management, forest ecosystem dynamics, iLand, modelling, succession V Kurzfassung Waldökosysteme werden von langlebigen Organismen dominiert, die nur bedingt ihren Standort verändern können. Der schnell voranschreitende Klimawandel kann somit zu einer Fehlanpassung von Ökosystemen an ihre Umweltbedingungen führen. Das Klima verändert Ökosysteme jedoch nicht nur direkt, sondern auch über Änderungen im Störungsregime. In den letzten Jahrzehnten wurde bereits ein Anstieg von Störungen in vielen Teilen der Welt beobachtet und eine weitere Zunahme gilt als sehr wahrscheinlich. Bislang herrscht große Unsicherheit über die Wirkung von Klimawandel und Störungen auf Biodiversität und Ökosystemleistungen. Mit meiner Dissertation habe ich daher (i) die Effekte natürlicher Störungen auf Biodiversität und Ökosystemleistungen mithilfe einer globalen Übersichtsarbeit untersucht, (ii) die langfristige Entwicklung der Baumartenvegetation unter Annahme verschiedener Klima- und Störungsszenarien mit einem prozessbasierten Landschaftsmodel simuliert und (iii) die Rolle von Klimawandel und Störungen auf eine Reihe von unterschiedlichen Biodiversitätsindikatoren räumlich und zeitlich abgeschätzt. Insgesamt habe ich 1958 wissenschaftliche Artikel auf ihren Inhalt überprüft und 478 für die Analyse von Störungseffekten auf Biodiversität und Ökosystemleistungen einbezogen. Anschließend habe ich die autonome Anpassung von Wäldern und ihrer Biodiversität im Nationalpark Kalkalpen unter verschiedenen Klima- und Störungsszenarien simuliert. Um der Komplexität von Ökosystemen gerecht zu werden, habe ich das individuenbasierte Waldlandschafts- und Störungsmodell (iLand) benutzt. In meiner Studie konnte ich stark unterschiedliche Störungseffekte identifizieren und zeigen, dass Störungen Biodiversität erhöhen, aber gleichzeitig Ökosystemleistungen reduzieren. Simulationen zeigten einen Anpassungszeitraum der Baumvegetation und assoziierter Biodiversität auf veränderte Klimabedingungen von mehreren Jahrhunderten, aber auch eine Beschleunigung des Anpassungsprozesses durch Störungen. Meine Schlussfolgerung ist, dass Störungen eine Chance für die Reorganisation von Ökosystemen bedeuten und positive Folgen für die Biodiversität und Resilienz von zukünftigen Waldökosystemen haben können. Managementstrategien sollten sich auf die Förderung von Biodiversität konzentrieren, damit Waldökosysteme den drastischen VI Umweltänderungen gewappnet sind und auch in Zukunft Biodiversität erhalten sowie Ökosystemleistungen bereitstellen können. Stichwörter: autonome Anpassung, Biodiversität, iLand, Klimawandel, Modellierung, Ökosystemleistungen, Störungen, Sukzession, Waldökosystemdynamik, Waldökosystemmanagement VII Contents 1 Introduction ......................................................................................................................... 1 2 Objectives ........................................................................................................................... 4 3 Materials and Methods ........................................................................................................ 5 3.1 Workflow ..................................................................................................................... 5 3.2 Literature review and meta-analysis ............................................................................ 6 3.3 Case study area ............................................................................................................ 7 3.4 Simulation model ......................................................................................................... 7 3.5 Initial conditions and drivers ....................................................................................... 8 3.6 Simulation design ........................................................................................................ 9 3.7 Analysis of autonomous adaptation of tree vegetation .............................................. 10 3.8 Analysis of trajectories of biodiversity ...................................................................... 10 4 Results