Student thesis series INES nr 350 Occurrences of insect outbreaks in Sweden in relation to climatic parameters since 1850 Mihaela – Mariana Tudoran 2015 Department of Physical Geography and Ecosystem Science Lund University Sölvegatan 12 S -223 62 Lund Sweden Mihaela-Mariana Tudoran (2015). Occurrences of insect outbreaks in Sweden in relation to climatic parameters since 1850. Master degree thesis, 30 credits in Physical Geography and Ecosystem Analysis. Department of Physical Geography and Ecosystem Science, Lund University Level: Master of Science (MSc) Course duration: January 2015 until June 2015 Disclaimer This document describes work undertaken as part of a program of study at the University of Lund. All views and opinions expressed herein remain the sole responsibility of the author, and do not necessarily represent those of the institute. Occurrences of insect outbreaks in Sweden in relation to climatic parameters since 1850 Mihaela – Mariana Tudoran Master thesis, 30 credits, in Physical Geography and Ecosystem Analysis Supervisors: Anna Maria Jönsson and Laurent Marquer, Department of Physical Geography and Ecosystem Science Lund University, Sweden Examiners: Anneli Poska and Dan Metcalfe, Department of Physical Geography and Ecosystem Science Lund University, Sweden Course coordinator: Harry Lankreijer Department of Physical Geography and Ecosystem Science Lund University 2015 Acknowledgment I would like to express my sincere thanks to my supervisors, Anna Maria Jönsson and Laurent Marquer. I am grateful for their constant support, inspiration and patience during the entire working process and also for helping me all along, enabled me to implement the analyses and get some interesting results. I am also grateful to Harry Lankreijer for accepting me in this program. I would like to mention that this project was done using a mobility scholarship through Erasmus+ program and by providing a learning agreement between Lund University, Sweden and University of Agronomic Science and Veterinary Medicine, Bucharest and with this occasion I would like to thank Paul Miller and Ecaterina Stefan for their time invested in achieving agreement between the two Universities. i Table of contents Abstract ....................................................................................................................................................... iv 1. Introduction ............................................................................................................................................. 1 2. Background ............................................................................................................................................. 3 2.1. Study area........................................................................................................................................... 3 2.2. Why Sweden is important to explore insect outbreaks ...................................................................... 4 2.3. Vegetation and climate in Sweden ..................................................................................................... 5 2.3.1 Present day vegetation and climate .............................................................................................. 5 2.3.2 Past vegetation and climate .......................................................................................................... 6 2.4 Insect outbreaks .................................................................................................................................. 7 2.4.1 Definition ..................................................................................................................................... 7 2.4.2 Types of insect outbreaks ............................................................................................................. 8 2.4.3 Causes and consequences of insect outbreaks ............................................................................. 9 2.4.4 What do we know regarding past and present insect outbreaks ................................................. 11 3. Materials and Methods ......................................................................................................................... 16 3.1. Datasets ............................................................................................................................................ 16 3.2. Extraction of data ............................................................................................................................. 18 3.3. Evaluate the major trends of insect outbreaks.................................................................................. 19 3.4. Creating temporal maps ................................................................................................................... 21 3.5. Analyzing the influence of climate on the occurrences of insect outbreaks through time ............... 22 4. Results .................................................................................................................................................... 25 4.1. Insect host trees per year: attacked broadleaved trees versus attacked coniferous trees .................. 25 4.2. Occurrences of insect outbreaks ...................................................................................................... 26 4.3. Top five families responsible for outbreak occurrences .................................................................. 31 4.3.1. Southern Sweden....................................................................................................................... 31 4.3.2. Central Sweden ......................................................................................................................... 32 4.3.3. Northern Sweden....................................................................................................................... 34 4.4. Top species responsible for outbreak occurrences ........................................................................... 35 4.4.1. Southern Sweden....................................................................................................................... 35 4.4.2. Central Sweden ......................................................................................................................... 37 4.4.3. Northern Sweden....................................................................................................................... 39 4.5. Climate influence on the occurrences of insect outbreaks ............................................................... 40 ii 4.5.1. Southern Sweden....................................................................................................................... 42 4.5.2. Central Sweden ......................................................................................................................... 43 4.5.3. Northern Sweden....................................................................................................................... 45 5. Discussion............................................................................................................................................... 47 5.1. Occurrences of insects responsible for outbreaks during 1850-1950 under climate influence ........ 47 5.1.1. Southern Sweden....................................................................................................................... 47 5.1.2. Central Sweden ......................................................................................................................... 50 5.1.3. Northern Sweden....................................................................................................................... 52 5.2. Occurrences of insects responsible for outbreaks during 1961 – 2014 ............................................ 54 5.2.1. Top insect species and climate variables .................................................................................. 54 5.2.2. Uncertainties due to the primary data ....................................................................................... 55 5.2.3. Forest management influence ................................................................................................... 56 5.3. Future implication ............................................................................................................................ 58 6. Conclusions ............................................................................................................................................ 60 References .................................................................................................................................................. 61 Appendices ................................................................................................................................................. 69 Top five families of insect species responsible for outbreaks ................................................................. 69 Top insect species responsible for outbreaks .......................................................................................... 70 Analysis of the occurrences of insect outbreaks in relation to climate parameters ................................. 72 Summary tables of the RDA analysis: .................................................................................................... 75 iii Abstract This study was carried out in order to identify the main insect species responsible for forest