The vegetation of Greek fir (Abies cephalonica Loudon) forests on the Oxia - North Vardousia mountain system, central Greece, in relation to drought Thesis submitted in partial fulfilment of the requirements of the degree Doctor rer. nat. of the Faculty of Forest and Environmental Sciences, Albert-Ludwigs-Universität Freiburg im Breisgau, Germany by Dimitrios A. Samaras Freiburg im Breisgau, Germany 2012 Dean of Faculty: Prof. Dr. Jürgen Bauhus First Supervisor: Prof. Dr. Dr. h.c. Albert Reif Second Supervisor: Assoc. Prof. Dr. Konstantinos Theodoropoulos Second Reviewer: Prof. Dr. Andreas Matzarakis Date of thesis’ defence: 11/06/2012 The vegetation of Greek fir (Abies cephalonica Loudon.) forests on the Oxia - North Vardousia mountain system, central Greece, in relation to drought This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this license please visit http://creativecommons.org/licenses/by/3.0/ 3 Contents Acknowledgments1 Abstract3 Zusammenfassung5 PerÐlhyh 9 1. Introduction 13 1.1. Morphological and genetic variation of the fir populations in Greece. 13 1.2. Biogeography and evolution of the fir populations in Greece..... 14 1.3. Ecology of Greek fir (Abies cephalonica Loudon)............ 15 1.4. Aim and objectives............................ 16 1.5. The Oxia - North Vardousia mountain system.............. 17 1.5.1. Physical geography........................ 17 1.5.2. Geology.............................. 18 1.5.3. Climate.............................. 18 1.5.4. Vegetation............................. 20 1.6. Study area................................. 21 2. Quantification of drought intensity 23 2.1. Overview.................................. 23 2.2. Definition of drought........................... 23 2.3. Analytical procedure for the quantification of drought intensity.... 25 2.3.1. Humidity index.......................... 25 2.3.2. Water balance........................... 26 2.3.2.1. Components of the water balance model....... 28 2.4. Evaluation of radiation-based PETref models.............. 30 2.4.1. Materials and methods...................... 31 2.4.1.1. Study area and climate................ 31 2.4.1.2. Generalization of radiation-based equations..... 35 2.4.1.3. Calibration and validation of the models....... 37 i Contents 2.4.1.4. Standardized calculations............... 38 2.4.2. Results............................... 40 2.4.2.1. Calibration of general models............. 40 2.4.2.2. Validation and comparison of performance...... 41 2.4.3. Discussion............................. 46 2.4.4. Conclusions............................ 50 2.5. Spatial prediction of climatic variables................. 51 2.5.1. Weather stations and climatic data............... 51 2.5.2. Ancillary data and software................... 52 2.5.2.1. Digital elevation data................. 52 2.5.2.2. Geospatial applications................. 53 2.5.2.3. Statistical tools..................... 53 2.5.3. Calculation of solar radiation.................. 54 2.5.4. Spatial prediction of air temperature and precipitation.... 57 2.5.4.1. Procedure........................ 59 2.6. Calculation of PETref ........................... 64 2.7. Soil hydraulic properties......................... 64 2.7.1. Water retention.......................... 64 2.7.2. Available soil water storage capacity.............. 65 2.8. Actual evapotranspiration function................... 66 2.9. Results................................... 70 2.9.1. Humidity index values...................... 70 2.9.2. Water balance outputs - AETref and water deficit....... 72 2.10. Discussion................................. 74 2.10.1. Modeling climatic variables on an uncertain base....... 74 2.10.2. Regression models vs. geostatistical methods for the spatial prediction of precipitation and temperature.......... 74 2.10.3. Solar radiation under overcast conditions............ 76 2.10.4. Water balance model - assumptions and limitations...... 76 2.10.5. The critical value of soil wetness for the calculation of actual evapotranspiration function................... 77 2.10.6. Strength and adequacy of the methods for the quantification of drought intensity........................ 78 3. Description and analysis of the Greek fir forest vegetation 79 3.1. Overview.................................. 79 3.2. Literature review............................. 79 3.2.1. Fir forest vegetation in Western & Central Sterea Ellas.... 79 ii Contents 3.2.1.1. Lilio chalcedonicae - Abietetum cephalonicae ..... 80 3.2.1.2. Abies cephalonica - community............ 81 3.2.1.3. Abies cephalonica - Lonicera graeca - community... 81 3.2.1.4. Helictotricho convoluti - Abietetum cephalonicae ... 82 3.2.1.5. Quercus ilex - Abies cephalonica - community.... 82 3.2.1.6. Trifolio grandiflori - Abietetum borisii-regis ...... 83 3.2.2. Syntaxonomic synopsis...................... 83 3.2.3. Synopsis of the phytosociological research on Greek fir forests 84 3.3. Materials and methods.......................... 87 3.3.1. Sampling design and stratification................ 87 3.3.2. Data collection.......................... 88 3.3.3. Preparation of the data...................... 89 3.3.3.1. Plant identification, nomenclature and ecology of the species.......................... 89 3.3.3.2. Syntaxonomy and nomenclature of syntaxa..... 89 3.3.3.3. Data exploration and adjustment........... 90 3.3.3.4. Software......................... 90 3.3.4. Climatic variables and soil hydraulic properties........ 91 3.3.5. Data analysis........................... 91 3.3.5.1. Classification of forest vegetation........... 91 3.3.5.2. Gradient analysis.................... 95 3.3.5.3. Classification trees analysis.............. 98 3.4. Results and partial discussion...................... 99 3.4.1. Vegetation units - syntaxonomy and synecology........ 101 3.4.1.1. Crepis fraasii - Abies cephalonica community.... 101 3.4.1.2. Sanicula europaea - Abies cephalonica community.. 110 3.4.2. Environmental thresholds.................... 116 3.5. General discussion............................ 118 3.5.1. Syntaxonomy of higher syntaxa................. 118 3.5.1.1. Crepis fraasii - Abies cephalonica community.... 118 3.5.1.2. Sanicula europaea - Abies cephalonica community.. 120 3.5.1.3. Syntaxonomic synopsis of the fir forests in the study area........................... 120 3.5.2. Vegetation units along the drought gradient.......... 121 3.5.3. Threshold values of the components of drought........ 122 A. Appendix 145 A.1. Climatic data............................... 146 iii Contents A.2. Climatic maps............................... 155 A.3. Statistics.................................. 158 A.3.1. MRPP............................... 158 A.3.1.1. Between groups A and B................ 158 A.3.1.2. Between sub-groups A1 and A2............ 158 A.3.1.3. Between sub-groups B1 and B2............ 158 A.3.2. PERMANOVA.......................... 159 A.3.2.1. Between groups A and B................ 159 A.3.2.2. Between sub-groups A1 and A2............ 159 A.3.2.3. Between sub-groups B1 and B2............ 159 A.4. Boxplots.................................. 160 A.5. NMDS................................... 164 A.5.1. NMDS graphs with isolines................... 164 A.5.2. Fits of environmental vectors and factors onto NMDS..... 173 A.6. R Functions................................ 174 A.6.1. Quantification of drought.................... 174 A.6.2. Vegetation analysis........................ 176 A.6.2.1. Cluster analysis..................... 176 A.6.2.2. Gradient analysis (ordination)............. 177 A.6.2.3. Classification tree.................... 177 A.7. Vegetation table.............................. 178 A.8. Species list................................. 186 iv Acknowledgments Many people have contributed to the completion of this work, from the very begin- ning to the last day of the submission. Without the help of all of them this thesis would have still been an unaccomplished dream. First of all I have to thank my two supervisors Albert Reif and Kostas Theodoropoulos, two wonderful persons that I had the good luck to meet in my life. Thanks to Kostas, my mentor over the first years of my scientific steps, I came into contact with the field of phytosociology. Thanks to Albert I did a step further into the field of vegetation ecology. I am grateful to both of them for their scientific support but I am also deeply indebted for all their non scientific help, whenever I need it. Albert I still owe you a luxurious dinner... I feel extremely grateful to Stefanie Gärtner for her crucial support at the beging and at the end of my PhD. Her critical spirit was always a good advisor. I should gratefully acknowledge Nikos Alexandris for helping a lot with the climatic analy- sis. His very good knowledge about GIS and his passion for the free/open source world made me see the things from another point of view, more open and more free. Grateful thanks are due to the following people for their help in my field work: Bernd Künemund, Rodrigo Vargas, Cristabel Durán, Osvaldo Vidal and Carl Höcke. I would like to acknowledge the help of Stefanie Gärtner, Rodrigo Vargas, Hendrik Stark, Juana Palma, David Forrester and Nathan Briggs for checking and correcting parts of my manuscript. Special thanks to Günter Gottschlich for verifying or iden- tifying specimens of the difficult genus Hieracium and Michael Lüth for identifying all the bryophytes. I would also like to express my gratitude to Christina Petschke for her guidance and help during the soil analysis in the Institute