UNIVERSITÉ DE GENÈVE FACULTÉ DES SCIENCES Institut F.-A. Forel Professeur W. Wildi UNIVERSITÉ DE BERNE Professeur B. Ammann Institut of Plant Science ________________________________________________________________________________ Long Term Dynamics of the Vegetation at the Subalpine-Alpine Ecocline during the Holocene: Comparative Study in the Aletsch Region, Val D’Arpette, and Furka Pass (Valais, Switzerland) THÈSE présentée à la Faculté des sciences de l’Université de Genève pour obtenir le grade de Docteur ès sciences, mention interdisciplinaire par Adriana L. CARNELLI (Italie) Thèse N° 3378 GENÈVE Atelier de reproduction de l’école de Physique 2002 TABLE OF CONTENTS RESUME...................................................................................................................................... VII ABSTRACT...................................................................................................................................XX REMERCIEMENTS................................................................................................................... XXI CHAPTER 1: INTRODUCTION....................................................................................................1 1.1 THE SUBALPINE-ALPINE ECOCLINE ............................................................................................. 1 1.2 FUNCTIONAL AND ECOLOGICAL EXPLANATIONS FOR TREELINES ................................................ 1 1.3 PAST TREELINE FLUCTUATIONS ................................................................................................. 3 1.4 HUMAN PREHISTORIC POPULATIONS IN THE VALAIS AND NEIGHBOURING REGIONS..................... 5 1.5 AIM OF THE STUDY .................................................................................................................... 8 1.6 CITED REFERENCES.................................................................................................................... 9 CHAPTER 2: SITE DESCRIPTIONS AND METHODS OF INVESTIGATIONS...................13 2.1 SITE LOCATION........................................................................................................................ 13 2.2 CLIMATE.................................................................................................................................. 18 2.3 PRESENT VEGETATION DESCRIPTION........................................................................................ 19 2.4 METHODS OF INVESTIGATIONS ................................................................................................ 20 2.4.1 Soil analysis.....................................................................................................................20 2.4.2 Biogenic silica analysis....................................................................................................20 2.4.3 Charcoal analysis ............................................................................................................23 2.4.4 Pollen and plant macrorest analysis ..............................................................................23 2.4.5 Vegetation analysis..........................................................................................................24 2.4.6 Dendrochronological analysis.........................................................................................24 2.5 CITED REFERENCES.................................................................................................................. 25 CHAPTER 3: SUBALPINE AND ALPINE SOILS .....................................................................27 3.1 INTRODUCTION........................................................................................................................ 27 3.2 METHODS ................................................................................................................................ 29 3.3 RESULTS.................................................................................................................................. 30 3.4 DISCUSSION............................................................................................................................. 33 3.5 CONCLUSIONS ......................................................................................................................... 34 3.6 CITED REFERENCES.................................................................................................................. 35 CHAPTER 4: BIOGENIC SILICA IN PLANTS AND SOILS AT THE SUBALPINE-ALPINE ECOCLINE ...................................................................................................................................37 4.1 BIOGENIC SILICA PRODUCTION IN SELECTED ALPINE PLANT SPECIES AND PLANT COMMUNITIES .............................................................................................................38 4.1.1 ABSTRACT............................................................................................................................ 38 4.1.2 INTRODUCTION..................................................................................................................... 39 4.1.3 METHODS ............................................................................................................................. 42 4.1.3.1 Site descriptions............................................................................................................42 4.1.3.2 Collection of plant material and silica extraction.........................................................42 4.1.3.3 Light microscopy...........................................................................................................43 4.1.3.4 Estimate of the biogenic silica input into the soil..........................................................45 4.1.4 RESULTS............................................................................................................................... 46 4.1.4.1 Monocotyledons............................................................................................................46 4.1.4.2 Dicotyledons .................................................................................................................46 4.1.4.3 Conifers.........................................................................................................................47 4.1.4.4 Estimate of biogenic silica input into the soil................................................................48 4.1.5 DISCUSSION.......................................................................................................................... 50 4.1.5.1 Monocotyledons............................................................................................................50 4.1.5.2 Dicotyledons .................................................................................................................51 4.1.5.3 Conifers.........................................................................................................................52 4.1.5.4 Input and durability of biogenic silica particles in the soil...........................................55 4.1.6 CONCLUSIONS AND SUGGESTIONS FOR FUTURE RESEARCH ................................................... 57 4.1.7 ACKNOWLEDGMENTS............................................................................................................ 58 4.1.8 CITED REFERENCES .............................................................................................................. 58 4.2 PHYTOLITH TYPOLOGIES AND FREQUENCIES IN SUBALPINE-ALPINE PLANT SPECIES OF THE EUROPEAN ALPS .......................................................................................63 4.2.1 ABSTRACT............................................................................................................................ 63 4.2.2 INTRODUCTION..................................................................................................................... 64 4.2.3 METHODS ............................................................................................................................. 65 4.2.3.1 Laboratory procedures and samples.............................................................................65 4.2.3.2 Cluster analysis and principal components analysis (PCA)..........................................66 4.2.4 TYPOLOGY DESCRIPTIONS AND FREQUENCIES....................................................................... 68 4.2.4.1 Monocotyledons ...........................................................................................................68 4.2.4.2 Gramineae ....................................................................................................................71 4.2.4.3 Cyperaceae ...................................................................................................................72 4.2.4.4 Dicotyledons .................................................................................................................73 4.2.4.5 Conifers.........................................................................................................................75 4.2.4.6 Clustering analysis and PCA ........................................................................................81 4.2.5 DISCUSSION.......................................................................................................................... 85 4.2.5.1 Monocotyledons............................................................................................................85 4.2.5.2 Dicotyledons