Pollen evidence for Holocene climate change in the Eglinton Valley, western Southland Bronwyn van Valkengoed A thesis submitted in fulfilment of the requirements of Master of Science in Geography at the University of Otago, Dunedin, New Zealand. March 2011 In loving memory of Grandad Fowler and Opa van Valkengoed Memories of you will always be with me xoxox Abstract Numerous palaeoclimatic investigations have been undertaken throughout New Zealand in an attempt to reconstruct the vegetation and climatic history of the Holocene (10,000 yr B.P. to present). It is surprising therefore, that to date no detailed investigations have been undertaken in western Southland; one of New Zealand’s most climatically sensitive areas. Pollen analysis was undertaken on a 450 cm (5,030 ± 20 year old) peat core extracted from Eglinton Bog, western Southland, to reconstruct the mid to late Holocene vegetation and climatic history of this area. By 2,300 yr B.P. Nothofagus Fuscospora had expanded throughout the Eglinton area and by ~ 1,000 yr B.P. a species poor N. fusca/ Nothofagus solandri var. cliffortioides forest had largely replaced the pre-existing N. menziesii forest. The transition is believed to be associated with the further deterioration of the mid to late Holocene climate to the cooler, wetter, frostier and cloudier climatic conditions that dominate the area today. Using evidence from Eglinton Bog as a starting point a detailed integrated regional comparison of southern New Zealand’s Holocene vegetation and climatic history was established by comparing individual site elevation, mean annual temperature and precipitation, and pollen records. A regional expansion of N. menziesii and N. Fuscospora was recorded throughout southern New Zealand between approximately 5,000 – 1,500 yr B.P. However, the timing, rate of change and extent that species became dominant varied between locations. It is suggested that while climate change was the main forcing factor behind the transition from tall Podocarp forest to N. menziesii forest, and eventually N. Fuscospora; for the vast majority of southern New Zealand, the variation in the rate, timing and magnitude of the species expansion between different locations within southern New Zealand appears to have also been influenced by a combination of site specific variables including local climatic conditions, altitude, the absence of refugia, fire frequency and the symbiotic relationship between Nothofagus roots and fungi. i Acknowledgments To all of the people who assisted, encouraged, guided and helped me throughout the course of my studies, I wish to express my gratitude and sincere thanks. In particular I would like to thank: My supervisor Associate Professor Sean Fitzsimons for your direction and guidance throughout, especially towards the end. I know it didn’t make for pleasant bed time reading. And for the experience of a life time. Jamie Howarth for your patience, guidance and hours spent teaching me the ways of Pollen Analysis, helping identify unknown pollen types, discussing the many issues that arose, and your generally approachability over the last year. Your help and advice has not gone unappreciated and I am greatly indebted to you! N.B. “At some point you have to stop being a perfectionist and make decisions” All the best with your PhD. (Dr) Sarah Mager for your pep talks, guidance and editing skills not only over the course of this thesis but throughout my undergraduate study as well, especially hideous fourth year. You are right Masters is way easier. Julie Clark for your assistance in the laboratory. Sorry about the flood. David McDowell and Nigel McDonald for your computer genius and help with equipment. Marcus Vandergoes for your help identifying unknown pollen types and John Steel for your help keying out and identify plant species. Todd Redpath for your patience while teaching me ArcGIS and your handy tips. The Department of Conservation for allowing me access to Eglinton Bog. All the guys and girls in the Department of Geography who have helped me over the years. Dana and Kath for the walks and talks about life, and for being sounding boards throughout university life. Mum and Dad for your pep talks and support throughout my 5.3 years at varsity. For your belief in me and that I was actually doing something at university other than eating my lunch. A special thanks to Mum for your special cards which helped keep the junk draw stocked, and lugging the GPR up the 14 m high hill while fighting off sand flies. To Dad for your pep talks at 10.30 pm, car advice and hugs. Last but not least, my dearest Slade for your reassurance, belief and support of me throughout the year. Thank you for your patience, understanding, wicked sense of humour and love of all things unhealthy. ii Table of Contents Abstract ...................................................................................................................................... i Acknowledgments ..................................................................................................................... ii Table of Contents ...................................................................................................................... iii Table of Figures ......................................................................................................................... vi Table of Tables ........................................................................................................................ viii 1 Introduction ...................................................................................................................... 1 2 Vegetation history of New Zealand ................................................................................. 4 2.1 The vegetation history of New Zealand .................................................................. 4 2.1.1 LGM to Holocene Vegetation History of New Zealand......................................... 4 2.1.2 LGM to Holocene Vegetation History of Southern New Zealand ....................... 13 2.2 Summary ................................................................................................................. 23 2.3 Research objectives................................................................................................. 25 3 Methodology and Field Area ........................................................................................ 26 3.1 Introduction ............................................................................................................ 26 3.2 Research Strategy ................................................................................................... 26 3.2.1 Pollen analysis ...................................................................................................... 27 3.2.2 Assumptions and Limitations of Pollen Analysis ................................................ 27 3.2.3 Pollen preservation ............................................................................................... 29 3.2.4 Peat deposits as a preservation medium ............................................................... 29 3.3 Field Area ................................................................................................................ 31 3.3.1 Regional setting .................................................................................................... 31 3.3.2 Study Area ............................................................................................................ 33 3.4 Field Methods .......................................................................................................... 39 3.4.1 Ground Penetrating Radar .................................................................................... 39 3.4.2 Peat coring for pollen analysis ............................................................................. 39 iii 3.4.3 Vegetation surveying ............................................................................................ 41 3.5 Laboratory methods ............................................................................................... 41 3.5.1 Pollen analysis ...................................................................................................... 41 3.5.2 Radiocarbon dating ............................................................................................... 47 4 Results .............................................................................................................................. 48 4.1 Introduction ............................................................................................................ 48 4.2 Vegetation composition of Eglinton Bog .............................................................. 48 4.3 Geomorphology of the Eglinton Bog ..................................................................... 49 4.4 Stratigraphy and chronology of the pollen core .................................................. 51 4.5 Pollen Analysis ........................................................................................................ 54 4.5.1 Pollen diagram biostratigraphy ............................................................................. 54 4.5.2 Zone 1 (450 – 295 cm) ......................................................................................... 54 4.5.3 Zone 2 (295 – 195 cm) ......................................................................................... 56 4.5.4 Zone 3 (195 – 75 cm) ..........................................................................................