The Dendroclimatology of Modern and Neolithic Scots Pine (Pinus Sylvestris L.) in the Peatlands of Northern Scotland
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The dendroclimatology of Modern and Neolithic Scots pine (Pinus sylvestris L.) in the peatlands of northern Scotland A thesis submitted for the degree of Doctor of Philosophy by Andrew Kevin Moir Institute for the Environment Brunel University September 2008 Abstract For the first time in northern Scotland, Modern tree-ring chronologies for Scots pine growing on peat are compared against those growing on mineral substrates. Mean tree-ring growth of pine on active bogs/mires is found to be limited to 0.5 to 1 mm yr-1, compared to ≥1.5 mm yr-1 on adjacent mineral sites. Almost instant change of radial growth rates in response to changes in water levels highlights the potential use of pine in reconstructions of lake levels and water tables in bog and mire. Dendroclimatological analysis identifies January and February temperatures to often be more important than summer temperature. Positive correlation of ring-width and North Atlantic Oscillation (NAO) indices also occur in January and February. Lower winter temperatures, due to increased altitude and distance from the moderating effects of the ocean, may be important in limiting tree growth near its northern margin. Moving correlation functions identify a widespread reduction in the response of pine growing on both substrates from the 1920s. Nine subfossil pine site chronologies located beyond the species current northern limit are cross-matched to form a chronology called WRATH-9. This chronology is tentatively crossdated against Irish pine chronologies to provide the first picture of Neolithic Scots pines 200 year expansion from c. 3200 BC and subsequent 250 year retreat across northern Scotland at annual resolution. The mean orientation of maximum radial growth at eleven modern pine sites is found to coincide well with the W/SW prevailing wind, suggesting Scots pine may provide a good proxy indicator of wind. Six coeval Neolithic sites indicate a broadly consistent northerly prevailing wind. This provides tentative evidence for a change of prevailing wind that may be related to a southward incursion of the polar front in the eastern N. Atlantic. The potential of this exciting subfield of dendroclimatological analysis is called dendroaeology and is highlighted for further research. i Acknowledgements The intensive fieldwork in the summer of 2004 (during which the vast majority of Holocene subfossil pine were sampled) would not have been possible without the kind assistance of family - Capt. Brian Moir, Rose Moir, Sandy Moir and Glen Shields. I am grateful to people in north Scotland for their kind permission to access their land and conduct sampling, these include: Michael Wiggen (Loch Ascaig), Douglas Mainland (Assynt Estate, Loch Assynt), James Clark (Eriboll Estate, Loch Eriboll), Angus Ross (Achentoul Estate, Loch an Raithair) and Kate Holl & Eoghain Maclean (Scottish National Heritage, Eilean Sùbhainn). I gratefully acknowledge the Quaternary Research Association for a grant which funded part of this fieldwork. I am indebted to Russell Anderson (Forestry Commission) who saved me a huge amount of time and effort and allowed me to increase the scope of this study by granting permission to measure modern pine samples collected as part of a previous study on the bogs of: Abernethy, Inshriach, Monadh Mor and Pitmaduthy Moss. John Grace (University of Edinburgh) and David Norton (University of Canterbury, New Zealand) kindly provided me tree-ring data for their Creag Fhiaclach and Carrbridge sites, also Coralie Mills (AOC Archaeology) for data from Ballochbuie. Particular thanks go to John Daniel (University of Gloucestershire), David Brown (Queen’s University of Belfast) and Hubert Leuschner (University of Göttingen) who provided Holocene pine reference chronologies. I am grateful to Cathy Groves (Sheffield University) and Samuli Helama (University of Helsinki) for running the WRATH-9 chronology against available Holocene pine and oak reference chronologies. David Brown also very kindly 14C dated two of the pine samples, which was invaluable. Finally I would like to express my gratitude to Prof. Suzanne Leroy and Dr Phil Collins, my supervisors at Brunel University, for their advice and support during this project. To Steve Jebson and Hazel Clement (Met Office) and Phil Jones and David Lister (University of East Anglia) for access to climate data. Petr Stepanek (Masaryk University) kindly undertook analysis of rainfall data and made available his PROCLIMDB & ANCLIM software. ii 1 INTRODUCTION .........................................................................................................1 1.1 Modern Scots pine ..................................................................................................3 1.1.1 Geographic location...........................................................................................3 1.1.2 Caledonian Pine Forest......................................................................................3 1.1.3 The ranges of Scots pine in Scotland .................................................................4 1.1.4 Natural regeneration...........................................................................................6 1.1.5 Disturbance of native pinewood.........................................................................7 1.1.6 Genetics and genetic local adaptation................................................................8 1.1.7 Pine trees growing on bog..................................................................................9 1.2 Holocene Scots pine in the peatland archive of Northern Scotland.................10 1.2.1 The relationship between peatland and climate ...............................................11 1.2.2 Problems of temporal resolution......................................................................13 1.2.3 The preservation of Holocene subfossil pine...................................................15 1.2.4 The early history of Scottish pinewoods..........................................................17 1.2.5 A 3500-2300 14C cal. yr BC northward expansion of Scots pine ....................18 1.2.6 Changes in the elevation of pine ......................................................................20 1.2.7 The pine decline 2000 14C cal. yr BC ..............................................................20 1.3 The dendrochronology of Scots pine...................................................................21 1.3.1 Dendroclimatology in Scotland.......................................................................21 1.3.2 X-ray microdensitometry .................................................................................23 1.3.3 Changing Signals.............................................................................................23 1.3.4 Wind and North Atlantic Oscillation ...............................................................24 1.3.5 Holocene pine..................................................................................................26 1.3.6 Holocene subfossil pine chronologies..............................................................26 1.4 Aims & Objectives ................................................................................................27 2 METHODS...................................................................................................................28 2.1 Dendrochronological analysis..............................................................................28 2.1.1 Sample size......................................................................................................28 2.1.2 Site selection criteria........................................................................................29 2.1.3 Sampling and preparation ................................................................................29 2.1.4 Measuring.........................................................................................................30 2.1.5 Tree-ring reference data ...................................................................................30 2.1.6 Cross-matching ................................................................................................31 2.1.7 Removal of growth trend and physiological preconditioning..........................32 2.1.8 The descriptive statistics of standardised chronologies ...................................34 2.2 Stand Dynamics ....................................................................................................35 2.2.1 Growth trend sequences based on the biological age of trees..........................35 2.2.2 The use of pith and bark in tree aging..............................................................36 2.2.3 Patterns of regeneration ...................................................................................37 2.2.4 A possible relationship between radial growth and prevailing wind ...............37 2.2.5 Peat/root depth, orientation and stump height .................................................39 2.2.6 Scars .................................................................................................................40 2.3 Climatic Data ........................................................................................................41 2.3.1 Rainfall.............................................................................................................42 2.3.2 Temperature .....................................................................................................42 2.3.3 Sunshine ...........................................................................................................42