First and foremost I offer my sincerest gratitude to my supervisors, Richard Ennos, Glenn Iason and Chris Ellis, who have supported me throughout the duration of the PhD with their patience and knowledge, whilst allowing me the freedom to work in my own way. Each devoted a lot of time and energy to asking pertinent questions, holding discussions, identifying specimens, and keeping me on track in many other ways throughout the past few years. Without their help this thesis would not exist. The combination of the Institute of Evolutionary Biology (University of Edinburgh), the Royal Botanic Garden Edinburgh, and the James Hutton Institute (Aberdeen) have provided the support and equipment I have needed to produce and complete my thesis, and the BBSRC has funded my studies.

I have been aided in all things HPLC for the past few years Ben Moore – a fine and very patient scientist who kept me (and the HPLC) working, and in methanol, at all costs. The achievement in acquiring phenolic chemistry results is much more a testament to his skill than my own efforts tutoring me in the methods necessary to operate the HPLC/ ChemStation software, and how to analyse the copious amounts of data obtained. A special mention to Glenn’s team for lab assistance and friendly smiles – Sheila especially. I will be eternally grateful to Mark Brewer (BioSS) for providing me with some very practical guidance on (probably) the toughest statistics I have ever encountered so far, and for discovering why my residuals were especially appalling.

Ern and Val Emmett were instrumental in locating natural aspen stands. As well as being incredibly knowledgeable naturalists, they are also thoroughly kind people and have been wonderful hosts. Such qualities are rare these days, and I have greatly appreciated their conversation and company. Alas, the sauna will have to manage without me.

The use of aspen at Invertromie was authorized by Pete Moore (SNH Achantoul), Karen Sutcliffe and Pete Moore (RSPB Insh Marshes); the use of the experimental aspen clones at Moray and Kilmichael was authorized by Alan Harrison (Forest Research, Bush Estate) with permission from the landowners.

When not on fieldwork, in Aberdeen, or hiding at home to write this thesis, I have been greatly blessed with a smashing group of fellow PhD candidates. Garvin Sealy has been my rock from beginning to end. Little did he know at the time what he was letting himself in for, but he has taken the brunt of my frustrations on the chin. Always encouraging during the struggles, excited at the achievements, and keeping me well fed and watered. This PhD is as much his as it is mine. Finally, for Crumpet, whose gentle company kept me sane whilst writing; you will always be missed.