This book would never have been finished if it were not for the many colleagues and friends who have been willing to give me the time and benefit of their specialist knowledge. I am especially grateful to colleagues who have read particular chapters, Professor R.J. Abbott (St Andrews), Professor R. Brändle (Berne), Professor F.-K. Holtmeier (Münster), Professor Ch. Körner Bale, Professor D. Tomback (Colorado), Dr L. Nagy (Glasgow), Professor S. Payette (Quebec) and Dr C. Vassiliadis (Paris). They may have saved me from error; if not, the fault is entirely mine. Many others have provided invaluable help in sourcing data and providing illustrations from all corners of the globe.

I am particularly grateful for detailed documentation as well as access to extensive collections of images from distant places to Professor R. Cormack (St Andrews), Dr A. Gerlach (Oldenburg), Professor F.-K. Holtmeier (Münster), Professor R. Jefferies (Toronto), Dr L. Nagy (Glasgow), and Professor J. Svoboda (Toronto). The privilege of using these images is acknowledged in the legends.

My own opportunities for studying plants in different parts of the world have been greatly aided by generous assistance from the Natural Environment Research Council, the Carnegie Trust for the Universities of Scotland, the Leverhulme Foundation and the Erskine Trust of the University of Canterbury (New Zealand).

This work would never have been undertaken had it not been for the stimulation and encouragement provided by the Cambridge University Press and I am particularly indebted to Dr Alan Crowden for the initial imaginative prompting that made me attempt this task, and to Dr Dominic Lewis and the production staff for bringing it to completion.

Part I

The nature of marginal areas

Fig. 1.1 A marginal population of mountain pine (Pinus mugo) colonizing stabilized scree slopes in the Vercors Regional National Park (France).

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