THE SILVICULTURE OF TREES USED IN BRITISH FORESTRY, 2ND EDITION This page intentionally left blank The Silviculture of Trees Used in British Forestry, 2nd Edition Peter Savill Former Reader in Silviculture University of Oxford With illustrations by Rosemary Wise CABI is a trading name of CAB International CABI CABI Nosworthy Way 38 Chauncey Street Wallingford Suite 1002 Oxfordshire OX10 8DE Boston, MA 02111 UK USA Tel: +44 (0)1491 832111 Tel: +1 800 552 3083 (toll free) Fax: +44 (0)1491 833508 Tel: +1 (0)617 395 4051 E-mail: [email protected] E-mail: [email protected] Website: www.cabi.org © Peter Savill 2013. All rights reserved. No part of this publication may be reproduced in any form or by any means, electronically, mechanically, by photocopying, recording or otherwise, without the prior permission of the copyright owners. A catalogue record for this book is available from the British Library, London, UK. Library of Congress Cataloging-in-Publication Data Savill, Peter S. The silviculture of trees used in British forestry / Peter Savill. -- 2nd ed. p. cm. Includes bibliographical references and index. ISBN 978-1-78064-026-6 (alk. paper) 1. Forests and forestry--Great Britain. 2. Trees--Great Britain. I. Title. SD391.S285 2013 634.90941--dc23 2012043421 ISBN-13: 978 1 78064 026 6 Commissioning editor: Vicki Bonham Editorial assistants: Emma McCann and Alexandra Lainsbury Production editor: Lauren Povey Typeset by SPi, Pondicherry, India. Printed and bound in the UK by the MPG Books Group. Contents Acknowledgements viii Introduction 1 ABIES 10 ALBA 10 GRANDIS 12 PROCERA 15 ACER 18 CAMPESTRE 18 PLATANOIDES 19 PSEUDOPLATANUS 23 ALNUS 29 CORDATA 29 GLUTINOSA 31 INCANA 36 RUBRA 37 ARIA 39 NIVEA 39 BETULA 41 PENDULA 41 PUBESCENS 41 BUXUS 48 SEMPERVIRENS 48 CARPINUS 52 BETULUS 52 CASTANEA 55 SATIVA 55 CEDRUS 60 ATLANTICA 60 LIBANI 62 CHAMAECYPARIS 65 LAWSONIANA 65 CORYLUS 69 AVELLANA 69 v vi Contents CRYPTOMERIA 72 JAPONICA 72 x CUPROCYPARIS 75 LEYLANDII 75 EUCALYPTUS 77 FAGUS 81 SYLVATICA 81 FRAXINUS 88 EXCELSIOR 88 ILEX 95 AQUIFOLIUM 95 JUGLANS 98 NIGRA 98 REGIA 101 LARIX 108 DECIDUA 108 KAEMPFERI 110 x MARSCHLINSII 110 MALUS 116 SYLVESTRIS 116 NOTHOFAGUS 119 ALPINA 119 OBLIQUA 119 PICEA 123 ABIES 123 SITCHENSIS 126 PINUS 132 CONTORTA 132 MURICATA 136 NIGRA 137 NIGRA ssp. NIGRA 140 NIGRA ssp. SALZMANNII 140 PEUCE 143 RADIATA 145 STROBUS 147 SYLVESTRIS 147 POPULUS 151 HYBRID 151 Contents vii NIGRA 156 TREMULA 157 PRUNUS 161 AVIUM 161 PSEUDOTSUGA 167 MENZIESII 167 QUERCUS 171 CERRIS 171 PETRAEA 173 ROBUR 173 RUBRA 186 ROBINIA 189 PSEUDOACACIA 189 SALIX 193 SEQUOIA 198 SEMPERVIRENS 198 SEQUOIADENDRON 201 GIGANTEUM 201 SORBUS 205 AUCUPARIA 205 TAXUS 208 BACCATA 208 THUJA 214 PLICATA 214 TILIA 218 CORDATA 218 PLATYPHYLLOS 223 TORMINARIA 225 TORMINALIS 225 TSUGA 229 HETEROPHYLLA 229 ULMUS 234 GLABRA 234 PROCERA 236 References 239 Key 257 Index 269 Acknowledgements I am grateful to many colleagues and generations of students at Oxford University who have contributed, in various ways, to the preparation of this book by their insights and by referring me to relevant papers in journals and elsewhere. I am especially indebted to Rosemary Wise who produced all the drawings. Jo Clark, Gabriel Hemery, Andrew Leslie, Jens-Peter Skovsgaard of the Swedish University of Agricultural Sciences, Valeriu-Norocel Nicolescu of Brasov University, Romania, John Fennessy of COFORD in Dublin, Gary Kerr from Forest Research and Jürgen Huss of Freiburg University all provided detailed information on various spe- cies. Michelle, my wife, has undertaken the tedious job of reading through and checking all the text. John Baker kindly photographed the leaves used to illustrate the key. Colleagues in four charities with which I have been associated for many years deserve particular acknowledgement: Woodland Heritage; the Royal Forestry Society of England, Wales and Northern Ireland; the Future Trees Trust; and the Earth Trust. Through my connections with them, I have been able to visit many of the most impressive woodlands in Great Britain and Ireland, and discuss silvicultural practices with their owners or managers. The figures in Table 1 were provided by Jackie Watson of the Economics and Statistics Branch of the Forestry Commission, and are reproduced with permission. The scientific names of the trees used in this book were kindly checked by Stephen Harris, Druce Curator of the Oxford University Herbaria. Several have changed since the first edition was produced in 1991. viii Introduction Many books have been written about trees that grow in Britain. They range from guides for identification to books that have been lavishly illus- trated by talented photographers and artists. One of the best known of the former group is Alan Mitchell’s (1974) A Field Guide to the Trees of Britain and Northern Europe and its successors, and among the latter is Thomas Pakenham’s (1996) Meetings with Remarkable Trees. Numerous publications by the Forestry Commission also provide much basic information that can be useful when selecting species for specific sites. Few books, however, cater particularly well for the person who seeks detailed information about the silvicultural characteristics and requirements of individual species. Among the authors to do this were M.L. Anderson in his Selection of Tree Species, which was first published in 1950, and Macdonald et al. (1957) in their Exotic Forest Trees in Great Britain. The information they provided about species, though still very useful, has inevitably become some- what dated as techniques have changed and knowledge has increased. More recently, Ray (2001) and Pyatt et al. (2001) have produced a computer-based ecological site classification that has proved invaluable in assisting the selection of species, as well as indicating how species might respond to climate change. It is based upon matching a four-climatic vari- able (accumulated temperature, moisture deficit, windiness and conti- nentality) and two soil variables (moisture and nutrient regimes) with the requirements of 31 possible species of tree. In addition, the shade tolerance of each species is taken into account. Yet computer programs, however sophisticated, can never substitute for educated and informed thinking, knowledge and understanding. © Peter Savill 2013. The Silviculture of Trees Used in British Forestry, 2nd Edn (P. Savill) 1 2 Introduction Matching species to site The climate of an area limits the range of species that can be grown suc- cessfully. Temperature, precipitation and wind are usually considered the important elements of climate for forestry. The more favourable the climate, the greater the range of species from which a choice can be made. In upland regions of Britain where the cli- mate is harsh and soils are often poor, the number is limited to two or three, whereas on good soils, in the better climate of the lowlands, a choice from about 20 may often be possible. These latter sites are said to have greater amplitude. Forestry has traditionally taken second place to agriculture, and most forest sites are marginal for agricultural production in some way. A large pro- portion of British forests are at high elevations where growing seasons are much shorter than in the lowlands and exposure to gales is common. Apart from physical problems such as steepness, stoniness and exposure, many forest soils tend to be drought-prone or waterlogged, suffer from extremes of acidity or alkalinity, or have compacted or cemented layers. Two-thirds of the state-owned forests have soils that suffer from poor aeration due to permanent or periodic waterlogging (Toleman and Pyatt, 1974). There are numerous important interrelationships between the physical, chemical and biological influences in a soil that can affect species choice. In many places today there is considerable past experience of which species will grow and how they will perform, either from existing stands of the same tree on the site itself, or from similar nearby areas. Site condi- tions should guide species choice in any approach to forest management, and this is particularly important for continuous-cover forestry given its demanding requirements in terms of stand stability, diversity, the use of natural processes and multipurpose management. Exceptional climatic events can reveal inadequacies in species selec- tion that may not be apparent in more normal periods. This is one rea- son why extreme caution should be observed before a relatively untried, but promising, exotic tree is planted on a wide scale. A common pattern with introductions everywhere is one of initial establishment in gardens and arboreta and then, if successful, perhaps half a rotation later, this is followed by small-scale planting on estates and by government depart- ments. Large plantations of the most promising species are established some 20–50 years after that (Streets, 1962). Thus, Sitka spruce, which is the major plantation tree in Great Britain and Ireland, was first introduced in 1831. It was established as one of the chief exotics in the early 1920s and by the mid-1950s it became the most widely planted tree. Premature extensive planting often leads to problems. For example, in Britain the cold winters of 1981−82 and 2010−11 killed many Eucalyptus spp. that were being tested experimentally, but at the same time they were also being promoted for widespread planting by a few people. Introduction 3 The general considerations that must be taken into account when deciding what to plant on a site are described in many silviculture text- books. The amount of information available about the climatic and site requirements of each species, and other features of their silviculture, var- ies considerably but is closely related to how common and important they are. For some, especially the major conifers, oak and beech, knowledge is quite comprehensive, while for others such as lime and walnut it is scanty and sometimes almost non-existent.