Forestry Commission Forestry Commission ARCHIVE Occasional Paper 26 Forest Bird Communities S J Petty M f Avery Number of bird species Pairs per knA 20-1 r500 h400 -300 v 5:V' :;■> VVA •« V '* • \ \ ■- '■ '.V%\ ’ 8- -200 4- -100 yv A a k A - - A ' A H i v-v Moorland Pole-stage forest FORESTRY COMMISSION OCCASIONAL PAPER 26 Forest Bird Communities A review of the ecology and management of forest bird communities in relation to silvicultural practices in the British uplands S.J. Petty Bird Ecologist, Forestry Commission cind M l. Avery Senior Research Biologist, Royal Society for the Protection of Birds, formerly Research Fellow, Edward Grey Institute of Ornithology, Oxford Forestry Commission, Edinburgh © Crown copyright 1990 First published 1990 ISBN 0 85538 237 6 ODC 148.2 : 152 : 2 : (048.1) KEYWORDS: Birds, Forestry Enquiries relating to this publication should be addressed to The Technical Publications Officer, Forestry Commission, Forest Research Station, Alice Holt Lodge, Wrecclesham, Farnham, Surrey GU10 4LH. Contents 1. Introduction 1 The need for a review 1 Acknowledgements 1 2. Historical aspects of forests and bird populations in the British uplands 3 Introduction 3 The development of plant communities in the Pleistocene period 3 Forests and birds in the Flandrian period 5 Summary 11 3. Bird census methods and techniques 12 Introduction 12 Choice of study areas 12 Census techniques 12 Diversity indices 13 V egetation description 14 4. Factors determining forest bird communities 17 Introduction 17 The ideal approach 17 Regional differences 18 Altitude 19 Forest area 19 Tree species 22 Succession 28 Vegetation structure 30 Edge effects 32 Summary 34 5. The effects of upland afforestation on birds in Britain 35 Introduction 35 Bird communities in relation to the growth stages of conifer forests 36 Threatened moorland birds 40 Regional differences 47 Afforestation 53 Concluding remarks 58 6. The current forest resource and its management 59 Introduction 59 The forest resource 59 Forest management 62 Hazards to forests in the uplands 68 Summary 70 7. Management of forest bird communities in the uplands 71 Introduction 71 Afforestation 71 Restructuring 84 Standing crop improvements 88 Summary 90 8. Future bird research in upland forests 91 Introduction 91 Comments on methods 91 Research recommendations 92 References 97 Chapter 1 Introduction The need for a review The review is aimed mainly at two groups. First, it will provide forest managers with information By the time of the formation of the Forestry on how bird communities function in a dynamic Commission in 1919 most native forests had forest environment and what foresters can do to been stripped from the British uplands, primar­ achieve a richer, better balanced avifauna ily by man, over a period of many centuries. This within their forest. Second, it will provide the process accelerated towards the time of the various conservation bodies with a background industrial revolution and once devoid of trees, to current forest practices in the uplands and the development of sporting interests and sheep how these are likely to affect birds. farming were essential to perpetuate the treeless The review has used literature from different character of many moorlands. This was achieved geographical regions. Chapters 2, 5, 6 and 7 are by a combination of heavy grazing and regular based mainly on British studies and practices burning which effectively prevented any natural while Chapters 3 and 4 use literature from the regeneration. By the turn of the 20th century, much larger Holarctic region (Figure 1.1). The less than 5 per cent of the land surface of Britain literature from these regions has been searched was forested, less than any other country in up to the end of 1986 although some studies mainland Europe. published in 1987-88 and in press have been Afforestation, mainly with exotic conifers used. The review is not intended to be a grown on relatively short rotations, has had a comprehensive account of all the published work dramatic effect on the landscape of many upland in a particular field. Chapters 2 and 6 are ‘scene areas over the last 50 years. Continued expan­ setters’ where the aim is to explain why our sion of forestry in the uplands (Centre for natural vegetation/wildlife communities and Agricultural Strategy, 1980; Forestry Commis­ forests are the way they are. The objective of sion, 1977) has led to concern being voiced for Chapters 3, 4, 5 and 7 was to be selective and the characteristic plant and animal communities critical and to use the most important papers associated with upland areas (Nature Conser­ published in scientific journals and books. vancy Council, 1986) together with aesthetic and Throughout we have tried to be objective and landscape objections. Much of this concern has unbiased. Chapters 3, 4 and 5 were written by focused on the effects of afforestation on bird MIA and Chapters 2, 6 and 7 by SJP. communities. A widely held view is that moor­ land birds with restricted range are replaced by more widely distributed forest birds (Nature Acknowledgements Conservancy Council, 1986; Thompson et al., Many people have helped with the preparation 1988). of this review and to these we are very grateful. It is therefore timely to review what has been Anabel Seddon helped by collating and key- published on the ecology and management of wording many of the earlier references, John forest bird communities and to relate this to Williams prepared the figures; Winifred Cooper, silvicultural practices in the British uplands. Diane Chadwick and Linda Petty undertook the 1 typing including numerous revisions. A number Bibby, Roderick Leslie, Phil Ratcliffe and Julian of people commented on, and greatly improved Evans, draft chapters: they were Ian Newton, Colin B= Western Palearctic F= Oriental B+C“ Palearctic G= Malagasy A+B+C= Holarctic H= Australasian D= Neotropical Figure 1.1 Zoogeographical regions of the world (redrawn from Pemberton, 1981). Regions are often separated by transitional zones and therefore the boundaries are approximations. 2 Chapter 2 Historical aspects of forests and bird populations in the British uplands Introduction period to another”. West (1968) describes methods for taking samples in the field, while The development of a number of techniques has both he and Faegri and Iversen (1964) give enabled paleoecologists to trace the development accounts of the microscopic identification and of the British flora not only since the last ice age counting of pollen. but also in the previous interglacial periods. Compared with what has been discovered These methods have relied largely upon the about past plant communities, very little is preservation of both macroscopic plant remains known about the species of birds previously (for example wood, seed and leaves) or microsco­ present let alone details of bird communities. pic (pollen) plant remains in rapidly accumulat­ Compared with mammal remains, bird bones ing organic or mineral deposits such as mires, are very fragile and there are few fossil remains. moor humus and lake sediments. The age of Most bird remains have been found in cave these remains has been determined either by deposits and archaeological sites. Bird remains radiocarbon dating or by relating the material to are also biased towards the larger species with the layers in which they were found. Godwin more substantial skeletons. From the few spor­ (1975) summarises most of the techniques that adic records of birds and a knowledge of plant have been used. Radiocarbon dating enables an communities, it is only possible to speculate on estimation of the age of material up to approxi­ the bird communities present in the British Isles mately 50000 years to be made. Radiocarbon prior to recent history. From AD 1600 the dates have been calibrated by using tree rings in literature becomes increasingly more valuable. long lived species such as coast redwood and bristle-cone pine (Suess, 1967; 1970). In this chapter all dates refer to radiocarbon years The development of plant before the present (BP). communities in the Pleistocene Pollen analysis has led to a great advance in our knowledge of past plant communities. There period are a number of potential problems associated Within the British Isles the Pleistocene period with the method, the major one is that pollen can has produced a number of glacial stages inter­ travel a great distance in certain weather condi­ spersed with periods of climatic amelioration. tions. Despite this and other analytical difficul­ The last three interglacials were the Hoxnian, ties, pollen analysis is now accepted as a valid Ipswichian and the present-day Flandrian (God­ method for determining the composition of for­ win, 1975). The latter commenced approxi­ mer plant communities. Godwin (1975) quoting mately 10000 years BP as the ice sheets from von Post, a pioneer of the system, stated that “by the Weichselian glaciation finally retreated establishing these frequency figures layer by northwards. Turner and West (1968) have sug­ layer through the pollen bearing strata it be­ gested that these interglacials showed a charac­ comes possible to follow former plant geographic teristic succession of plant communities which changes from place to place and from one time they divided into four periods. 3 1. Pre-temperate forest. Comprising boreal 4. Post-temperate forest. Climatic deterioration pioneers such as Betula and Pinus which leading to the re-appearance of Pinus and developed gradually after the last ice age. Betula. Soils becoming more acid and with an Light demanding species and herbs are also opening of the forest canopy leading to the a significant element of the vegetation. development of heath and bog communities 2. Early-temperate forest. A gradual improve­ prior to the next glaciation. ment of forest soils leading to the develop­ These of course are very broad divisions in a ment of mixed broadleaved forest with Quer- large timescale, for example the Hoxnian inter­ cus, Ulmus, Fraxinus and Corylus predomi­ glacial lasted for approximately 40 000 years nating.