Epiphyte Communities and Indicator Species an Ecological Guide for Scotland’S Woodlands

Epiphyte Communities and Indicator Species An Ecological Guide for Scotland’s Woodlands Christopher J. Ellis I Sally Eaton I Marios Theodoropoulos I Kathryn Elliott Epiphyte Communities and Indicator Species An Ecological Guide for Scotland’s Woodlands ISBN 978-1-910877-01-2 © Royal Botanic Garden Edinburgh, 2015 Photo credits as listed in the acknowledgements. The Royal Botanic Garden Edinburgh (RBGE) is a Non Departmental Public Body (NDPB) sponsored and supported through Grant-in-Aid by the Scottish Government’s Environment and Forestry Directorate (ENFOR). The Royal Botanic Garden Edinburgh is a charity registered in Scotland (number SC007983). All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted, in any form, or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written consent of the copyright holders and publishers. Design and layout: Helen Meek Christopher J. ELLIS, Sally EATON, Marios THEODOROPOULOS and Kathryn ELLIOTT (2015) Epiphyte Communities and Indicator Species. An Ecological Guide for Scotland’s Woodlands. Royal Botanic Garden, Edinburgh. Contents Acknowledgements Preface Chapter 1 1 Introduction Chapter 2 19 Epiphyte Sampling Chapter 3 25 Woodland Habitat for Epiphytes Chapter 4 34 Epiphyte Community Classification Chapter 5 41 Exploratory Ecological Analysis Appendix 1 98 List of Species Associated with Epiphyte Community Types Appendix 2 111 Epiphyte Community Comparison with James et al. (1977) Appendix 3 116 Pro Forma for the Field Recording of Epiphyte Communities Appendix 4 121 Calculation of Habitat Heterogeneity and Biodiversity End Notes 124 References 130 Acknowledgements The work presented in this report was made possible by a grant received from the Esmée Fairbairn Foundation. The report has benefited from support provided by many people in various different ways, though in particular Dr David Bell and Dr Brian Coppins (Royal Botanic Garden Edinburgh) for help in determining some of the most difficult bryophyte and lichen specimens, respectively, Dr Rebecca Yahr (Royal Botanic Garden Edinburgh) for the identification of Usnea specimens, and Dr David Genney (Scottish Natural Heritage) for guidance in the safe sampling of rare species. We thank staff at Scottish Natural Heritage regional offices and the landowners of the field sites for advice, logistics and in providing access for epiphyte sampling. Dr Brian Coppins generously provided his expert opinion on the statistical recognition of epiphyte Community Types compared against field experience. Thanks also go to Mr Matthew Haughton for assisting with chemical analysis of bark and soil, and to Dr Toby Pennington (Royal Botanic Garden Edinburgh) and Dr Mark Watson (Royal Botanic Garden Edinburgh) for their help in sourcing images of non-British epiphytes. All photo credits belong to the authors (Sally Eaton and Christopher Ellis), with the exception of: Figure 1.2 (Mark Watson) and Figure 1.3A (Toby Pennington). We thank Rebecca Yahr for editing and proof-reading drafts of the manuscript, and Brian and Sandy Coppins, David Genney and Frances Stoakley for their helpful suggestions and improvements. Preface This report presents the variability of epiphyte communities in native British woodland, explores the environmental factors that control them, and provides a framework for their identification using indicator species. As far as is possible, the underpinning research was for epiphyte communities which remain intact, and for this reason it was concentrated in northern Scotland. This is a region for which, relatively speaking, the air quality has been less affected by industrial emissions, and land management is less intensive. On this basis, the report provides an introduction to Scotland’s internationally important epiphytes. Epiphytes are important in many ways. First, their physical presence and diversity remind us that a forest or woodland is more than the sum total of its trees, becoming an ecosystem of multi-layered complexity. This links to the growing awareness within conservation that a multitude of small organisms, including bryophyte and lichen epiphytes, contribute importantly to the structure and function of healthy ecosystems. Second, epiphytes are of immense cultural significance. They are indicators of clean air and provide a warning of the negative impacts of pollution on human health, and they provide a sense of place with nature. Learning to discriminate between some simple epiphyte species and communities makes it possible to orientate and understand a woodland biogeographically, for example by recognising a globally rare temperate rainforest, such as on Scotland’s west coast, or a Boreal-type system allied with Scandinavian forests, such as in the higher altitude reaches of Strathspey. It also becomes possible to recognise woodlands of special interest, such as those with long ecological continuity that are biodiversity hotspots. This report aims to have a wide appeal. In general terms, the introductory material will increase awareness of the biodiversity importance and cultural value of Scotland’s epiphytes, providing an impetus for their protection. More specific suggestions of use are provided below: l By recording species indicators for different community types the conservationist or forest/woodland manager can gather information showing the effect of habitat heteorogeneity (variability) on species diversity; more heterogeneous habitats will be represented by a greater range of community types. l For the natural historian with some basic knowledge of bryophytes and lichens, the report can suggest focal species for field recording as part of their enjoyment of the natural world, in contribution to data gathering for monitoring, and as a framework for building further knowledge. l For the ecologist it provides a summary of community-level information specific to epiphytes, and these field sampled data are the background from which to develop new questions for primary research. l For the experienced lichenologist it provides a systematic epiphyte survey and ecological analysis with which to compare and contrast tried-and-tested concepts such as the ‘Graphidion’ or ‘Lobarion’ phytosociological communities, coupled with quantitative information on the variability of environmental conditions experienced by epiphytes in Scotland in the early 21st Century. For those who wish to learn more, the Royal Botanic Garden Edinburgh provides introductory courses in bryophytes and lichens, while the Field Studies Council partners with specialist biologists to support identification training relevant to epiphytes. In addition, the British Bryological Society and British Lichen Society are the academic societies which support an interest in bryophytes (mosses and liverworts) and lichens through publications, field excursions and a programme of meetings and workshops for all abilities. It is our hope that readers of this report will either discover for the first time, or reappraise their knowledge of Scotland’s globally significant epiphytic diversity, and help to secure its future conservation. Introduction Epiphyte Communities and Indicator Species 1m CHAPTER Introduction Epiphyte: ‘A plant which uses another plant, typically a tree, for its 1 physical support, but which does not draw nourishment from it’ The Oxford Dictionary of Botany. 1.1 The Nature of Epiphytes Epiphytes grow on the bark surface of trees, taking advantage of the physical support offered by trunk, branches and twigs as these reach upwards above the ground. They are photosynthetic organisms, which means that they produce their own food using energy from sunlight and basic raw materials (carbon dioxide, water, and nutrients), and they do not parasitise the tree on which they grow. Rather, epiphytes use trees as a scaffold, and this has proven to be an ingenious and ecologically successful strategy. Forests cover approximately 30% of the global land surface (4 billion hectares)1 and an individual tree such as an oak, with a modest girth of 2 metres, has a bark surface area that is at least 74 times greater than the ground space it occupies2. Considered across forests globally, the accumulated surface area provided by a vast number of trees represents an extensive habitat to which epiphytes are adapted (Figure 1.1). Figure 1.1. A. Forests cover huge areas of the terrestrial Figure 1.1. B. Beneath the forest canopy, at the scale of land surface, as here in the densely forested southern the individual tree, an interwoven structure of trunks and Appalachian mountains of Georgia (USA). branches provides an extraordinary surface area of bark for colonisation by epiphytes. By growing on the outer surface of structurally dominant trees, epiphytes avoid competition for space and the limitations of shading in the ground layer of forests; however, epiphytes must overcome the difficulties associated with an existence away from the soil environment, including restricted access to water, leading to periods of desiccation, and limited availability of essential nutrients3. Nevertheless, a tremendous diversity of plants and fungi is adapted to the epiphytic environment and can be found in forests across the planet forming an above-ground ecosystem of awe-inspiring complexity (Figure 1.2). Epiphytes are a visible reminder that a forest is comprised of more than trees, which create the obvious structure. Forty percent of all known terrestrial species are associated with forest canopies,

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