Rhododendron ponticum: impact on lower plants and fungi communities on the west coast of Scotland. Deborah Long and Jill Williams Rhododendron ponticum: impact on lower plants and fungi communities on the west coast of Scotland. Working towards protecting internationally important bryophyte and lichen communities from Rhododendron ponticum invasion. Scottish Natural Heritage project no. 19412 July 2007 Revised version dated: November 2007 Deborah Long and Jill Williams Plantlife Scotland Balallan House Allan Park Stirling FK8 2QG 01786 478509 [email protected] www.plantlife.org.uk Contents 1 Geographic and ecological scope ..................................................................................... 1 2 Project objectives .............................................................................................................. 6 3 Element 1: Audit of rhododendron management work to date .......................................... 6 4 Element 2: Development of a draft list of sites known to be of high bryophyte and lichen interest that are threatened by R. ponticum invasion ........................................................ 9 5 Element 3: development of a rationale for site prioritisation............................................ 11 6 Element 4: Visits to priority lichen & bryophyte sites ....................................................... 11 6.1 Site selection ..................................................................................................................11 6.2 Survey method................................................................................................................15 7 Element 5: Field visits to sites managed for R. ponticum in the past .............................. 19 7.1 Site selection ..................................................................................................................19 7.2 Rhododendron survey – methods and results.................................................................20 8 Element 6: Site management decision tool ..................................................................... 21 9 Element 7: Set up monitoring at selected sites ............................................................... 29 10 Element 8: Recommendations for future research and management ............................. 36 11 References ...................................................................................................................... 47 12 Acknowledgments ........................................................................................................... 50 13 Proposal for year 2 development of project..................................................................... 50 Appendices Field record form for priority sites – bryophytes Field record form for priority sites – lichens Plantlife invasive species field recording sheet – rhododendron Some interesting and notable lichen species recorded during the Plantlife Scotland survey 2007 by Andy Acton and Anna Griffith Project data (files on separate data disk, available on request from Plantlife Scotland) Threatened woodland desk study - Collated data.xls 2/7/07 (Excel) Rhododendron management audit – Data input form.xls 31/5/07 (Excel) Rhododendron management audit – Collated data.xls 6/7/07 (Excel) Abbreviated Summary of West Highland Rhododendron Schemes.xls 6/7/07 (Excel) Collated bryophyte field records.xls 6/7/07 (Excel) Site species lists - Bryophytes (EK).xls 3/7/07 (Excel) Site species lists - Bryophytes (GPR) – Microsoft Word 12/6/07 Bryophyte monitoring plots on rhododendron-cleared sites – Microsoft Word 16/6/07 Collated lichen field records.xls 6/7/07 (Excel) Site species lists – Lichens.xls 8/6/07 (Excel) Map showing distribution of lichen and bryophyte priority sites visited (JPEG image) Map showing priority site visits with rhododendron absent (JPEG image) Map showing priority site visits with rhododendron present (JPEG image) Map showing priority sites identified in project (vists and desk research) (JPEG image) Map showing sites included in rhododendron audit (JPEG image) I 1 GEOGRAPHIC AND ECOLOGICAL SCOPE The geographic scope of this project corresponds to the tentative West coast Important Plant Area (Plantlife in press) (Figure 1). This area has been proposed as an Important Plant Area owing to its Atlantic woodlands and qualifying on the following criteria: A. Site holds significant population of one or more species of global or European conservation concern. These include Herbertus borealis, Lejeunea mandonii, Radula carringtonii, Daltonia splachnoides, Jamesoniella undulifolia plus eight species of Euphrasia. B. Site has an exceptionally rich flora in a European context in relation to its biogeographic zone. The proposed IPA includes the rich cryptogamic flora of Atlantic woodland on the west coast of Scotland, which is rare elsewhere across the globe. C. Site is an outstanding example of a habitat type of global or European plant conservation and botanical importance. This includes the EC Habitat Directive Annex 1 habitat “old sessile oakwoods with Ilex and Blechnum in the British Isles”, which is widely represented in the proposed IPA. 1 Figure 1: Tentative West coast Important Plant Area (Plantlife in press) Derived from MiniScale by Ordnance Survey. Reproduced from Ordnance Survey digital map data. © Crown Copyright 2003. All rights reserved. 2 Atlantic woodland is defined by its distinctively rich cryptogamic flora and its limited distribution across the world. These wet oak and hazel woodlands are characterised by the thick mossy carpets that cover rocks and tree bases, while the trees themselves are festooned in layers of mosses and lichens. This habitat has been described as the Celtic rainforest (Gilbert 2004). Many of these species, although locally abundant in western Scotland, are limited elsewhere in the world to the extreme western seaboard of Europe and the Atlantic islands including the Azores and Madeira. These species that are rare in European terms, are those for which Scotland has special responsibility. The rich cryptogamic species diversity of Atlantic woodland is based on a number of environmental variables (Baarda 2005): • Wetness / temperate rainforest • Western / oceanic / Atlantic climate • Upland / steep / poor soils • Presence of characteristic bryophytes and lower plants, eg Adelanthus decipiens, Radula aquilegia, Plagiochila spinulosa • Quality / rarity / uniqueness • Need for management • Oak and / or hazel Vegetation characteristics Vegetation types that make up Atlantic woodland include W17 (Quercus petraea-Betula pubescens-Dicranum majus woodland), W11 (Quercus petraea – Betula pubescens – Oxalis acetosella woodland) (Rodwell 1991) and hazel woodland, with pockets of W7 (Alnus glutinosa – Fraxinus excelsior – Lysimachia nemorum woodland) and W9 (Fraxinus excelsior – Sorbus aucuparia – Mercurialis perennis woodland) (Rodwell 1991). In descriptions of W17, Rodwell et al. (2002) describe Rhododendron ponticum as a vigorous invader. As such it “poses a serious threat to the rich oceanic bryophyte and lichen floras in many W17 woods in north Wales, the Lake District, the western Highlands and western Ireland. Clearance of rhododendron has taken place in many western woods; methods vary from manual cutting and subsequent treatment of stumps to clearance using a mechanical flail. Observations suggest that following clearance, recovery of the woodland vegetation is a very slow process, and that some of the rarer bryophytes and lichens might never return.” See recommendations on control. Both W11 and W17 occur in the EC Habitat Directive Annex 1 habitat “old sessile oakwoods with Ilex and Blechnum in the British Isles”. Special Area of Conservation status (SAC) has been designated to approximately 19% of the total UK old sessile oak habitat, many of which occur along Scotland’s west coast (Figures 2 and 3). The remaining 81% of the UK old sessile oak habitat is of insufficient quality in terms of habitat structure and function to meet SAC standards (JNCC 2003). 3 Figure 2: Distribution of old sessile oak woods across Britain (www.jncc.gov.uk) Figure 3: Distribution of old sessile oak wood SACs in Britain (www.jncc.gov.uk) 4 Lichens For lichens, four characteristic communities of species are found in Scotland’s Atlantic woodlands: • Graphidion scriptae • Parmelion laevigatae • Lobarion pulmonariae • Usneion barbatae The numbers of lichen species typically found in an Atlantic woodland are mainly in the range of 100 – 200 (Coppins and Coppins 2005). Characteristic species include Graphis alboscripta, which has not been found outside Scotland to date and Lobaria pulmonaria. Lobaria pulmonaria, listed on Red Lists in other European countries, is locally abundant in Scotland, where its largest populations remain. However, it has suffered a significant decline in European lowlands during the last decades and therefore is considered as endangered throughout Europe. (Zoller et al. 1999). The biggest threat to the lichens of the oak and hazel woodlands of Scotland’s west coast is the invasion of Rhododendron ponticum (Coppins and Coppins 2005). Bryophytes The oceanic bryophyte element of British and Irish Atlantic woodlands is the richest bryophyte flora in Europe and one of the richest in the world, rivalling the bryophyte flora of tropical montane cloud forests (Porley and Hodgetts 2005). Most good Atlantic woodlands will contain more than 200 different species of moss and liverwort (Rothero 2005). Indicator species