Vegetation communities of British lakes: a revised classification Vegetation communities of British lakes: a revised classification Catherine Duigan, Countryside Council for Wales, Penrhos Road, Bangor, Gwynedd, LL57 2DW Warren Kovach, Kovach Computing Services, 85 Nant Y Felin, Pentraeth, Anglesey, LL75 8UY Margaret Palmer, Nethercott, Stamford Road, Barnack, Stamford, PE9 3EZ Joint Nature Conservation Committee, Monkstone House, City Road, Peterborough, PE1 1JY © JNCC 2006 ISBN-13 978 1 86107 575 8 ISBN-10 1 86107 575 8 1 2 Contents List of tables and figures 5 Summary 6 Chapter 1 Introduction 7 Chapter 2 Survey method 9 Chapter 3 The dataset, data analysis and the Plant Lake Ecotype Index (PLEX) 10 The dataset 10 Data analysis 10 Plant Lake Ecotype Index 12 Chapter 4 Revised classification system and lake key 14 Chapter 5 Individual descriptions of the lake groups 21 Group A Small, predominantly northern dystrophic peat or heathland pools, dominated by Sphagnum spp. 23 Group B Widespread, usually low-lying acid moorland or heathland pools and small lakes, with a limited range of plants, especially Juncus bulbosus, Potamogeton polygonifolius and Sphagnum spp. 24 Group C1 Northern, usually small to medium-sized, acid, largely mountain lakes, with a limited range of plants, but Juncus bulbosus and Sparganium angustifolium constant 25 Group C2 North western, predominantly large, slightly acid, upland lakes, supporting a diversity of plant species, Juncus bulbosus constant, often with Littorella uniflora and Lobelia dortmanna, in association with Myriophyllum alterniflorum 26 Group D Widespread, often large, mid-altitude circumneutral lakes, with a high diversity of plants, including Littorella uniflora, Myriophyllum alterniflorum, Callitriche hamulata, Fontinalis antipyretica and Glyceria fluitans 28 Group E Northern, often large, low altitude and coastal, above-neutral lakes with high diversity of plant species, including Littorella uniflora, Myriophyllum alterniflorum, Potamogeton perfoliatus and Chara spp. 30 Group F Widespread, usually medium-sized, lowland, above neutral lakes, with a limited range of species, but typified by water-lilies and other floating-leaved vegetation 32 Group G Central and eastern, above neutral, lowland lakes, with Lemna minor, Elodea canadensis, Potamogeton natans and Persicaria amphibia 33 Group H Northern, small, circumneutral, lowland lakes, with low species diversity characterised by the presence of Glyceria fluitans and Callitriche stagnalis 35 Group I Widespread, mostly moderately large, base-rich lowland lakes, with Chara spp., Myriophyllum spicatum and a diversity of Potamogeton species 36 Group J Northern coastal, brackish lakes, with Potamogeton pectinatus, Enteromorpha spp., Ruppia maritima and fucoid algae 38 3 Vegetation communities of British Lakes Contents Chapter 6 Using the Plant Lake Ecotype Index (PLEX) 45 Case Study One: Llangorse Lake, Wales (Lake Group I) 45 Case Study Two: Loch Chon, Scotland (Lake Group C2) 47 Conclusions 48 Chapter 7 Discussion 49 The lake resource 49 Analysis and classification schemes 50 Regional studies 52 Future developments 53 Chapter 8 Acknowledgements 55 Chapter 9 References 56 Chapter 10 Annexes 58 Annex A A listing of submerged and floating macrophyte taxa included in the 1989 TWINSPAN analysis (Palmer et al. 1992) and the 2004 re-analysis of the JNCC lake dataset described in this report, with the number of records used 58 Annex B Constancy table for standing water site types: submerged and floating plants with number of occurrences and PLEX values 61 Annex C Relationships between the environmental variables, taxon richness and PLEX 64 Annex D Sites included in this study 70 4 List of figures and tables List of figures and tables Page Figure 3.1. Distribution of lakes included in the analysis 10 Figure 3.2. Dendrogram of TWINSPAN analysis showing major groups A-J 11 Figure 3.3. Ranges of PLEX scores for lake groups 13 Figure 3.4. PLEX scores plotted against pH 13 Figure 3.5. PLEX scores plotted against alkalinity 13 Figure 4.1. Ranges of altitude for lake groups 17 Figure 4.2. Ranges of surface area for lake groups 17 Figure 4.3. Ranges of pH for lake groups 17 Figure 4.4. Ranges of conductivity for lake groups 17 Figure 4.5. Ranges of alkalinity for lake groups 18 Figure 4.6. Ranges of taxon richness for lake groups 18 Figure 4.7. Number of sites per lake group for Scotland, England and Wales 18 Figure 4.8. Ordination diagram of a CCA analysis, including the major environmental variables 19 Figure 6.1. PLEX scores through time for Llangorse Lake 46 Figure 6.2. PLEX scores through time for Loch Chon 47 Figure 7.1. Distribution of standing waters in Britain 49 Figure 7.2. Pie chart showing percentage distribution of lakes surveyed within groups 50 Figure 7.3. An illustration of the relationship between the lake groups described in this report and those protected under the Habitats Directive 51 Table 4.1. Constancy table for site groups 15 Table 4.2. Key to standing water site types using submerged and floating taxa 16 Table 4.3. Statistics for the CCA analysis in Figure 4.8 19 Table 4.4. Statistics for the CCA analysis incorporating 100km grid squares 20 Table 5.1. Rarity status of submerged and floating standing water plants 21 Table 6.1. Calculating a time series of mean site PLEX scores for Llangorse Lake. 46 Table 6.2. Calculating a time series of mean site PLEX scores for Loch Chon. 47 Table 7.1. The relationship between Lake Groups in the new classification and Site Types in the previous classification: numbers of sites within each class. 51 5 Vegetation communities of British Lakes Summary The first comprehensive classification scheme for This report presents the results of the statistical standing waters in Britain (Palmer 1992; Palmer et al. analysis of the enlarged dataset. Differences from the 1992) was based on macrophyte surveys carried out by previous classification are highlighted. The important the Nature Conservancy Council (NCC) from 1124 components of this report include: standing waters throughout England, Scotland and Wales between 1975 and 1988. This dataset became an u separate ecological descriptions of 11 distinct lake important source of information used for a variety of groups (A-J); purposes including conservation site selection and the identification of aquatic communities in the National u a revised key for the classification of newly surveyed Vegetation Classification (NVC) (Rodwell et al. 1995). sites; The macrophyte records were also used in a number of u atlases (Preston & Croft 1997; Preston et al. 2002). updated distribution maps showing the distribution of sites within each lake group, supported by summary environmental data and macrophyte Since then, the NCC and its successor organisations constancy tables; (Countryside Council for Wales (CCW), English Nature (EN) and Scottish Natural Heritage (SNH)) have u the earlier Trophic Ranking Scheme (TRS) is replaced commissioned a substantial number of additional lake by a Plant Lake Ecotype Index (PLEX), which reflects surveys, leading to the establishment of a much larger the fit with the new classification scheme rather than dataset with records from 3447 sites (310 England, 38 a perceived simple trophic relationship. Wales and 3099 Scotland). The advent of the Habitats Directive (Council Directive 92/43/EEC on the conservation of natural habitats and of wild fauna and flora) and more recently the Water Framework Directive (Directive of the European Parliament and of the Council establishing a framework for Community action in the field of water policy) provided the incentive for the production of a revised classification using this larger dataset, supplemented by environmental data. 6 Chapter 1 Introduction Chapter 1: Introduction Aquatic plants are important ecological components focused on the areas with the highest concentrations of of lakes, where they have a complex role in the structure lakes and where management information was required. and functioning of the ecosystem (Moss^ 1998; Scheffer A comprehensive dataset has also been established for 1998; Wetzel 2001; Pokorny’ & Kvet 2004). The statutory lakes in Northern Ireland (Wolfe-Murphy et al. 1992) but conservation agencies in England, Wales and Scotland it was not included in this analysis. have a long history of carrying out routine macrophyte surveys of standing waters, which has led to the In 1992 the European Community adopted Council accumulation of a large dataset held by the Joint Nature Directive 92/43/EEC on the conservation of natural habitats Conservation Committee (JNCC). The primary aim of and of wild fauna and flora, commonly known as the this survey effort was to describe the botanical resource Habitats Directive. The main aim of this Directive is “to of standing waters in Britain. Rare species and plant contribute towards ensuring biodiversity through the assemblages representative of lake types have been conservation of natural habitats and of wild fauna and selected as features for protection on Sites of Special flora in the European territory of the Member States to Scientific Interest (SSSIs) throughout this region. The which the Treaty applies”. It also brought an obligation process of conservation site selection requires the ability for each member state to select, designate and protect a to compare sites and set them in a local and national series of sites, to be called Special Areas of Conservation context (Nature Conservancy Council 1989). For this (SACs). In Britain,