CENTRE FOR ECOLOGY AND HYDROLOGY NATURAL ENVIRONMENT RESEARCH COUNCIL The Changing Distribution of the Flora of the United Kingdom: Technical Report C. D. Preston, M. G. Telfer, D.B. Roy, P. D. Carey, M. O. Hill, W. R. Meek, P. Rothery, S.M. Smart, G.M. Smith, K. J. Walker (CEH) D A Pearman (BSBI) July 2003 CEH PROJECT No: C01093 Centre for Ecology and Hydrology CEH Monks Wood Abbots Ripton, Huntingdon, Cambs. UK CONTENTS EXECUTIVE SUMMARY .........................................................................................1 INTRODUCTION........................................................................................................3 MODULE 1 – CHARACTERISING HABITAT REQUIREMENTS OF SPECIES ......................................................................................................................5 1.1 Frequency of occurrence of plant species in Broad Habitat categories.........................................5 1.2 Calculation of species’ preference indices to Broad Habitat categories....................................... 5 1.3 Validation and extension of characteristic species lists .................................................................6 MODULE 2 - MODELS OF EXPECTED SPECIES DIVERSITY........................7 2.1 Definition of local species pool ......................................................................................................7 2.2 Categorization of taxa by likely completeness of recording...........................................................7 2.3 Attributes of 10-km squares............................................................................................................7 2.4 Basic analysis of well-recorded native species in squares with >30% land ..................................8 2.5 Basic analysis for native species .................................................................................................10 2.6 Variation in coverage attributable to difficult species..................................................................12 2.7 Variation in coverage attributable to neophytes ..........................................................................13 2.8 Coastal, aquatic and urban species..............................................................................................13 2.9 Estimating coverage in boundary squares....................................................................................13 2.10 Estimating coverage in squares with little land..........................................................................14 2.11 Synthesis of coverage by date class and vice-county..................................................................14 MODULE 3 - ANALYSING CHANGE IN THE UK AND ITS COMPONENT COUNTRIES AND REGIONS.................................................................................17 3.1 Introduction ..................................................................................................................................17 3.2 Analysis of change in Britain in relation to habitat (Stage 1) ......................................................17 3.3 Analysis of change in countries and regions (Stage 2).................................................................23 3.4 Quantitative analysis of the dynamism of species (Stage 3) .........................................................36 3.5 Analysis of change in relation to frequency and conservation status (Stage 4) ...........................41 3.6 Spatial analysis of change (Stage 5).............................................................................................47 MODULE 4 - COMPARISON WITH OTHER STUDIES....................................49 4.1 Comparison with the results of the countryside survey ................................................................49 4.2 Comparison with results in county Floras....................................................................................55 ACKNOWLEDGEMENTS ......................................................................................59 REFERENCES...........................................................................................................59 ANNEX 1 Notes on the definitions of broad habitats ANNEX 2 Broad habitat associations of native and archaeophyte species ANNEX 3 Maps of broad habitat types ANNEX 4 Regional change index values ANNEX 5 Extinction proportion, colonisation proportion, dynamism index and dynamism score ANNEX 6 Species reported by the New Atlas and the Countryside Survey ANNEX 7 Comparison of trends revealed by New Atlas and Countryside Survey datasets ANNEX 8 Suggested reasons for differences between results obtained by New Atlas and Countryside Survey analyses EXECUTIVE SUMMARY This Report presents the results of analyses of data collected for the New Atlas of the British and Irish Flora, a survey of the distribution of vascular plant species in Britain and Ireland carried out between 1987 and 1999. It includes comparisons with the only previous such survey, published in 1962 in the Atlas of the British Flora. The analyses are carried out for the U.K., on a regional basis and at a 10-km square scale. Analyses of floristic change have hitherto been handicapped by the absence of a classification of species into habitat categories. We have therefore allocated native and archaeophyte species to the Broad Habitat (BH) categories devised for the UK Biodiversity Action Plan. To do this, we calculated preference indices using the quadrat data collected for the National Vegetation Classification and for the Countryside Survey 2000 project. Additional information, including the species accounts published in the New Atlas, were used to extend the classification to the rarer species which are not adequately covered in the quadrat databases. The next section of the report analyses the geographical variation in the number of species recorded per 10-km square. The total of non-critical native and archaeophyte species expected in a 10-km square has been modelled using combinations of geological, climatic, topographic and habitat variables. In the UK, 65% of the variation found in the species richness of these squares can be attributed to climatic factors. Including the full range of variables improved the model fit to 76%. Models that adjusted for the richness of the local species pool (biogeographic zones) were generally little better than those obtained using a single species pool for the whole of the UK. Separate models of species richness developed for each Broad Habitat, varied in their prediction success from 34% to 88%. Linear and boundary features, Built-up areas and Montane habitats were best predicted. The worst-predicted Broad Habitats were Acid grassland, Inland rock, and Fen marsh and swamp. Models have also been applied to provide an expected estimate of those native species which are difficult to record, and to neophytes. The variation in recording intensity in the three recording periods mapped in the New Atlas (pre-1970, 1970-1986, 1987 onwards) is summarised in a series of vice-county maps which shows that most counties were at least moderately well recorded in the pre-1970 and post-1986 periods. The exceptions are identified. The relative success of vascular plants characteristic of different Broad Habitat categories is analysed using a change index developed in an earlier paper. In Britain as a whole, native and archaeophyte species in the Arable and horticultural, Dwarf shrub heath, Calcareous grassland, Bog, Montane and Acid grassland categories have been the least successful, whereas those of Improved grassland and Built-up areas and gardens have done relatively well. When the results are analysed for individual countries and regions of the UK there is considerable geographical variation: species of Arable and horticultural habitats have done less well in the three regions of Scotland examined than elsewhere, for example, whereas those of Acidic grassland show little change in the Scottish regions but a marked decrease elsewhere. Changes in plants of aquatic habitats (Rivers and streams, Standing water and canals) are difficult to interpret because as a group they were under-recorded in 1930-69 but covered by intensive, targeted recording in Scotland and N. Ireland in the later period. 1 There is also marked geographical variation in the patterns of change analysed for species with different ecological attributes. • The relative success of neophytes, decline of archaeophytes and stability of native species is shown in almost all regions, but in Scotland archaeophytes have declined to an even greater extent than elsewhere, and neophytes have been less successful. • Species characteristic of habitats with high nutrient levels have been relatively successful in almost all areas except the Scottish Highlands, but in England the success of these species has been particularly marked. • Species characteristic of sites with very acidic or very basic soils have been less successful than those of circum-neutral conditions in all areas except the Scottish Highlands. • In many areas species of shaded conditions have been more successful than those of unshaded sites, but there is no significant trend in S.E. England, N. and N.W. England and Highland Scotland, and the trend is in the opposite direction in S.W. Scotland. • Tall plants (which tend to be more competitive) have been more successful than short plants in all areas except Highland Scotland. • Northern species have declined in all regions except Highland Scotland. A ‘dynamism index’