Durham E-Theses A comparison between primary grasslands and abandoned quarries of the magnesian limestone, county Durham, with special reference to scrub invasion Allchin, Elizabeth How to cite: Allchin, Elizabeth (1993) A comparison between primary grasslands and abandoned quarries of the magnesian limestone, county Durham, with special reference to scrub invasion, Durham theses, Durham University. Available at Durham E-Theses Online: http://etheses.dur.ac.uk/5686/ Use policy The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in Durham E-Theses • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full Durham E-Theses policy for further details. Academic Support Oce, Durham University, University Oce, Old Elvet, Durham DH1 3HP e-mail: [email protected] Tel: +44 0191 334 6107 http://etheses.dur.ac.uk 2 A ·COMPARISON BETWEEN PRIMARY GRASSLANDS AND ABANDONED QUARRIES OF THE MAGNESIAN LIMESTONE, COUNTY DURHAM, WITH SPECIAL REFERENCE TO SCRUB INVASION by Elizabeth Allchin The copyright of this thesis rests with the author. No quotation from it should be published without his prior written consent and information derived from it should be acknowledged. A dissertation submitted in part fulfillment of the requirements for the degree of Master of Science in Ecology by advanced course. University of Durham 1993 ~ 8 MAR 1994 Epipactis atrorubens Acknowledgements I am very grateful to my supervisor, Dr. Brian Huntley for all his help and patience throughout the project. Dr. Tusi Butterfield provided help when it was in desperate need during data analysis. I must also thank Dr. Val Standen for her suggestions and criticism, and for driving me to Witton-le-Wear. Julie Stobbs at Durham County Council and Trina and John Barrett at English Nature provided information on management of the SSSis. I am also grateful to Jenny for having 'done it before' and helping with identification and to Sean for keeping me sane in the last week of writing up! Abstract Seven grassland Sites of Special Scientific Interest on the Magnesian Limestone of County Durham were botanically surveyed using the methodology of the National Vegetation Classification. Both primary grasslands and grassland developed in abandoned quarries were included, but the sampling was limited to open calcicolous grassland and scrub-invaded grassland, with areas of impenetrable scrub and woodland being avoided. Characteristic of these grasslands is blue moor grass, Ses/eria a/bicans, which reaches its southern lowland limit in County Durham. The results were analysed using multivariate techniques to reveal patterns in community composition and possible environmental factors causing this variation. Six main communities are described, comprising both grassland and scrub vegetation. A successional sequence linking these communities and their sub-communities is postulated. It is suggested that abandoned quarries are floristically different from primary grasslands, but may achieve similarity in time if there is a nearby seed source of S. a/bicans. Scrub invasion, mainly by hawthorn, Crataegus monogyna, is ubiquitous in both the primary and secondary grasslands and presents the major threat to the integrity of the limestone flora. The botanical survey reveals a significant change to the flora under scrub, with some of the low-growing calcicoles being partially replaced by tall nutrient-demanding grasses and herbaceous species. However, the invasion of willow (Salix spp.) at one of the abandoned quarries has had negligible impact on the ground flora. The two most common scrub species, hawthorn and dog rose (Rosa canina agg.) appear to have more influence on the ground flora than any other species. It is suggested that the age of these species is more important than density in altering the ground flora. The results of this investigation have been used to make tentative suggestions for management of the sites. Contents Chapter One- Introduction 1 1.1 Magnesian Limestone grasslands 1 1.2 Geology 3 1.3 Geomorphology 4 1.4 Soils 5 1.5 Climate 6 1.6 Quarrying 6 1.7 Vegetation history 7 1.8 Aims of this investigation 9 Chapter Two - Site descriptions 2.1 Trimdon 10 2.2 Bishop Middleham 11 2.3 Raisby Hill Grassland 14 2.4 Wingate 14 2.5 Pittington Hill 15 2.6 Thrislington Plantation 19 2.7 Cassop Vale 25 Chapter Three - Materials and methods 3.1 Sampling 27 3.2 Environmental measurements 28 3.3 Multivariate analysis 28 Chapter Four- Results 4.1 Classification of communities 30 4.2 Ordination 45 4.3 Canonical Correspondence Analysis 52 4.4 Specific effects of scrub invasion on soil pH and calcicolous species Chapter Five- Discussion 5.1 Succession 71 5.2 The impact of scrub on limestone 79 grassland vegetation 5.3 Effects of different scrub species 82 5.4 Differences between primary and 82 secondary grasslands 5.5 Suggestions for management 83 References 85 List of Tables 1.1 Some species at the edge of their range in County 2 Durham 1.2 Uses of Magnesian Limestone 7 3.1 Domin Scale of abundance 27 4.1 Summary of communities and sub-communities 32 4.2 Summary of Ses/eria a/bicans grassland community 33 and sub-communities 4.3 Summary of Crataegus monogyna scrub community 40 and sub-communities 4.4 Eigenvalues of the first 4 principal axes of variation in 45 the floristic data 4.5 Eigenvalues of DCA, CCA and 3 partial CCAs 52 4.6 Partial correlation coefficients, canonical coefficients 55 and t-values in PCCA 2 4.7 Partial correlation coefficients, canonical coefficients 62 and t-values in PCCA 3 4.8 The occurrence of seven calcicoles under scrub 69 5.1 Analysis of soils from Thrislington 80 List of Figures 1.1 Distribution map of Ses/eria a/bicans 1 1.2 Geological map of eastern County Durham 3 1.3 Distribution of soil types on the Magnesian Limestone 5 4.1 Species ordination 48 4.2 Samples ordination (codes) 49 4.3 Samples ordination 50 4.4 Selected species ordination 51 4.5 PCCA 2: Species 56 4.6 PCCA 2: Selected species 58 4.7 PCCA 2: Samples (codes) 59 4.8 PCCA 2: Samples 60 4.9 PCCA 3: Species 64 4.10 PCCA 3: Selected species 65 4.11 PCCA 3: Samples (codes) 66 List of Photographs Frontispiece Epipactis atrorubens 1 Sparsely colonised spoil heap at Bishop Middleham 12 2 Ses/eria a/bicans grassland at the rim of Bishop 12 Middleham Quarry (foreground) with Salix scrub colonising the quarry floor 3 Bee orchid (Ophrys apifera) at Bishop M iddleham 13 4 Scrub encroachment on Raisby Hill Grassland 16 5 Raisby Quarry Floor 16 6 Scrub encroachment at Wingate 17 7 Scrub encroachment at Wingate 17 8 Bramble (Rubus fruticosus agg.) invasion on Pittington 18 Hill 9 Pittington Quarry 18 10 Mountain Everlasting (Antennaria dioica) at 20 Thrislington 11 Perennial flax (Unum perenne ssp. anglicum) at 21 Thrislington 12 Perennial flax and rock rose (Helianthemum 21 nummularium) at Thrislington 13 Dark red helleborine (Epipactis atrorubens) at 22 Thrislington 14 Ses/eria a/bicans grassland and scrub invasion at 23 Thrislington 15 Ses/eria a/bicans grassland and scrub invasion at 23 Thrislington 16 Sheep grazing at Thrislington 24 17 Acid grassland (foreground) and calcareous grassland 26 (background) at Cassop Vale 18 Gorse ( U/ex europaeus) and Brachypodium sy/vaticum 26 at Cassop Vale 19 Pyramidal orchid (Anacamptis pyramidalis) in willow 74 scrub at Bishop Middleham 20 Common spotted orchid (Dactylorhiza fuchsi~ 75 21 Fragrant orchid (Gymnadenia conopsea) 76 22 Orchids in willow scrub at Bishop Middleham 78 List of Appendices 1 Site maps to show positions of quadrats 2 Phytosociological tables 3 Complete species list with codes 4 Description of releves 5 Species confined to primary and secondary grasslands 6 Species lists CHAPTER ONE INTRODUCTION 1.1 Magnesian Limestone Grasslands The total national resource of Magnesian Limestone grassland constitutes 270 ha, of which 177 ha are in County Durham and Tyne and Wear (English Nature, 1992). There are small pockets of grassland remaining in Derbyshire, Nottinghamshire and Yorkshire, but County Durham supports the largest remnants (Ratcliffe, 1977). These remnants comprise both 'primary' (unquarried) grasslands as well as secondary grasslands developed in abandonded quarries. Most of the original area of natural vegetation has been turned over to agriculture, so there are few areas of primary grassland remaining, most of which are on steep slopes which cannot be cultivated. These are subject to many pressures such as quarrying, agriculture, over-grazing, eutrophication, scrub invasion and recreation (Spencer, 1976). In 1975 Marren described the plight of the Magnesian Limestone as "critical, with many former sites reduced in interest, and others threatened with tipping, quarrying and scrub encroachment". In County Durham 430 ha, including woodlands, wetlands, grasslands and old quarries, retain wildlife habitat worthy of conservation. Of this, 70 ha (16%) have been destroyed since the end of the Second World War (Doody, 1977). For example, 10 of the original 24 ha in Bishop Middleham SSSI have been lost due to tipping and reworking. Scrub encroachment is perhaps the most widespread threat to the limestone flora. Pritchard (1989) suggests that approximately 60% of sites suffer from scrub invasion and that clearance of scrub could increase the amount of grassland by 15%. Not only does scrub shade out the ground flora, but the establishment of woody species can alter soil chemistry and pH (McCulloch, 1974).