MIRE in BROADLAND, NORFOLK. By
Total Page：16
File Type：pdf, Size：1020Kb
ASPECTS OF THE PLANT ECOLOGY OF A FLOOD-PLAIN MIRE IN BROADLAND, NORFOLK. By KENNETHE. GILLER Department of Botany, University of Sheffield Thesis for the degree of Doctor in Philosophy FEBRUARY1982 TO MY PARENTS AND ANA ASPECTS OF THE PLANT ECOLOGY OF A FLOOD-PLAIN MIRE IN BROADLAND, NORFOLK. KENNETH E. GILLER Department of Botany, University of Sheffield SUMMARY The vegetation of a particularly diverse area of undrained flood-plain mire is described. Factors and processes important in determining the distribution of community-types within the study area have been investigated. Investigation of the alluvial stratigraphy has revealed the presence of a complex pattern of peat cuttings. Succcession within the peat cuttings, with appropriate vegetation management, has led to the formation of CZadium mariscus-, Phragmites communis- and Juncus subnoduZosus-dominated fen vegetation and, in some areas, poor-fen communities with much Sphagnum. In areas not cut for peat, iiianagement his also sustained -,arious rich-f en herbaceous communities (different to those of the cuttings); in its absence, fen carr develops. The differences in successional development in peat cutting areas and those not cut for peat is mainly due to difference in hydrological status. Long term experiments established to examine effects of different management techniques are described. Studies of peat and peat water chemistry in a representative selection of community-types has demonstrated local areas of high salinity, caused by incursions of brackish water due to exceptionally high tides and, particularly, the influence of underlying estuarine deposits. Although large areas are flooded by river water there is little evidence for eutrophication, except very locally. Indeed, 'seral oligotrophication' is occurring in isolated areas. This may preceed, but is not a pre-requisite for, Sphagnum invasion. The most species-rich communities are developed in non-saline areas with a fairly stable water level; they may, however, be dependent upon flooding by river water for maintenance of their base status. Possible directions of future succession are discussed. ---_: _ ý.ý ý ýý t'i'=_ý. __.. .-_--_ ý_ .... ý .-ý. ý =, "rý, PLATE 1. A small turf-pond (Ferside Inner Broad) July 1978 ý* A fiý r :. A; c _.rký. w IAL 1u l' `i L6 PLATE 2. The central part of Great Fen during sedge mowing July 1977. ACKNOWLEDGEMENTS I like would to thank all of the people who have helped me with this project. I am particularly grateful to. Professor A. J. Willis for allowing the use of departmental facilities; Dr B. D. Wheeler for introducing me to the fens of Broadland, for supervising the research and for help in the field; Mr D. S. A. McDougall and Mr P. Neave for free access to the study area and allocation of plots for management experiments; Miss R. E. D. Cooke for all her able assistance; Mrs D. M. Freeman especially for preparing all of the figures; Miss E. Gibson for endless patience in typing the manuscript; Mr P. A. Wright of the N. C. C., Norwich; Mr P. W. Lambley of the Castle Museum, Norwich; Dr and Mrs E. A. Ellis for helpful discussion and hospitality; the late Mr J. V. Gane and his wife for their friendship, discussion and rowing boat; the staff at How Hill Education Centre for camping facilities; the staff and locals of Sutton Staithe Hotel for friendship; Dr J. D. Biggins for statistical advice; the Nature Conservancy Council for providing the funds and to all who have made the Botany Department at Sheffield such a pleasurable place of work. CONTENTS Page CHAPTER 1 INTRODUCTION 1.1. PERSPECTIVE 1 1.2. BROADLAND 2 1.3. RATIONALE 3 1.3.1. Broadland Research 3 1.3.2. Factors and Processes in mire Ecology 4 1.4. THE STUDY AREA 5 1.5. RESEARCHAPPROACH 8 CHAPTER 2 THE PRESENT VEGETATION 2.1. INTRODUCTION 10 2.2 METHODS 11 2.3. ADDITIONAL VEGETATION CATEGORIES 13 2.4. SWAMP AND FEN VEGETATION 14 2.4.1. Swamp vegetation 14 2.4.2. Herbaceous fen vegetation 15 2.4.3 Fen woodland vegetation 25 2.4.4. Marginal vegetation 29 2.5. VEGETATION OF THE DYKES AND POOLS 32 2.6. DISCUSSION 35 CHAPTER 3 ALLUVIAL STRATIGRAPHYAND VEGETATION SUCCESSION 3.1. INTRODUCTION 37 3.2. METHODS 37 3.3. THE PEAT STRATIGRAPHYDIAGRAMS 39 3.3.1. Sedge Marshes-Fenside Marsh Section 39 3.3.2. Great Fen Section 42 3.3.3. Great Fen-Barton Broad Section 46 3.3.4. Fenside-Irstead Holmes Section 48 3.3.5. Additional Peat Borings 51 Page 3.4. AN INTERPRETATION OF THE PEAT STRATIGRAPHY 52 3.4.1. Brushwood peat, clays and peat cuttings 53 3.4.2. The depth and timing of the peat cuttings 56 3.5. INFERRED SUCCESSIONAL CHANGES IN THE PAST VEGETATION 60 3.5.1. Succession in the peat cuttings 60 3.5.2. Succession in areas not cut for peat 61 3.5.3. Discussion 62 3.6. CONCLUSIONS 64 CHAPTER 4 INVESTIGATIONS OF ENVIRONMENTAL PARAMETERS IN SELECTED STUDY SITES 4.1. INTRODUCTION 66 4.2. THE RATIONALE FOR SAMPLE COLLECTION AND THE STUDY SITES 67 4.2.1. Rationale for peat and water sampling 67 4.2.2. Selection of study sites 69 4.3. MATERIALS AND METHODS 70 4.3.1. Water sampling 70 4.3.2. Water level measurement 72 4.3.3. Peat sampling 73 4.3.4. Methods for chemical analysis and data processing 73 4.4. HYDROLOGICAL INVESTIGATIONS 4.4.1. Local precipitation and water levels in the dyke systems 74 4.4.2. Water level relative to the peat surface 76 4.4.3. Vertical movement of the peat surface 82 4.4.4. Water movement 84 4.4.5. The relationship between the hydrology and vegetation of the study sites 87 4.4.6. Conclusions 94 Page 4.5. INVESTIGATIONS OF THE CHEMISTRY OF THE PEATS AND PEAT WATERS 97 4.5.1. pH 98 4.5.2. Dry weight per unit volume 100 4.5.3. Ash content 102 4.5.4. Nitrogen 103 4.5.5. Phosphorus 110 4.5.6. Iron and Manganese 112 4.5.7. Major cations 118 4.5.8. Major anions in peat waters 131 4.5.9. Electrical conductivity of the peat waters (Kcorr) 133 4.5.10. Redox potential 134 4.5.11. Sulphide 135 4.5.12. Fluctuations in the chemical composition of the peat waters between September 1979 and September 1980 138 4.5.13. Cluster analysis 144 4.5.14. Discussion 147 4.5.15. Conclusions 155 CHATPER 5 FURTHER INVESTIGATIONS OF THE RELATIONSHIP BETWEEN THE VEGETATION AND THE CHEMISTRY OF THE PEATS AND PEAT WATERS 5.1. INTRODUCTION 159 5.2. METHODS 159 5.3. THE INFLUENCE OF FLOODING BY RIVER WATER ON THE CHEMISTRY OF THE FENS 160 5.3.1. Analysis of nitrogen and phosphorus in surface waters 160 5.3.2. Analysis of chemical variables along a transect from Barton Broad to Great Fen 162 5.4. CATION LEVELS IN THE DYKES AND FENS 164 5.4.1. Levels of cations in waters from the dykes 164 5.4.2. The sources of the major cations in relation to the fens 165 5.5. FURTHER STUDIES IN SELECTED COMMUNITIES 168 5.5.1. Investigations in Great Fen 168 5.5.2. Investigations in Little Fen and Neatishead Poor's Fen 171 5.5.3. Investigations in Irstead Poor's Fen 172 Page 5.5.4. Investigations in Sedge Marshes 175 5.5.5. Investigations in Fenside Marsh 176 5.5.6. Investigations in Main Reed Marsh 177 5.6. DISCUSSION 180 5.6.1. The chemistry of the surface peats and peat waters in relation to possible water sources 180 5.6.2. Chemical stratification of the peat waters 182 5.6.3. Surface oligotrophication of the fens 188 5.7. CONCLUSIONS 190 CHAPTER 6 THE EFFECTS OF MANAGEMENT ON THE VEGETATION OF THE STUDY AREA 6.1. INTRODUCTION 192 6.2. MATERIALS AND METHODS 193 6.2.1. Experimental design 193 6.2.2. Management 193 6.2.3. Monitoring of management experiments 194 6.2.4. Measurements of light attenuation 194 6.2.5. Problems of vegetation recording in herbaceous fen vegetation 195 6.3. ANECDOTAL, OBSERVATIONAL AND CARTOLOGICAL EVIDENCE OF MANAGEMENT 196 6.4. MANAGEMENT EXPERIMENTS 200 6.4.1. Neatishead Poor's Fen Experiment 200 6.4.2. Little Fen experiment 202 6.4.3. Great Fen (North) experiment 204 6.4.4. Fenside Marsh experiment 206 6.4.5. Main Reed Marsh experiment 208 6.5. MEASUREMENTS OF LIGHT ATTENUATION IN HERBACEOUS FEN VEGETATION 209 6.6. DISCUSSION 211 6.6.1. Management, light attenuation and possible effects on the vegetation 211 6.6.2. Management and oligotrophication 215 6.6.3. Other management practices 216 6.6.4. The invasion of carr 217 6.7. CONCLUSIONS 218 Page CHAPTER 7 GENERAL DISCUSSION 7.1. GRADIENTS OF CHEMICAL VARIATION 220 7.2. GENERAL RELATIONSHIPS TO ENVIRONMENTAL GRADIENTS 222 7.2.1. Chemical gradients 222 7.2.2. Hydrological gradients 224 7.2.3. Vegetation development in relation to past environmental gradients 226 7.3. SOME VEGETATION-TYPES OF PARTICULAR INTEREST 229 7.3.1. Species-rich sedge beds 229 7.3.2. Reed beds 231 7.3.3. The development of poor-fen communities 2 32 7.4. FUTURE SUCCESSION AND MANAGEMENT FOR THE CONSERVATIONOF COMMUNITIES 2 34 7.4.1. The fate of herbaceous plant communities 234 7.4.2. Possible climax vegetation 237 BIBLIOGRAPHY APPENDIX 1 Locations of species-lists in Tables 2.2 and 2.3.