Fen Management Handbook
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The Fen Management Handbook Edited by Andrew McBride, Iain Diack, Nick Droy, Bobbie Hamill, Peter Jones, Johan Schutten, Ann Skinner and Margaret Street Contents 1. Introduction and Basic Principles 7 2. Fen Flora and Fauna 14 3. Understanding Fen Hydrology 39 4. Understanding Fen Nutrients 57 5. Fen Management and Restoration 76 6. Fen Vegetation Management 101 7. Fen Water Management 144 8. Managing Fen Nutrient Enrichment 171 9. Creating Fen Habitat 186 10. Monitoring to Inform Fen Management 212 11. Fens and People 240 12. Fens From an Economic Perspective 259 Appendix I Glossary 273 Appendix II List of Acronyms Used in the Handbook 275 Appendix III Common And Scientific Names of Species Referred to in Text 276 Appendix IV NVC Classifications for Fen Habitats 287 Appendix V Legal and Regulatory Requirements for Wetland Projects 296 Appendix VI Fen Management for Bryophytes 300 Appendix VII Fen Management for Vertebrates 303 Appendix VIII Fen Managment for Invertebrates 312 Appendix IX Further Reading 322 Index 330 5 1. Introduction and Basic Principles Fens are magical places; they are an essential part of our cherished landscape. They support a rich variety of wildlife, and are often a repository of evidence of many generations of past economic use and management. With so much in their favour, it is perhaps surprising that fens are one of the least well recognised habitats, and a part of our countryside which most people understand little about. This handbook has been produced to improve understanding of fens and how they function, to explain why fens need management and to provide best practice guidance. Case studies are included at the end of most sections as practical examples of the principles and techniques outlined in the text. The handbook is aimed at anyone interested in fens, or who might become involved in fen management, creation or restoration from a practical, policy or planning perspective. Key points and good practice are highlighted in green boxes. Cautions about activities which might be legislatively controlled or which might potentially damage the interest of fens are highlighted in red boxes. Snapshot case studies in the text to illustrate specific points are highlighted in yellow. 1.1 What are fens? The word ‘fen’ is derived from the old English word ‘fenn’ meaning marsh, dirt or mud. A fen is a wetland that receives water and nutrients from surface and/or groundwater, as well as from rainfall. Differentiating between fens and bogs Fens receive most of their water via rock and soil which contain dissolved minerals creating growing conditions that allow more lush vegetation than bogs. Bogs receive water exclusively from rainfall which is acidic and contains very few minerals; consequently rain-fed acid bogs support a less diverse range of vegetation than fens. Fens are found from sea level up into the hills, across the whole of the British Isles. They range in size from tiny flushes of only a few square metres, to extensive floodplain fens covering hundreds of hectares, forming important features in the wider landscape and river catchments. 7 Map showing an indicative distribution of lowland fens in the UK (JNCC) 1.2 What’s so special about fens? Fens were prized by our ancestors for the range of products they yield: reeds and sedge for thatching, willow for basketry, hay and lush aftermath grazing for cattle. It is the past management and human interaction with fens for such purposes that has created the extremely diverse and ever-changing habitat which attracts and supports a rich variety of plants, insects, mammals and birds, and which explains why fens are described as semi-natural rather than natural habitats. Section 2: Fen Flora and Fauna explains more about the flora and fauna which make fens so special from a wildlife perspective. The UK contains a large proportion of fen types found in Europe, the surviving fragments of previously much more extensive wetlands. In his book The Illustrated History of the Countryside, Oliver Rackham suggested that “about a quarter of the British Isles is, or has been some kind of wetland.” As in other parts of Europe, the quality and extent of wetlands including fens has declined dramatically as a result of drainage, development and neglect. Some of our best agricultural soils have been provided by fens, following drainage and decades of tillage. However, the organic component of the soil that makes it so suitable for root and other crops has gradually broken down releasing carbon and lowering the land level, making the land more difficult to drain. It is estimated that of 3400 km2 of fen present in England in 1637, only 10 km2 remains today. In intensively farmed lowland areas of England, fens now occur less frequently, are smaller in size and are more isolated than in other parts of the UK. Despite these losses, the UK still boasts some large fens such as the 300 ha Insh Marshes in the floodplain of the River Spey in Scotland, the calcareous rich-fen and swamp of Broadland covering 3,000 ha in Norfolk and Suffolk, and the Lough Erne system in Northern Ireland with extensive areas of fen and swamp. In some lowland areas, such as the Scottish Borders and southern parts of Northern Ireland, there are large numbers of fens which although small (many less than 3 ha in size), are still of European importance for the rich wildlife they support. 8 Estimates of the original coverage of fen are based on the extent of deep peat soils that consist of plant remains, formed under the fen. Surviving peat deposits show how the type of fen found at a particular location can change over time. Fens can also yield valuable palaeo-ecological evidence, such as pollen, artefacts such as tools, weapons and implements, or even human bodies. Some of the best preserved pre-historic archaeological remains have been recovered from fen sites such as Flag Fen in Cambridgeshire, Star Carr in Yorkshire and the Sweet Track at Shapwick Heath in Somerset. Such finds can help reconstruct aspects of the history of fens, and our ancestors. Further information on archaeology is found in Section 11. 1.3 Understanding fens Deciding how best to manage and create fens depends on understanding how fens work, how fens relate to the wider landscape, and how past management has influenced fens and the wildlife they support. Topography, hydrology and geology all play important roles in determining how a fen develops and is maintained. It is not only the geographical location of a fen which matters but also the type of rock and the way land is managed elsewhere in the catchment through which water feeding the fen has passed. The different types of fen are manifest in terms of the mix of plant species and how these interact with each other, to provide structural niches in which other wildlife such as dragonflies and birds can flourish. Fens can be classified in a variety of ways, including the height and/or type of dominant plant species, for example short sedge fens and tall reed fens, but the type and stature of vegetation is intrinsically linked to other environmental factors. Fens are therefore most commonly defined by their association with particular landscape features, and according to the source of water which feeds the fen. Section 3: Understanding Fen Hydrology explains more about fen hydrology and different types of fen. Section 4: Understanding Fen Nutrients explains about the different types and sources of nutrient critical to fens and how the nutrient status of individual fens can be assessed. 9 Floodplain landscape of the Biebrza River in north-east Poland. The naturally occurring diversity of wetland habitats including fens, wet grassland, reed- bed and scrub reflect constantly changing natural processes such as fluctuating water- levels (M. Street). 1.4 Fen management and restoration Wetland habitats, including fens, change with time. Without intervention, first reeds and then trees such as willow establish around the edge of open water. Silt carried by water flowing into the fen is trapped by the reeds, scrub and trees, and speeds up the transition to drier habitat. In the place of open water, open fen forms, which in turn becomes wet woodland. Fens may also transform into other habitats such as raised bog or dry woodland. These processes are referred to by ecologists as succession, or sometimes as hydroseral succession, to link the process specifically to the sequence of changes from open water. In addition once fen vegetation is established the dead and decaying plant material can form peat; this process known as paludification. In the past, harvesting and use of reeds and other fen products helped keep fens open but as traditional crafts and management practices have ceased, trees have gradually taken over many open fens, producing a different landscape with less diverse wildlife habitats. 10 Guiding principles for fen management, restoration and creation – Maintain or create ‘the right fen in the right place’. This means the most appropriate type for the geo-hydrological setting. – Aim for diversity, not uniformity. Resist the temptation to create the same type of fen everywhere just because it is easy to do so. – Take account of the surroundings and neighbouring habitats, such as lowland bog, wet grassland and wet woodland, in order to complete eco-hydrological units. – Consider the site within the context of the wider landscape. Many of today’s small fen sites and other wetlands are remnants of what were once much more extensive wetland systems. Section 5: Fen Management and Restoration outlines some of the common problems associated with managing fens and provides a framework for deciding when intervention may be necessary to maintain wildlife interest.