Report Number 627 The ecological impact of sweet chestnut coppice silviculture on former ancient, broadleaved woodland sites in south-east England English Nature Research Reports working today for nature tomorrow English Nature Research Reports Number 627 The ecological impact of sweet chestnut coppice silviculture on former ancient, broadleaved woodland sites in south-east England Peter Buckley and Ruth Howell Imperial College, Wye College, Ashford, Kent You may reproduce as many additional copies of this report as you like, provided such copies stipulate that copyright remains with English Nature, Northminster House, Peterborough PE1 1UA ISSN 0967-876X © Copyright English Nature 2004 Preface Sweet chestnut Castanea sativa is treated as an “honorary native” in some woods and as an undesirable alien in others. A considered view of its impact on nature conservation values has been hampered by the lack of an up-to-date review of its ecology. English Nature is grateful to the authors and sponsors of this report for permission to reproduce it in our research report series. Keith Kirby English Nature, Peterborough Acknowledgements We would like to acknowledge our two sponsors, Kent County Council and Gallagher Aggregates Limited1, whose joint financial support enabled this review. Particular thanks are due to their representatives, respectively Debbie Bartlett (Kent County Council) and Tom La Dell (Tom La Dell Landscape Architects) for their valuable advice, contributions and suggestions. Thanks must also go to the delegates who attended and contributed to the workshop held at Department of Agricultural Sciences campus of Imperial College in February 2003, particularly our invited speakers and workshop facilitators. We are grateful for contributions to our review report from Debbie Bartlett, David Rossney (ESUS Forestry & Woodlands Ltd), Ralph Harmer (Forestry Commission), Graham Bull (Forestry Commission), Keith Kirby (English Nature), John Badmin (Kent Field Club), David Gardner and Mark Parsons (Butterfly Conservation). We would also like to thank the Bat Conservation Trust for granting us permission to include four bat distribution maps, Nigel Braden and Karen Russell for their sweet chestnut distribution map and Pamela Howell for the title page and interleaf illustrations. 1 Gallagher Aggregates Ltd, Hermitage Quarry, Hermitage Lane, Maidstone, Kent ME16 9NT email: [email protected] Summary Sweet chestnut Castanea sativa was probably introduced into Britain over two millennia ago, since when its range has expanded steadily across southern England as a result of increasing domestication and naturalization. Initially valued for its nuts and timber properties, planting of pure chestnut stands for coppice accelerated sharply in the nineteenth century in response to strong hop-growing and fencing markets. These plantations were often located on sites of semi-natural, broadleaved woodlands that were comprehensively cleared of competing woody species. Current woodland census data underestimates the area of chestnut in Britain at c.19,000 ha, while the true area of chestnut-dominated woodland could be twice this extent. Chestnut is well adapted to a wide range of site and soil conditions normally occupied by mixed broadleaved woodland communities characterised by oak, hazel, birch and ash. Its ecological impact on these communities is reviewed according to the main taxonomic groups: vegetation, fungi, invertebrates, birds and mammals. An overall conclusion is that few, if any species recorded so far within these major groups are directly dependent on chestnut as a host. While chestnut does support a number of species that also occur on trees and shrubs comprising the equivalent native broadleaved community, the number and variety associated with the former appears to be lower, especially in monoculture stands. On the other hand, the maintenance of the coppice cycle in commercially viable chestnut crops can be beneficial to some notable species that are dependent upon young growth stages, such as fritillary butterflies and migrant birds, while the system of relatively small coupe sizes and extensive ride networks present in worked coppice adds diversity at the whole forest scale. However, as the uncertain future of markets for chestnut shows, there is no guarantee of consistent or continued working, except perhaps on sites already in nature conservation ownership. Where management incentives are available to diversify chestnut sites, alternatives include varying the rotation length, reducing the dominance of the chestnut canopy by stool removal and/or thinning, reintroducing native species, promoting stands to high forest and practising minimum intervention. These techniques are most appropriate on sites where chestnut substitution is recent, rather than where historical accounts and evidence on the ground confirm a long and continuous presence of the species. Apart from the effects of market uncertainty, the future status of chestnut will be determined by its resilience to new challenges from disease and climate change. The recent advance of chestnut blight Cryphonectria parasitica in northern Europe suggests strongly that it will extend its range into Britain; the impact could be to reduce the dominance of chestnut in woodlands in southern England. Conversely, scenarios predicted for climate warming during the remainder of the 21st century indicate that conditions favouring chestnut will be enhanced, causing it to become a more invasive and aggressive component of ancient woodland. A number of recommendations are made for further research and study. Contents Preface Acknowledgements Summary Part I – History, distribution and management ........................................................................13 1. Introduction..................................................................................................................15 1.1 Aim ..................................................................................................................15 1.2 Scope................................................................................................................15 2. History of sweet chestnut in the UK............................................................................16 2.1 Introduction of sweet chestnut into Britain......................................................16 2.2 How much sweet chestnut was planted?..........................................................17 2.3 Pre-twentieth century use and management of chestnut..................................18 3. The chestnut habitat .....................................................................................................19 3.1 Native distribution of chestnut.........................................................................19 3.2 Climatic tolerances...........................................................................................20 3.3 Ecological tolerance of chestnut in Britain......................................................20 3.4 Plant species richness of the chestnut communities ........................................25 4. Range and extent of sweet chestnut in Britain.............................................................25 5. Silviculture and management.......................................................................................29 5.1 Coppice management.......................................................................................29 5.1.1 Establishment and restocking ..............................................................29 5.1.2 Regrowth and cutting...........................................................................30 5.2 Coppice yield and markets...............................................................................31 5.3 Storing coppice................................................................................................34 5.4 High forest and timber .....................................................................................35 5.5 Other markets...................................................................................................35 5.5.1 Nuts......................................................................................................35 5.5.2 Edible fungi..........................................................................................36 5.6 Potential markets..............................................................................................36 Part II – Ecological effects of planting sweet chestnut............................................................37 6. Vegetation....................................................................................................................39 6.1 Plant species richness.......................................................................................39 6.2 Lichens.............................................................................................................40 7. Fungi ............................................................................................................................42 7.1 Fungal species diversity...................................................................................42 7.2 Fungal species of conservation concern in south-east England.......................44 7.2.1 Diversity...............................................................................................44 7.2.2 Summary..............................................................................................47 7.3 Ecology