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Guidelines for hedge management to improve the conservation value of different types of hedge

DEFRA Project BD2102

Abstract

Species-rich hedges have an approved Habitat Action Plan under the UK Biodiversity Action Plan. Hedgerows are a semi-natural feature of lowland agricultural landscapes in Britain, and are important as refugia for plant diversity and support many taxa, including farmland bird species. At both extremes of over-management and lack of management, reduced diversity may occur in hedgerows. However, little scientific information on the impacts of current hedge management, based on intensive use of flail cutting is available. This project has investigated these impacts on hedge growth and fruiting, the associated herbaceous flora and the insect fauna. An experimental approach using designed and replicated treatments of cutting frequency and timing (September and February) was implemented, with independent experiments on representative hedges across southern Britain. Subsidiary experiments on methods of regenerating species-poor hedge bases were implemented on arable and grass hedge bases. The advantages of relaxing annual hedge cutting for berry production were shown as expected. However, the invertebrate data, the first extensive study of trimmed hedges, showed that reactions to hedge cutting were complex. In contrast to perceived wisdom, winter cutting may have adverse effects on some groups and may reduce subsequent berry production on biennially-cut hedges. Attention to the herbaceous flora associated with hedges is important. Rotational management of hedges across farms is indicated, requiring a formal planSpatial variationThere is considerable variation in shrubs, herbaceous species and insects along most hedges. There are indications that variability in the flora influences the insect taxa along hedges, though further work is required to elucidate causal patterns. Particular plant species, such as nettle and cleavers, ProjecttitleGuidelines for hedge management to improve the conservation value of different types of hedgeMAFFproject codeBD2102CSG 15 (1/00)2may have large influences on insect taxa. As would be expected, insect diversity is positively related to plant diversity. Whilst the herbaceous flora is not related to the shrub component of hedges, both are influenced by local environmental variables. Berry productionBerries are produced on second year growth of woody species. Hedges that are left uncut for more than a year produce many more berries than annually-trimmed hedges. The longer the hedge is left, the more berries are produced. However, when these sections are left for three years, berry production in the year after cutting is particularly low. Hedges that are cut on a biennial cycle may be cut in either February or September. September cutting will remove the many berries produced in the second year before winter, but subsequent berry production is greater than on February-cut sections (see on for effects of February cutting on invertebrate larvae). Fruiting in woody species is variable between years and along hedges. Blossom may be damaged by late frosts. There may be genetic variation amongst individuals. Rosa canina (dog rose) acts like woody shrub species in its response to frequency of cutting. Rubus fruticosus (bramble) and other deciduous climbing plants are less affected by cutting frequency, though September cutting may reduce fruiting. Mixed species hedges are likely to give more consistent berry supply.Herbaceous and shrub floraNo significant effects of cutting treatments on numbers of species in the hedge or hedge base were shown. No significant effects on the herbaceous communities were shown using multivariate analyses. Analyses of individual herbaceous species might reveal more subtle effects associated with the change in width of the hedge relative to the verge, but no consistent effects have been established.InvertebratesUncut sections of hedge support greater numbers of some insect taxa, for example psyllids (plant lice). Nevertheless, there is evidence that cutting enhances the numbers of some taxa, notably herbivores and detritivores such as the Collembola and Thysanoptera (thrips). This may be a response to stimulated hedge growth. Increased number of herbivores is likely to enhance predator and parasitoid populations. Contrary to expectations, cutting in February reduces numbers of Lepidoptera (moths and butterflies) and possibly Diptera (flies) in the following summer, in comparison with September hedge cutting. These reductions may be of significance for birds. Hedge laying can give high taxonomic diversity as well as high total invertebrate abundance as the hedge regrows. This may be a reflection of stimulated hedge growth and good physical structure. Overwintering studies reveal that most invertebrates occur in the base of hedges as adults and larvae and include many groups found in the shrub layer in summer. Regenerating hedge basesIn degraded arable hedge bases, sowing seed mixtures to re-establish a diverse perennial flora can be successful. In grassland, seed mixtures were less successful and natural regeneration techniques are probably more appropriate. Reducing fertiliser contamination of the hedge base may help maintain plant diversity. Where annual weeds dominate the herbaceous flora, selective herbicides can be used. Where annual weeds smother the hedge, the insect diversity is correspondingly low in both the verge and the hedge above. Insect diversity is positively correlated with plant diversity. Therefore, to enhance the diversity of the hedgerow, both the hedge and the hedge base need to be managed sympathetically.Implications for birds and managementA mixture of hedge management regimes is likely to provide the best resources for farmland birds. Larger hedges favour bird diversity. Rotational cutting at less than an annual frequency should allow berries to be available during the winter. As February cutting may reduce some insect ProjecttitleGuidelines for hedge management to improve the conservation value of different types of hedgeMAFFproject codeBD2102CSG 15 (1/00)3numbers, but is essential for berries to be carried into the winter from the previous season, a mixture of cutting times is appropriate. Studies on the yields of adjacent crops did not show significant effects of hedge management. Measures of cutting time showed that there were advantages in leaving hedges for more that a year before cutting, in terms of the total time taken to cut over the cutting cycle. Thus there are cost advantages in relaxing hedge cutting from an annual trimming regime. ProjecttitleGuidelines for hedge management to improve the conservation value of different types of hedgeMAFFproject codeBD2102CSG 15 (1/00)4Scientific report (maximum 20 sides A4)Guidelines for hedge management to improve the conservation value of different types of hedgeBased on results of DEFRA Project BD2102M.J. Maudsley, E.J.P. Marshall*, T.M. WestIACR – Long Ashton Research Station, Department of Agricultural Sciences, University of Bristol, Long Ashton, Bristol BS41 9AF, UK*Marshall Agroecology Ltd, 2 Nut Tree Cottages, Barton, Winscombe, Somerset BS25 1DU. Tel: 01934 844844. E-mail: jon.marshall@agroecol.co.uk ; URL: http://www.agroecol.co.ukBackgroundSpecies-rich hedges have an approved Habitat Action Plan under the UK Biodiversity Action Plan, reflecting their importance for wildlife conservation and landscape. Hedgerows are a noted semi-natural feature of lowland agricultural landscapes in Britain, and are important as refugia for plant diversity and support many taxa of fauna, including farmland bird species. The cultural importance of hedges is reflected in their protection under the UK Hedgerow Regulations. At the two extremes of over-management and lack of management, reduced diversity may occur in hedgerows. British hedges have been divided into eleven categories according to the dominant shrub species present. The four major types are a) hawthorn dominant, b) mixed hawthorn, c) mixed hazel dominant and d) blackthorn predominant. There are also a number of other types, such as elm and gorse hedges, some of which are specific to different areas, for example the beech hedges on banks in Devon. Current management of hedges is based on trimming with flail cutters. The traditional techniques of laying are largely abandoned on the basis of cost, though hedge laying societies maintain the skill in many parts of the country. Work by FWAG has produced some useful data on the techniques that may be used for hedge management. In particular, a reduction in frequency of trimming to biennial cutting has benefits for wildlife. These results require further confirmation on different hedge types in different conditions. The timing of cutting will certainly affect fruiting in shrubs. Arable farmers try to trim hedges after crop harvest in early autumn, when access to field margins is easy. Grassland farmers tend to trim hedges earlier in the year. In previous times, hedge management was a winter operation, when farm labour was available. Advice on the management of hedges has been available for many years. An important aim of this project was to update this advice to include aspects of the best maintenance and to increase farmland biodiversity. Although there is a wide variety of advisory material available to farmers and agricultural advisors, there is relatively little quantified, scientific information on the impacts of current hedge management on farmland wildlife.Hedgerow ProtectionThe Hedgerow Regulations were introduced in England and Wales in 1997 in order to protect this characteristic element of the British countryside. Landowners are no longer allowed to remove hedges, except with the approval of the local authority. If the hedge is of value, as defined under the regulations, for wildlife, history or landscape, then the hedge will be protected. It is estimated that at least one fifth of the hedges in England and Wales fall under the definitions and are protected. Currently, the regulations are being reviewed.The following is extracted from the DEFRA website:http://www.defra.gov.uk/wildlife-countryside/rddteam/rddthf.htm ProjecttitleGuidelines for hedge management to improve the conservation value of different types of hedgeMAFFproject codeBD21025Under the Hedgerows Regulations 1997, it is against the law to remove most countryside hedges without first getting the permission of your local council.A leaflet -The Hedgerows Regulations: Your Question Answered- provides a brief summary of the law (available from DETR Free Literature). More detailed guidance is in The Hedgerows Regulations 1997: A Guide to the Law and Good Practice (£5.50 from DETR Publication Sales Centre). Neither of these publications are currently on the DEFRA website.The Regulations have been reviewed by a group of experts, who reported on their ideas for improving the system of hedgerow protection in 1998. A free summary of their report, published by the then Department for Environment, Transport and the Regions, has been published and is available online (or by calling 0870 1226 236). Full report, priced £10, can be obtained from Unit 21, Goldthorpe Industrial Estate, Rotherham, S63 9BL, telephone 01709 891318.Results of research into the review proposals, published in 1999, will help to inform decisions on how the current Regulations should be revised. Hard copies of this research report cost £15 from Unit 21, Goldthorpe Industrial Estate, Rotherham, S63 9BL, telephone 01709 891318.Outline and experimental designMany previous studies, have focussed on correlative studies between different hedgerows, e.g. between bird species and hedgerow variables. However, this project uses an experimental approach in order to reveal thespecific role of cutting management, and has investigated the impacts on hedge growth and fruiting, the associated herbaceous flora and the insect fauna. Manipulated and replicated treatments of cutting frequency (annual, biennial and triennial) and timing (September and February) were implemented, with independent experiments on representative hedges across southern Britain (Table 1). All sites except one had a history of annual flail cutting. The remaining site (Leicestershire) had a hawthorn hedge that had been uncut for four years prior to the experiment. Two hedge regeneration techniques, coppicing and laying, were included in the treatments at this site. Subsidiary experiments on methods of regenerating the herbaceous flora of species-poor hedge bases were implemented on arable and grass hedge bases.Table 1. Details of hedge study sites established in 1996 and 1997.SiteHedge typeFarm typeNo. of plotsFrequency treatmentsHampshireMixed hawthornArable211/1; 1/2; 1/3; uncutBuckinghamshireHawthorn/ dog roseArable181/1; 1/2; 1/3NorfolkHawthorn/ mapleArable151/1; 1/2; uncutLeicestershireHawthorn dominantArable151/1; layed; coppiced; uncutSomerset1Blackthorn dominantGrassland151/1; 1/2; uncutPowys, WalesMixed hazelGrassland151/1; 1/2; uncutExmoorBeech dominantGrassland151/1; 1/2; uncut 1/1 = annually cut; 1/2 = biennially cut; 1/3 = triennially cut; 1abandoned in 1998. ProjecttitleGuidelines for hedge management to improve the conservation value of different types of hedgeMAFFproject codeBD21026Research findings and management implicationsHedgerow berriesBerries are an important winter food supply for a wide range of farmland bird and small mammal species. Therefore increasing the abundance and availability of berries in hedges is a desirable conservation target. Larger wintering birds will feed on a range of berry types in hedges, but some specialisation amongst different bird species also exists. Most hawthorn berries are generally removed by early December; other species may be available longer.In woody hedge species, such as hawthorn (Crataegus monogyna), berries are produced on second year growth. Thus hedges that are left uncut for one year or more produce many more berries than annually-trimmed hedges. In contrast to some current management advice, this was found to be equally so for both September and February cutting times. Hedge cutting in September removes formed berries directly, whereas cutting annually in late winter reduces flowering and thus largely prevents autumn fruit-set. As there are differences in when berries are produced depending on the time of the cut (September vs. February), hedges cut on a biennial cycle must be cut at the same time each year. In general the longer the hedge is left, the more berries are produced on woody hedge plants. However, in hedge sections left unmanaged for three years (or more), berry production in the year after eventual cutting is particularly low. Coppicing, and to a significantly lesser extent laying, reduces hawthorn berry production in the immediate following years. However, these are long-term management techniques and berry numbers would be expected to increase with time.Bramble (Rubus fruticosus) and other deciduous climbing plants are less affected by cutting frequency, and there is evidence that regular management (including annual trimming) is beneficial for fruit production. September cutting significantly reduces availability of these berries in the autumn. Management practice may need to reflect such responses where bramble is dominant, and/or where the conservation of a particular bird species that feeds on these types of fruit is targeted.Fruiting in woody species is highly variable between years and along individual hedges. Summer flowering species such as bramble are much more consistent in the amount of berries produced each year and per area of plant. Rosa canina (dog rose) also has low variability in berry production, but generally acts like woody shrub species in its response to frequency and timing of cutting. Variation is likely to be a combination of genetic control and environmental influences. Therefore local provenance hedge material may present berry producing hedge plants best adapted to regional conditions. Mixed species hedgerows will provide more consistent berry availability each year, but not necessarily highest numbers of berries per length of hedge.?Avoid large-scale annual trimming as this drastically reduces the availability of berries on woody hedge species. ?February cutting is not necessarily better for berry production than September cutting.?Hedges uncut for longer produce more berries on shrubby plant species.?Berry production in bramble is enhanced by regular management (at least biennial cutting)

Author(s): Maudsley, MJ, Marshall, EJP, West, TM

Journal: DEFRA Project BD2102

Year: 2000

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