Hedgerow Diversity: an International Perspective on Their Origin, Function and Management

Journal of Environmental Management (2000) 59, 000–000 doi:10.1006/jema.2000.0358, available online at http://www.idealibrary.com on Hedgerow diversity: An international perspective on their origin, function and management J. Baudry†*1, R. G. H. Bunce‡ and F. Burel§ A framework for the ecological study of hedgerows is given, before a short review of problems relating to their definition. Hedgerows have developed in response to the inherent physical and biological character of the region concerned, in conjunction with cultural factors. Traditionally, hedgerows were an important source of wood as well as other products, although such functions are in decline in many regions. They still have an important role in the landscape for soil protection and act as barriers and boundaries between management units. Although the closed landscapes of the Atlantic fringe, termed ‘bocage’ are often considered as the core of hedgerow distribution, there are many other regions, not only in Europe, but also elsewhere in the world with equally dense networks. It is concluded that a review of their distribution would be of great interest for the design of appropriate policies for landscape management and conservation of hedgerows. Such regions show marked differences in hedgerow character, species composition and the type of management and there is a degree of convergence between them. The diversity of hedgerows stems from their multiple origins and includes their role in the landscape, as well as their contribution to biodiversity and function. It is emphasised that hedgerows have often changed roles in history and current regulations for their protection must be based on sound science and a precise definition of their role and contribution to social objectives. 2000 Academic Press Keywords: hedgerows, landscape, diversity, management, products, distribution, functions, biodiversity. Introduction and loss of hedgerows. This paper explores the geographical distribution of hedgerows and provides a classification according to Hedgerows, or related structures such as their function in the landscape. It therefore Ł Corresponding author rows of trees or shrubs, are conspicuous could provide a stimulus for the definition landscape elements in many parts of the † Institute National de la of regulations for protection and manage- Recherche Agronomique, World. They are human-made features and ment. SAD-Armorique research have contrasting roles recognised by different Agriculturists have praised hedgerows for unit, 65, rue de people, from those who plant or let them Saint-Brieuc, 35042 their utility for centuries, (see Rozier, 1784). Rennes Cedex, France grow, to casual visitors and ecologists. Today, Geographers and ecologists have studied hedgerows are highly regarded primarily hedgerows for almost a century (Alexan- ‡ Institute of Terrestrial for their ecological and cultural values, for Ecology, Merlewood der, 1932; Bates, 1937). Geographers, ecolo- Research Station, example as recognised by the Hedgerow gists, and conservationists showed increased Grange-over-Sands, Regulation 1997 legislation in the UK. In interest in hedgerows and bocage land- Cumbria, LA11 6JU, UK the past other functions were dominant e.g. scapes in the 1950s and 1960s, when much § Centre National de la boundaries, shelter, sources of products and removal occurred. In Great Britain Pollard Recherche Scientifique, even as snow breaks by railways in Poland. Universite´ de Rennes 1, et al. (1974) and France INRA et al. (1976) UMR ECOBIO, Campus de The change and subsequent loss of past described important research programmes Beaulieu, 35042 Rennes functions are the main reasons for the threat that had been carried out. Although the pres- Cedex, France 1 Email address of corresponding author: jbaudry@ ence of hedgerows has long been recognised Received XX March 2000; roazhon.inra.fr in many parts of Europe, for example in accepted 26 June 2000 0301–4797/00/000000C00 $35.00/0 2000 Academic Press 2 J. Baudry et al. Germany and Switzerland, the majority of of the time a hedgerow is a field boundary research in the last two or three decades and its management forms part of farming concerns the Atlantic zone of western France activities. As we shall see, this human com- and Britain. Despite this narrow perception, ponent is essential in shaping hedgerows. So, hedgerows are actually important landmarks we define a hedgerow as a linear feature com- of human settlements and agricultural land- posed or shrubs and/or trees that forms part scapes throughout the world. However, the of a management unit. Different definitions description and distribution of hedgerows has may be used over the minimum length con- not yet been widely carried out, although sidered to be a hedgerow depending upon the Rackham (1988) has already pointed out that objectives of study e.g. the minor differences hedgerows do have a much wider distribu- between Barr et al. (1993) and Cooper and tion than many people realised. Shelterbelts McCann (1997). ‘Hedgerow’ is a generic term in prairie landscapes and fences in the trop- scientists use, but it also exists as in a vari- ics are well known linear features sharing ety of local names that are the product of the many characteristics with temperate zone cultural, technical and social values of the hedgerows, and are composed of trees and region concerned. This subject has been anal- shrubs. They are adjacent to agricultural ysed and debated in several social groups, fields and form networks in a similar struc- including scientists and others who are inter- ture to that seen in Europe, although they ested in the perception and language used are of different origin. to describe hedgerows (Oreszczyn and Lane, The continued and expanding interest in 1999). hedgerows stems from their ecological and The landscape elements we define as cultural value and because they act as refuges ‘hedgerow’ are, most of the time intercon- for species unable to exist elsewhere in farm- nected into networks. When it comes to land. They are also artefacts of vanishing analyse hedgerows, or to make decisions rural cultures. From a scientific point of view, on individual hedgerows, the question that the development of landscape ecology pro- arises is ‘where are the limits?’. For sur- vides new concepts, methods and theories to veys, evaluation and mapping for defining gain insight on hedgerow function and their the resource in a given area, one needs to ecological status (Forman and Baudry, 1984; define the ‘hedgerow unit’. Hedgerow inter- Burel, 1996). Studies of cultural landscapes sections are identifiable and provide tangible (Rackham, 1986) stress the diversity of tree points (a hedgerow unit is defined as the management, related to technical, and social segment of hedgerows between two intersec- factors of hedgerows, as well as other functions), but other measurements are possible. tions e.g. protection from erosion. For example, Baudry and Thenail (1999) have used the limits of land-use units, i.e. there must be a single type of land use What is a hedgerow? on one side of a hedgerow. This definition enabled them to make links between land use, land managers and hedgerow character- Definition istics. In contrast, the Institute of Terrestrial Ecology (ITE) use ‘homogeneous’ units for Few studies attempt to give a formal defini- the countryside survey with a hedge being tion of what constitutes a ‘hedgerow’ beyond described as a boundary, or part of a bound- the statement that it is a row of shrubs and/or ary which comprises a row of bushes or low trees managed in various ways (although trees growing close together, and which have Pollard et al. (1974) do devote a chapter been managed through cutting to maintain a to hedgerow description). We propose that more-or-less dense linear barrier (Barr et al., although any row of woody vegetation can be 1993). A minimum length of 20 m is used a corridor or a barrier for ecological processes, together with description in terms of code it may not be a ‘hedgerow’ if it is not managed. combinations to define the character of the A hedgerow, whether planted or spontaneous, hedge for example, height and proportion of always has a human component and is more gaps. The length of each boundary segment or less managed to provide control and to pre- is determined by the constancy of a combi- vent its expansion into adjacent fields. Most nation of codes along the length; where any Hedgerow diversity 3 one description differs, then a new length is but the parliamentary Enclosure acts grad- demarcated, and a new combination of codes ually replaced these by a chequer-board of applied. Other definitions have been used e.g. small fields enclosed by hedges of hawthorn. Cooper and McCann (1997) but work in ITE These hedges were planted, usually with has shown that a precise definition of the ditch along side in the midlands, but often delimitation of hedgerows can enable com- on a low bank in the north and west of parisons to be made between independent England. Trees were also often planted in studies. the new hedges. Rackham (1986) gives fur- ther details of how the enclosures affected the landscape, and also points out that in Origin and distribution north and west Britain the process of enclosure is not as well documented as the mid- French geographers use the word ‘bocage’ lands and the south. In northwest England to mean a landscape where hedgerows are hedges by old roads often have many woody characteristic features. Bocage has been species, whilst those across fields are virtu- used some time in English in the past, ally pure hawthorn, suggesting that these are and here we use it because the expres- the planted Enclosure hedges (pers. Obser- sion ‘hedgerow network landscape’ is inele- vation RGHB). Therefore, the view that gant. We approach the distribution of bocage, Britain has one of the most dense ancient rather than hedgerows, which are of minor hedge networks in Europe is not strictly importance if few, are present in a land- true—rather the majority of hedges are rela- scape.

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