Landscape context and carabid beetles (Coleoptera: Carabidae) communities of hedgerows in western France
Introduction
Agricultural landscapes of western France used to be characterised by the presence of hedgerow networks (Baudry et al., 2000). They developed over many centuries, and their density (m/ha) peaked towards the end of the 19th century. Intensification in land use at the end of World War II led to drastic changes in landscape structure and composition: removal of hedgerows and small woodlots (Leonard and Cobham, 1977, Agger and Brandt, 1988, Meeus, 1990), introduction of new crops, agricultural practices and farming systems (Canévet, 1992). All these changes influence the dynamics of biodiversity in agricultural landscapes (Paoletti and Pimentel, 1992, McLaughlin and Mineau, 1995, Lindblach, 1999). Few studies have considered the landscape level (Burel et al., 1998, Duelli et al., 1999, Thenail et al., 1997). Within the framework of the Rio convention and of the European Common Agricultural Policy, it is a challenge to maintain and/or restore biodiversity in agricultural landscapes and to identify parameters that control it at the landscape level (Huston, 1995).
Agricultural landscapes are more than patches in a neutral matrix of crops (Burel and Baudry, 1995, Verboom and Van Apeldoorn, 1990, Bennett, 1990, With and Crist, 1995, Hanski, 1999), and the role of permanent or semi-permanent structures is essential to maintain biodiversity in many western European landscapes (Baudry, 1988, Burel, 1996, Wratten and Thomas, 1990). Some specialist species are restricted to field boundaries and uncultivated patches (Forman and Baudry, 1984, Paillat and Butet, 1996). Many species require a variety of habitats and use alternatively crops and uncultivated areas during their life cycle (Tucker, 1997, Delettre et al., 1998, Morvan et al., 1994). Undisturbed landscape elements serve as refuges (Ouin et al., 2000) and provide sources for recolonising habitats which have been disturbed (Dennis and Fry, 1992).
The conservation, restoration and management of hedgerows is of concern in many parts of Europe. Species diversity in hedgerows has been related to abiotic conditions (Burel, 1996), boundary structure (Pollard et al., 1974, Delettre and Morvan, 2000, INRA et al., 1976) and composition (Cameron et al., 1980, Forman and Baudry, 1984). Land use adjacent to the margin also plays an important role (Parish et al., 1994, Jouin and Baudry, 1998). Few papers have dealt with the hypothesis that landscape heterogeneity (Turner and Gardner, 1991) could influence species assemblages in landscape elements, e.g. that two hedgerows of similar vegetation structure and under identical land use, may differ in species composition if they are located in contrasted landscapes.
Though in the 1950s Brittany had a difficult economic situation, it is now in the lead in Europe for productions of pork, milk and poultry. Agriculture has shifted from polyculture and husbandry to industrial production of milk, meat, and fodder crop. Agricultural practices have changed frequently, the use of fertilisers and pesticides is important and there is a large surplus of organic matter.
Field enlargement led to a decrease in woody habitat, landscape connectivity, and homogeneity (Baudry and Burel, 1985, Burel and Baudry, 1990), while the average vegetation quality of hedgerows decreased (Barr, 1993). Dense hedgerows only remained around permanent grassland, fallow, and along streams (Baudry et al., 2000).
At the community level, invertebrates are more sensitive to changes than plants and vertebrates (Burel et al., 1998). Carabid beetles have been extensively studied (Petit and Usher, 1998, Kromp, 1999); some forest species use hedgerows as corridors for dispersal (Burel and Baudry, 1989) whereas many species overwinter in banks and hedgerows (Sotherton, 1985). Intensification in agricultural practices leads to a shift from forest specialists species to more ubiquitous ones, adapted to disturbances (Burel et al., 1998). Forest species are favoured by a dense herbaceous layer and a continuous tree layer (Burel and Baudry, 1989).
The present study aimed at testing the interactions between the landscape context and species assemblages in permanent elements (hedgerow network) based on data collected on a gradient of farming landscapes. The main objective was to evaluate how factors such as landscape opening, decrease in network connectivity and agricultural intensification affected carabid beetles assemblages in hedgerows.
Section snippets
Study area
The study took place in the Department of Côtes d’Armor (Brittany, western France). Biological data were collected from different landscape units with hedgerow networks. The arable matrix included permanent and temporary grasslands and a variety of crop productions.
Dairy production from fodder crops dominates largely in the region, and has increased from 47% in 1970 to 58% in 1988. Nowadays, less than a third of arable land is devoted to permanent grassland which continues to decrease (19.5% in
Results
The first factorial plane (F1×F2) of the COA performed on species data accounted for 48.6% of the total inertia. As reflected by the COA projection onto the first co-inertia plane (Fig. 2), the first factorial axis (F1) was mainly defined by Brachinus sclopeta (Fabr.) [BRSC] usually found in shaded and moist areas, and Agonum dorsale (Pont.) [AGDO], generally found in cultivated fields, as opposed to Nebria brevicollis (Fabr.) [NEBR] a woodland species. On the second axis (F2), the common
Discussion
Changes in agricultural practices have induced a decrease in carabid beetles abundance and a shift in community composition according to type and intensity of disturbance. Different subsets of species resulted from different management regimes although several species were observed at all sites.
The results showed that landscape significantly influenced the species assemblages in landscape elements. Such effect of the landscape context on biodiversity has already been shown in other agricultural
Acknowledgements
N. Millan de la Peña has been supported by a grant of the Mexican government (CONACYT) during her Ph.D. work in France. The Conseil Général des Côtes d’Armor provided fund for this study. We thank A. Georges and P. Fouillet for updating the nomenclature of the carabid beetles, and anonymous reviewers for their help and comments. We also thank Y. Rantier, V. Rescan, D. Volland, P. Salliou and A. Wolff for their technical assistance.
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