Françoise Burel

Functional landscape heterogeneity and animal biodiversity in agricultural landscapes.

Biodiversity in agricultural landscapes can be increased with conversion of some production lands into more-natural- unmanaged or extensively managed - lands. However, it remains unknown to what extent biodiversity can be enhanced by altering landscape pattern without reducing agricultural production. We propose a framework for this problem, considering separately compositional heterogeneity (the number and proportions of different cover types) and configurational heterogeneity (the spatial arrangement of cover types). Cover type classification and mapping is based on species requirements, such as feeding and nesting, resulting in measures of functional landscape heterogeneity. We then identify three important questions: does biodiversity increase with (1) increasing heterogeneity of the more-natural areas, (2) increasing compositional heterogeneity of production cover types and (3) increasing configurational heterogeneity of production cover types? We discuss approaches for addressing these questions. Such studies should have high priority because biodiversity protection globally depends increasingly on maintaining biodiversity in human-dominated landscapes.

Why and how we should study field boundary biodiversity in an agrarian landscape context

Field boundaries are generally considered as important semi-natural environments in agrarian landscapes. The aim of this paper is to provide a methodological framework towards a holistic approach for field boundary studies. First, an overview of the successive milestones that have been passed in the history of hedgerow studies is given. These are classified a posteriori and then related to the succession of dominant ecological paradigms. Secondly, we show how former results have been used and integrated into a multiple scale approach involving agronomic and ecological studies in hedgerow network landscapes of western France. The hypothesis is that the main determinants of hedgerow biodiversity are related to farming activities. This hypothesis has been tested in three hedgerow network landscapes differing in their density of hedgerows and their relative abundance of grassland versus crops. The dominant agriculture of the region is dairy production, utilising grassland, maize and cereals. We focus on plant biodiversity and relate it to farming activities described from the boundary up to the landscape. The results show that the composition of the plant assemblages of the herb layer of field boundaries depends upon complex interactions between local structure, herb layer management, field use, farm types and landscape structure. The latter factors are related to the diversity of farming systems. Finally, the advantages of such an approach in terms of fundamental and applied landscape management aspects are discussed, showing how our framework of hedgerow studies expands by successive incorporation, rather than by rejection of former approaches. The main lesson is that it is necessary to capitalise on closer collaboration between ecologists and agronomists in order to stimulate future development of field boundary management and planning.

Hedgerows and Their Role in Agricultural Landscapes

Abstract Hedgerows, rows of trees or shrubs enclosing or separating fields, are man made. They are part of rural landscapes and should not be studied without considering the farming systems and the rural society as a whole. Their species composition depends on the history of the countryside, as well as current farming practices. Land use and boundary management play a major role in determining the floristic composition of hedgerows, and are strongly related to the grain size of the fields mosaic. Hedgerow networks, due to their rectilinear shape, and with their high degree of connection, enhance or interrupt many fluxes in the landscape. Hedgerows act as a corridor of movement and dispersal for many forest species, such as carabids, small mammals, and plants. On the other hand, hedgerows interrupt or slow down air fluxes and the propagules they carry. In the heterogeneous mosaic of fields and wooded patches, hedgerows often increase the functional connectivity of rural landscapes. The future of hedgerows...

Differential response of selected taxa to landscape context and agricultural intensification

Understanding the dynamics of biodiversity in changing agricultural landscapes is a goal for nature conservation and agricultural policies. Agriculture operates at several spatio-temporal levels from field to landscape, and induces differential response of communities according to their ecological traits. Reactions of several taxa to landscape and agricultural changes was conducted along landscape gradients in northern Brittany (France) gathering 14 sites. Landscapes ranged from fine grained areas, with a large proportion of permanent grasslands, wood and hedgerows, to coarse grained ones dominated by crops. Response of communities were either loss of species along the gradient (as for Diptera Chironomidae and Empididae), replacement (Coleoptera Carabidae) and no change in species composition (small mammals). In this paper, we present why these taxa react in such different ways according to their life history traits, their mobility patterns and to which parameters of landscape structure or agriculture intensification they are sensitive. Density of hedgerow networks, and permeability of individual hedgerows determine the spatial distribution of adults Diptera according to their flying ability. Mean body size of carabid beetles significantly decreases along the gradient of agricultural intensification, small species adapted to disturbance replacing large ones that are characteristic of stable habitats. The same small mammal species are found all along the two gradients, but their relative abundance is linked to the importance of crops versus more stable habitats in the landscape. n nWe concluded that species survival in those fine grained agricultural landscapes depends on processes operating at the site scale and defining habitat quality, and processes operating at the landscape and/or metapopulation scale such as landscape modifications in connectivity and habitat availability.

Response of the small mammal community to changes in western French agricultural landscapes

We studied the response of the small mammal community (rodents and shrews) to recent changes in agricultural systems of western French landscapes. Work was conducted on twelve sites representative of the diversity of farming systems in this region. The characteristics of small mammal assemblages in each site were assessed using Barn Owl (Tyto alba) pellet analysis. Relationships between small mammal data and landscape descriptors were performed through co-inertia analysis. Richness and specific composition of the small mammal community were not affected by the degree of cultivation but variations in species frequency could be observed. The prevalence of some species allowed us to distinguish three main assemblages which were characteristic of low, medium, and high intensified landscapes. Status and life traits of these species showed that intensification of agriculture has negative effects on density of rare and habitat-specialist species while it favours habitat-generalist species, some of them being known to exhibit fluctuating density. The two main ways of agricultural intensification (maize vs. other crops) did not show any significant relationships with species assemblages. Our results gave us the opportunity to suggest recommendations on agronomical and conservation problems that may arise from these changes of agriculture in western France.

Plant functional group composition and large-scale species richness in European agricultural landscapes

Abstract Question: Which are the plant functional groups respondcing most clearly to agricultural disturbances? Which are the relative roles of habitat availability, landscape configuration and agricultural land use intensity in affecting the functional composition and diversity of vascular plants in agricultural landscapes? Location: 25 agricultural landscape areas in seven European countries. Methods: We examined the plant species richness and abundance in 4 km × 4 km landscape study sites. The plant functional group classification was derived from the BIOLFLOR database. Factorial decomposition of functional groups was applied. Results: Natural habitat availability and low land use intensity supported the abundance and richness of perennials, sedges, pteridophytes and high nature quality indicator species. The abundance of clonal species, C and S strategists was also correlated with habitat area. An increasing density of field edges explained a decrease in richness of high nature quality species and an increase in richness of annual graminoids. Intensive agriculture enhanced the richness of annuals and low nature quality species. Conclusions: Habitat patch availability and habitat quality are the main drivers of functional group composition and plant species richness in European agricultural landscapes. Linear elements do not compensate for the loss of habitats, as they mostly support disturbance tolerant generalist species. In order to conserve vascular plant species diversity in agricultural landscapes, the protection and enlargement of existing patches of (semi-) natural habitats appears to be more effective than relying on the rescue effect of linear elements. This should be done in combination with appropriate agricultural management techniques to limit the effect of agrochemicals to the fields. Nomenclature: Tutin et al. (2001).

Landscape context and carabid beetles (Coleoptera: Carabidae) communities of hedgerows in western France

Dramatic changes have occurred in agricultural landscapes of western Europe since the 1950s. Their effects on biodiversity have been documented at local scales in terms of agricultural practices and management of uncultivated elements, more than at the landscape level. The highest diversity of agricultural landscape structure found in Brittany (France) is characterised by hedgerows surrounding arable fields and permanent grasslands. Some areas did not change much over a few decades, while others were totally transformed by agricultural intensification, field enlargement and removal of hedges. The present paper aimed at examining if this landscape context affected carabid beetles communities in hedgerows. In 11 sites of 1 km 2 each, land use diversity and heterogeneity, hedgerow connectivity and landscape openness were measured. Carabid beetles sampled in hedgerows were identified to species, and grouped in functional units. Multivariate analyses were used to relate the spatial distribution of insects to different parameters of landscape structure. The results show a significant relationship between landscape structure and carabid communities. Forest species were more abundant in dense hedgerow networks with a relatively high ratio of permanent grasslands. Landscape opening induced a shift in species composition; the relative abundance of large species decreased while small, mobile and more ubiquitous species were favoured. Two trajectories of landscape change were identified, which led to different responses in communities, the increase in maize for milk production opening the landscape far more than cereal crops associated with industrial pig or poultry production. Changes were most important in the latter case.

Temporal variability of connectivity in agricultural landscapes: do farming activities help?

In landscapes where natural habitats have been severely fragmented by intensive farming, survival of many species depends on connectivity among habitat patches. Spatio-temporal structure of agricultural landscapes depends on interactions between the physical environment and farming systems, within a socio-economic and historical background. The question is how incentives in agricultural policies may influence connectivity? May they be used to manage the land for biodiversity conservation? We used simulations based on property field maps to compare connectivity on the same landscape during seven years of crop succession for two dairy farming systems, one being representative of conventional systems of western France, the second one representative of systems undergoing intensification of production. Connectivity is a measure of landscape structure and species characteristics based on individual area requirements and dispersal distance. Models used are based on weighed distances, considering differential viscosity for different land uses. The results show that, for a given farming system, physical and field patterns constraints are such that landscape connectivity remains the same over years, while it is significantly different between the two farming systems. This is consistent with the recent input of policies to promote environmentally friendly farming systems, and confirms that policies must encounter the landscape level. The analysis also demonstrates that the localisation of forest patches, resulting from long term land cover changes, plays a central role in connectivity and overrides changes in agricultural land uses.

Role of habitat and landscape in structuring small mammal assemblages in hedgerow networks of contrasted farming landscapes in Brittany, France

In this study, we investigated the environmental factors driving small mammal (rodents and shrews) assemblages in permanent habitat patches in response to a gradient of agricultural intensification. Small mammals were sampled using a trapping standard method in the hedgerow networks of three contrasted landscapes differing by their level of land-use intensity and hedgerow network density (BOC1: slightly intensified; BOC2: moderately intensified and POL: highly intensified). We hypothesized that habitat and landscape characteristics have to be considered to understand the structure of local community. In that way, we carried out a multi-scale study using environmental variables ranging from local habitat (structure and composition of the hedgerows) to hedgerows neighbourhoods in a radius of 300xa0m (land cover and connectivity around hedges) and to landscape units (three sites). During 1xa0year, 24 hedgerows were sampled seven times, representing a total of 1,379 captures (86% of rodents and 14% of shrews) and eight species, dominated by the wood mouse (Apodemus sylvaticus) and the bank vole (Clethrionomys glareolus). Inter-site variability was significant and accounted for 18% of total variation in small mammal species abundances. But intra-site variability was also highlighted: species abundance profiles may differ greatly among hedgerows within a site. The more explanatory variables were identified at the different scales of the study: the landscape unit POL was shown to be an important factor in structuring the community, but the predominant factors explaining differences of abundances among hedgerows were about local habitat. In fact, the width of hedges and the tree species richness appeared to be significant and explaining the greatest part of the total variation of the small mammal community composition.

Ditch network sustains functional connectivity and influences patterns of gene flow in an intensive agricultural landscape.

In intensive agricultural landscapes, plant species previously relying on semi-natural habitats may persist as metapopulations within landscape linear elements. Maintenance of populations’ connectivity through pollen and seed dispersal is a key factor in species persistence in the face of substantial habitat loss. The goals of this study were to investigate the potential corridor role of ditches and to identify the landscape components that significantly impact patterns of gene flow among remnant populations. Using microsatellite loci, we explored the spatial genetic structure of two hydrochorous wetland plants exhibiting contrasting local abundance and different habitat requirements: the rare and regionally protected Oenanthe aquatica and the more commonly distributed Lycopus europaeus, in an 83u2009km2 agricultural lowland located in northern France. Both species exhibited a significant spatial genetic structure, along with substantial levels of genetic differentiation, especially for L. europaeus, which also expressed high levels of inbreeding. Isolation-by-distance analysis revealed enhanced gene flow along ditches, indicating their key role in effective seed and pollen dispersal. Our data also suggested that the configuration of the ditch network and the landscape elements significantly affected population genetic structure, with (i) species-specific scale effects on the genetic neighborhood and (ii) detrimental impact of human ditch management on genetic diversity, especially for O. aquatica. Altogether, these findings highlighted the key role of ditches in the maintenance of plant biodiversity in intensive agricultural landscapes with few remnant wetland habitats.