Claudine Thenail

Comparative biodiversity along a gradient of agricultural landscapes

The aim of this study is to compare biodivemity in contrasted landscape units within a small region. In western France agricultural intensification leads to changes in landscape structure: permanent grasslands are ploughed, fields enlarged and surrounding hedgerows removed or deteriorated, brooks are straightened and cleaned. South of Mont Saint Michel Bay, four landscape units have been identified along an intensi- fication gradient. Several taxonomic groups (small mammals, birds, insects and plants) have been used to evaluate the characteristics of biodiver- sity along this gradient. The hypothesis that intensification of agricultural practices lead to changes in biodiversity has been tested. Biodiversity is measured by the species richness, Shannons diversity index, equitability and similarity indexes. Our results show that intensification of agriculture does not always lead to a decrease in species richness, but to several functional responses according to taxonomic groups, either no modification, or stability by replacement of species, or loss of species. For most of the studied taxo- nomic groups species richness does not vary greatly along the gradient. Depending on the landscape structure and farming systems this gradient is probably truncated and does not allow to show major changes in species richness. An alternative hypothesis is that used indexes are not sensitive enough to reveal changes in biodiversity. Nevertheless, similarity indexes reveal that sensitivity to changes varies, invertebrates being more likely to perceive the dynamics of the landscapes studied than vertebrates or plants. These points have to be taken into consideration when elaborating policies for sustainable agriculture or nature conservation. 0 Elsevier, Paris

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.

A holistic landscape ecological study of the interactions between farming activities and ecological patterns in Brittany, France

Abstract We present a holistic analysis of the interactions of farming activities and ecological patterns within a gradient of landscape structure. This gradient is represented by three landscapes that grade from a dense hedgerow network landscape to an open landscape. These landscapes differ in both the type of farms (though most are dairy farms) and the type of hedgerow. Differences in hedgerow structure are correlated to adjacent land-use and to differences in farming systems. The grain of the landscapes, measured by the area of land at various distances from dense hedgerows is also different from one landscape to another. Ecological patterns are assessed by plant species distribution. Variations in the plant species composition of field margins is related to hedgerow structure, adjacent land-use and landscapes. The combination of hierarchical approaches of both farming systems and ecological systems through landscape elements and patterns proves to be a promising avenue to understand and manage the interactions between the two systems.

Variation of farm spatial land use pattern according to the structure of the hedgerow network (bocage) landscape: a case study in northeast Brittany

Abstract The spatial pattern of fields and associated land use types in farms contributes to the landscape and its associated ecological dynamics. This pattern is also a component of farm management and development. This paper deals with modeling the land use spatial organization in farms according to these dual criteria. The hypothesis is tested that the location of farms along a gradient of bocage landscape—gradient of decreasing hedgerows density and increasing field size—influences their inner land use organization. The tests were based on mutual information and provided a hierarchy of driving factors of land use allocation in farms, as well as a classification of combinations of land use and field types. Three bocage sites—A, dense; B, intermediate; and C, open bocage—were chosen in northeast Brittany (France), on a 20xa0km2 micro-region of conventional dairy production based on maize (Zea mays L.), grassland and winter cereals, mainly wheat (Triticum spp.). In this context, land use allocation in a farm was better explained by the characteristics of the farm territory, i.e. the actual land used by a single farm, rather than by the characteristics of the farm household/enterprise, as defined by production, socioeconomic and technical features. Farms of the open bocage showed marked concentric patterns of land use away from the farmsteads, involving progressively pastures used by dairy cows, fodder crops, pastures used by livestock and cash crops. In these farms, there was a pronounced differentiation of the fields that held simultaneously constraints of surrounding hedgerows, small size and hydromorphy. Farms of the dense bocage site were more fragmented and constraints were distributed more diversely through fields, so that land use allocation was not optimized according to the distance from the farmstead. The concentric pattern of land use was therefore distorted in these farms. At a landscape level, such distortions led to a land use mosaic dominated by large patches of specialized fields in the open bocage, and to a fine grain and heterogeneous land use mosaic in the dense bocage. This study therefore demonstrated how the structure of the farm territory in different bocage landscapes has a major influence on land use allocation in farms. The results emphasize the interaction between land use and land structuring in farm quality of management, which in turn influences the landscape structure.

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.

Landscape agronomy: a new field for addressing agricultural landscape dynamics

Landscape dynamics increasingly challenge agronomists to explain how and why agricultural landscapes are designed and managed by farmers. Nevertheless, agronomy is rarely included in the wide range of disciplines involved in landscape research. In this paper, we describe how landscape agronomy can help explain the relationship between farming systems and agricultural landscape dynamics. For this, we propose a conceptual model of agricultural landscape dynamics that illustrates the specific contribution of agronomy to landscape research. This model describes the relationship between three elements: farming practices, landscape patterns and natural resources. It can stimulate agronomists to deal with research issues in agricultural landscape dynamics and enhance the interdisciplinary integration of farming systems in wider landscape research. On these premises, we discuss the main research issues that will benefit from an active involvement of agronomy, to understand, but also to assess landscape dynamics and to design relevant decision support systems.

Agricultural systems and landscape patterns : how can we build a relationship ?

We compare the landscape structure generated by the farming systems of two French regions. The system of production and the resulting farm functioning appears to be a major factor in landscape organisation. More emphasis should be put on farming systems studies to enhance our understanding of landscape dynamics and associated ecological processes.

15N-Nitrate signature in low-order streams : effects of land cover and agricultural practices

Many studies have shown that intensive agricultural practices significantly increase the nitrogen concentration of stream surface waters, but it remains difficult to identify, quantify, and differentiate between terrestrial and in-stream sources or sinks of nitrogen, and rates of transformation. In this study we used the delta15N-NO3 signature in a watershed dominated by agriculture as an integrating marker to trace (1) the effects of the land cover and agricultural practices on stream-water N concentration in the upstream area of the hydrographic network, (2) influence of the in-stream processes on the NO3-N loads at the reach scale (100 m and 1000 m long), and (3) changes in delta15N-NO3 signature with increasing stream order (from first to third order). This study suggests that land cover and fertilization practices were the major determinants of delta15N-NO3 signature in first-order streams. NO3-N loads and delta15N-NO3 signature increased with fertilization intensity. Small changes in delta15N-NO3 signature and minor inputs of groundwater were observed along both types of reaches, suggesting the NO3-N load was slightly influenced by in-stream processes. The variability of NO3-N concentrations and delta15N signature decreased with increasing stream order, and the delta15N signature was positively correlated with watershed areas devoted to crops, supporting a dominant effect of agriculture compared to the effect of in-stream N processing. Consequently, land cover and fertilization practices are integrated in the natural isotopic signal at the third-order stream scale. The GIS analysis of the land cover coupled with natural-abundance isotope signature (delta15N) represents a potential tool to evaluate the effects of agricultural practices in rural catchments and the consequences of future changes in management policies at the regional scale.

Interaction between farming systems, riparian zones, and landscape patterns: a case study in Western France

We analyze the factors driving land use within and outside riparian zones in four small (about 800 ha) watersheds in Brittany. The results show a difference between riparian and non-riparian zones (less used for grassland), but other factors are also important, such as field size or farm management type. In large farms, small fields are easily abandoned. A multivariate analysis with farm and field characteristics explains 30% of land use variation. Our results suggest that farm type deflects land use from the regional mode, so it is important, in the implementation of environmental zoning, to assess constraints at the farm level.

Weed dispersal by farming at various spatial scales. A review

Reducing pesticide use in agriculture is necessary to preserve natural resources. However, pest control without pesticides is a challenging issue. In particular, weed infestation may cause severe losses of crop yield. Weeds have been traditionally managed solely at the field level. However, larger scales must be considered because invasive and herbicide-tolerant weeds are spreading over larger scales. This review discusses three spatial scales at which agricultural management might affect the dispersal of weeds and, in turn, their distribution and abundance in agricultural fields. The main points are: (1) at the field level, crop and margin management impact mass effect, i.e., local exchanges between the field margin and the cultivated field; (2) at the farm level crop allocation, the management of field boundaries and agricultural circulation in the farm strongly impact the intensity and direction of weed dispersal; and (3) at the landscape level, the spatial farms distribution controls the distribution of weed habitat and, in turn, landscape species pool and long-distance weed dispersal. We conclude that weed dispersal is driven by agricultural management at multiple scales. Weed scientists should thus extend their view on weed dispersal from within-field scales to among-field and landscape scales.