Bees provide a vital pollination service to many important crops and wildflowers yet are experiencing population declines across European and North American agricultural landscapes. The conservation of bee communities on farmland is a priority of the UK agri-environment schemes, which support pollinators through the provision of natural and semi-natural habitat, foraging resources and nesting sites. Data are needed to evaluate the effectiveness of these interventions in supporting bee communities and to allow the refinement of effective, evidence-based policy. This thesis examines the effectiveness of agri-environment management, though the provision of natural habitat, foraging resources and nesting sites, in supporting solitary bees, an important group of pollinators of which there are 250 species in the UK. Cavity nesting solitary bees and wasps were surveyed on 19 farms situated across central southern England, ranging from farms under no agri-environment scheme, to farms showcasing higher-level agri-environment management. Data on bee and wasp communities was collected by deploying solitary bee nest boxes. These nest boxes are marketed widely as nesting resources for solitary bees and are provided to farmers as part of Higher Level agri-environment schemes. Over the course of the study, 4002 solitary bees and wasps, comprising 10 species, were recorded. Natural Habitat: A positive relationship was identified between the abundance and species richness of bees and wasps and the proportion of natural habitat across farms. The availability of natural habitat also had a positive influence on the structural stability of bee and wasp parasitism networks; a positive association was identified with network link density. Link density measures the mean number of links per species within a network. Higher measures of link density are believed to confer greater resilience to species loss as individuals have more flexibility to switch interaction partner, limiting the risk of a cascade of secondary species extinctions. This set of results is encouraging, suggesting that the natural habitat types being promoted are effective in supporting solitary bee and wasp communities. Foraging resources: Examination of bee foraging preferences, through next generation sequencing of brood cell pollen DNA, demonstrated that the agri-environment scheme sown wildflower mixes do not support the foraging requirements of solitary bees effectively. Of the 15 plants included currently in the wildflower mixes that were recorded as present on the study farms, pollen from only one species, Ranunculus acris, was used by the bees. Rosa canina was identified as the most popular forage plant. The leaves of this species are also a preferred nesting material for Megachile leafcutter bees, providing strong justification for the inclusion of R. canina within the selection of hedgerow plants encouraged by agri-environment schemes. Tripleurospermum inodorum and Trifolium repens were also identified as good candidates for inclusion in wildflower seed mixtures. Nesting sites: A strong positive relationship between the density of solitary bee nest boxes and the rate of brood cell parasitism was identified, indicating that a high local density of nest boxes may expose bee larvae to a higher risk of parasitism. An enhanced risk of larval mortality could counteract the benefit of additional nest site provision. No significant effect of nest box provision on nest box colonization was identified across these study sites, suggesting that their placement across landscapes to encourage more pollinators may be counter-productive. It would be prudent to advise, given the results of this study, for the provision of a small number of dispersed nest boxes, this might more accurately mimic the availability of nesting resources in nature and reduce the risk of enhanced parasitism rates.

Concern over unexplained population declines in the common toad (Bufo bufo) has led to it being recognised as a priority species for conservation research. The general consensus among herpetologists is that the most important cause of the declines seen as part of a global amphibian extinction crisis is habitat loss and degradation. The aim of thesis is to investigate the effect of habitat availability and quality on common toad populations in the United Kingdom, with a particular emphasis on the effect of land under agricultural use. I use occupancy modelling, resource selection function modelling and genetic techniques to determine the effects of both terrestrial and aquatic habitat on common toads. Based on my findings, I consider the impacts of habitat at local, landscape and national scales. My research revealed the importance of pond density and presence of woodland in increasing relative probability of toad occurrence in the terrestrial habitat (Chapters 2 and 3) and the importance of water quality, woodland coverage and available terrestrial habitat coverage in determining common toad presence in ponds. The isolating effect of urban areas is demonstrated in Chapter 4 where Isolation By Barriers (IBB) explains genetic distance between common toad breeding populations better than Isolation By Distance (IBD). In Chapter 5 I again use the resource selection function for terrestrial habitat use developed in Chapter 3, to investigate the importance of terrestrial habitat availability in determining pond use by common toads at a national scale. In my concluding chapter, I make recommendations for management and further research including consideration of potential interactions between the effect of habitat loss, fragmentation and degradation with other potential causes of common toad decline.

1. Insect pollinators have been shown to alter their foraging patterns in response to habitat and landscape composition, particularly in relation to changes in the availability of floral resources which provide essential pollen and nectar provisions. Changes to pollinator behaviour and community composition, may alter the distance, directness and frequency of pollen movement and thus, the compatibility and genetic relatedness of pollen transferred between plants. We still lack good understanding of how variation in the spatial and temporal availability of floral resources drives pollinator responses and in turn, affects the fitness of outcrossing plants. Knowledge in this area could contribute to improved management interventions to enhance pollination services for plant conservation. 2. Through a combination of habitat and landscape scale field experiments, I explored how the availability of floral resources at different spatial scales affected plant-pollinator interactions, pollen transfer and mating success in plant populations, particularly those isolated from conspecifics. This involved introducing different species of plants in experimental arrays across a range of study systems that varied in structure and floral availability. Over the course of the thesis, I measured the community composition and behaviour of pollinators visiting experimental arrays; focusing on traits considered important for pollen transfer (e.g. Inter-tegular ('IT') span). Pollen movement was quantified within and between populations (5-150m) and the resulting plant outcrossing rates were measured using different methods including paternity analysis and the use of a dominance inheritance system. In addition, the implications of variations in pollinator foraging and pollination services can be attributed to pollen and gene flow and subsequently the reproduction and fitness of plants were assessed as a means of predicting the impacts on longer-term plant survival. 3. Findings from this thesis demonstrate reductions in the activity density (the abundance of actively foraging pollinators) and richness of pollinators and thus, the potential for plant visitation in response to a high abundance of floral resources within a habitat. This led to disruptions in pollen transfer, illustrated through a lower incidence of intra and inter-population pollen movement, and ultimately, reduced plant outcrossing rates. In parallel, plant seed set and germination rates were also reduced in habitats with high resource availability. Changes to pollinator communities and pollination services varied with the spatial scale at which floral resources were measured. Pollinator communities (activity density, richness and IT span) were most affected by floral resource abundance at a local scale (1-50m), particularly within a 20m radius of a plant population. Intra-population pollen movement was similarly affected by floral resources at a local spatial scale (within a 1m radius of a plant population). In contrast, no effect was observed on pollinator communities, intra-population pollen movement or plant reproduction when floral resources were measured at a landscape scale (within a 100-1500m radius of a plant population). However, findings were variable across different experiments at the same scale of measurement. For instance, the availability of floral resources at a local scale did not always elicit an effect on plant reproduction. This reflects differences in plant species identity and the effects of breeding system and floral traits, illustrated through variations in visitation rates between plant species. Inconsistencies were further observed with pollinator activity density and richness, which were not related to floral resources at a habitat scale in one chapter. 4. This thesis highlights the importance of the availability of floral resources at a local scale on plant-pollinator interactions and pollination services to plants. Co-flowering plants within florally rich habitats compete for pollinators and subsequently, visitation and pollen transfer between individuals of low density plant populations is diluted rather than facilitated. This suggests that although pollinator abundance and diversity may be enhanced through florally rich habitats (e.g. habitats implemented under the agri-environment scheme), pollination services are not automatically improved for plants which are present at low frequency in the landscape. This needs to be considered when designing and implementing management for threatened or isolated plants where plants may instead benefit from focused interventions. For instance, pollination services may be increased by efforts to maximise the facilitative effect of surrounding habitats, while increasing the ability of threatened or isolated plants to withstand competition from co-flowering plants.

Many bat species in Europe have undergone severe population declines during the last century and one of the driving causes is believed to be the loss of roosting and foraging habitat through agricultural expansion and intensification. Modern agricultural practices have also had strong negative effects on many insect groups, such as moths, which are important components of the diets of many bat species. Agri-environment schemes (AES) have been introduced in many countries as an attempt to counteract the negative effects of intensive agriculture on biodiversity by providing financial incentives for farmers to adopt environmentally-sensitive agricultural practices. AES are potentially beneficial to bats and nocturnal insects, but the response of these taxa to their implementation had not been assessed prior to this study. Here, the potential benefits (or otherwise) that bats and their insect prey species gain from the implementation of certain AES management prescriptions was assessed using ultrasonic detectors (to assess bat activity levels) and heath light traps (to quantify nocturnal insect abundance) at 18 pairs of AES and conventionally-managed farms. In addition, the influence of the surrounding landscape on bats and insects was quantified to evaluate the relevance of a landscape-scale management approach for the conservation of these taxa. Some of the AES prescriptions assessed in this study benefited moths (and are potentially beneficial for moth-eating bats), but not Pipistrelle bats nor their insect prey. The most important factors associated with bat activity on farmland were metrics related to woodland configuration in the surrounding landscape, which suggests that conservation efforts for bats should focus on the creation and management of this habitat. Currently, some AES prescriptions aim to increase the amount and quality of woodland on agricultural land, but little is known about how woodland character relates to bat abundance and insect prey availability; therefore, recommendations for woodland creation and management rarely consider the requirements of foraging bats. Here, the influence of woodland character (e.g. vegetation structure and patch configuration) on bats and nocturnal insects was assessed. Vegetation surveys were conducted and Geographic Information Systems (GIS) were used to quantify the vegetation character and spatial configuration of 34 woodland patches within farmland. Two complementary methods (acoustic monitoring and bat trapping assisted by an acoustic lure) were used to assess the influence of woodland vegetation character, patch configuration and the surrounding landscape on bat populations. Nocturnal insect abundance at each site was assessed using heath light traps. Data presented here demonstrate that bats show species-specific associations with woodland vegetation structure and patch configuration; patterns of higher bat abundance and activity at small and isolated woodland patches suggest that bats utilize this habitat more intensively in landscapes where woodland is scarce. This thesis also shows that moths are strongly influenced by woodland character; in general, large woodland patches of compact shapes, composed of a large number of native tree species and a dense understory cover, and located close to other woodlands were associated with high moth abundance and species richness (and are potentially valuable for moth-eating bats). Other nocturnal insects (mainly Diptera) were not influenced by woodland character. This study also shows that bats and nocturnal insects are influenced by the landscape context; moths are mainly influenced by the extent of semi-natural environment (such as rough grassland and scrub) within small spatial scales (within 250 m; although effects of woodland extent were detected at larger spatial scales for woodland specialists moths). Bats are mainly influenced by woodland-related landscape metrics. Some bat species are influenced by the surrounding landscape at large spatial scales (within 3 km) and would benefit from woodland creation and management at a wide-landscape-scale. The findings presented in this thesis have important management implications for the design of agri-environment schemes. A list of management recommendations to optimize the benefits that bats and nocturnal insects gain from these schemes is presented in the final section.

Halbnatürliche Grünlandflächen sind artenreiche Habitate von großer Bedeutung für viele Tier- und Pflanzenarten und die Bereitstellung zahlreicher Ökosystemdienstleistungen. Jedoch werden diese Flächen zunehmend seltener, weshalb ihr Schutz in Europa ein wichtiges Ziel geworden ist. Der Verlust von halbnatürlichem Grünland ist häufig mit einer Intensivierung der Agrarwirtschaft verbunden und innerhalb Europas geographisch sehr unterschiedlich. Diese Arbeit befasst sich hauptsächlich mit der Region Südtranssilvanien in Rumänien, in der fast alle dauerhaften Grünlandflächen halbnatürlich sind, jedoch von der zunehmenden Intensivierung bedroht werden. Der Schutz dieser Grünlandflächen wird hier auf unterschiedlichen räumlichen Ebenen und aus unterschiedlichen Blickwinkeln betrachtet, um sowohl die ökologischen als auch die gesellschaftlichen Aspekte der Bewirtschaftung zu berücksichtigen. Schutzmaßnahmen werden derzeit hauptsächlich auf der Feldebene umgesetzt, jedoch interagieren Grünlandarten häufig auch mit Populationen in der umgebenden Landschaft. Daher beschäftigt sich Kapitel 2 dieser Arbeit am Beispiel von Pflanzen und Heuschrecken mit den Auswirkungen von ökologischen Prozessen auf Grünlandarten auf lokaler und auf Landschaftsebene. Die Ergebnisse zeigen, dass die Landschaftszusammensetzung im 2 km-Radius einen gleichstarken Effekt auf die Artenvielfalt hat wie die lokalen Faktoren. Hierbei steigt der Pflanzenartenreichtum mit höherer Landschaftsheterogenität, während die Heuschrecken positiv auf den Anteil von Grünlandfläche in der Umgebung reagieren. Schutzmaßnahmen für artenreiches Grünland sollten daher Prozesse auf Landschaftsebene mit berücksichtigen, obwohl kein Landschaftstyp gleichzeitig alle Artengruppen begünstigt. Daher ist die Förderung einer extensiven Landwirtschaft die beste Möglichkeit, eine Vielfalt an Landschaftstypen zu erhalten, die die Artenvielfalt der Grünländer unterstützt. Neben dem Design von Schutzmaßnahmen ist auch ihre Umsetzbarkeit von großer Bedeutung. In der Untersuchungsregion ist die Kooperation der Nutzer miteinander besonders wichtig für Management-Entscheidungen, da es sich bei dem beweideten Grünland überwiegend um gemeinschaftlich benutzte Flächen (Allmendweiden) handelt. Allerdings zeigt Kapitel 3, dass sich dieses System hin zur Aufteilung der Flächen in kleinere Parzellen, die von Einzelnen gepachtet werden, verändert. Diese „Privatisierung“ der Allmende wird hauptsächlich von den flächenbasierten Zahlungen der gemeinsamen EU-Agrarpolitik gefördert. Sie wirkt sich derzeit sowohl negativ auf den Zugang von Kleinbauern zur Weide, als auch möglicherweise auf deren extensive Bewirtschaftung aus. Kapitel 4 untersucht daher das Potential von Bauernverbänden für die Wahrung der gemeinschaftlichen Bewirtschaftung von Allmendweiden. Bauernverbände können mithilfe von Agrarsubventionen eine extensive Bewirtschaftung der Allmendweide sichern sowie auch Informationen und Dienstleistungen für die Landwirte bereitstellen. Derzeit bedürfen derartige Verbände in der Untersuchungsregion allerdings noch Unterstützung bei der Organisation ihrer Aktivitäten. Forschung und Politik auf der europäischen Ebene müssen die Vielfalt der sozio-ökologischen Kontexte berücksichtigen, unter denen Naturschutz in Agrarlandlandschaften stattfindet. Kapitel 5 zeigt auf, dass die Unterschiede im Naturschutz in der Agrarlandschaft zwischen Ländern in West- und Osteuropa nicht ausreichend wahrgenommen werden. Forschung und Politik sind vorwiegend auf westeuropäische Länder fokussiert, während sich besonders große Flächen von artenreichen Agrarlandschaften jedoch in Osteuropa befinden. Diese benötigen häufig andere Naturschutzkonzepte, da sich die Hofstruktur und die Einstellung gegenüber dem Naturschutz vielfach von der in Westeuropa unterscheiden. Forschung in weniger untersuchten Gegenden sollte gefördert werden, um regional-spezifische, wissensbasierte Maßnahmen zu erarbeiten. Zudem sollte versucht werden, über Umweltbildung die Effektivität von Maßnahmen zu erhöhen. Die ausgedehnten Grünlandflächen in Südtranssilvanien bieten eine hervorragende Möglichkeit extensive, artenreiche Agrarlandschaften zu untersuchen und zu schützen. Auch wenn die Bewirtschaftung traditionell wirkt, ist der Fortschritt in vielen Bereichen sichtbar. Diese von Menschen geschaffenen Habitate müssen den zukünftigen Bedürfnissen einer wachsenden Bevölkerung angepasst werden. Diese Arbeit versucht durch das Verständnis der Einflussfaktoren auf Grünland, Wege aufzuzeigen, wie Entwicklungs- und Naturschutzziele miteinander verbunden werden können. Dies kann vor allem durch wissensbasierte und effiziente Naturschutzmaßnahmen und durch die Stärkung der Zusammenarbeit unterschiedlicher Interessengruppen erreicht werden. Dies gilt für viele Teile Osteuropas, in denen extensive Landwirtschaft und gemeinschaftliche Landnutzung Möglichkeiten bieten, artenreiche Agrarlandschaften auch in Zukunft zu erhalten.

During the past several decades, agricultural intensification has been crucial to increase the food supply. Several processes related to intensification are very detrimental to the environment, particularly biodiversity. Today, agriculture is facing the challenge of satisfying its demand for food while improving its environmental sustainability. Knowledge of the shape of the relationship between biodiversity and intensity is necessary to determine both where conservation policies will be most effective and how to allocate intensity to reconcile production and biodiversity. Few empirical studies on this relationship exist, and the influence of the spatial arrangement of intensity on biodiversity remains untested. This Ph.D. thesis determined how to target both agricultural intensity and its spatial allocation for meeting production and conservation objectives of farmlands. To answer this research question, we used a country-scaled approach that combined two France-scaled databases that describe agriculture and farmland birds. We characterized a nationwide gradient of agricultural intensity and studied a farmland bird community along this gradient, using several trait-based descriptors (specialization, trophic level, and species main habitat). Agricultural intensity and bird communities were described at the Small Agricultural Region (SAR; mean width = 22.4 km) level. As a first step, we developed a novel method to estimate an intensity indicator that was based on Input Costs/ha, with SAR resolution. This indicator provides a continuous intensity measure that is relevant across different types of agricultural systems. Secondly, we investigated the effects of a gradient of land uses (grassland to arable land) and its heterogeneity on the bird community. We found habitat specialists suffered from habitat loss, while generalists benefited from heterogeneity. Thirdly, we showed that the community responded significantly to intensity, with winner species replacing loser species along the gradient. The shift between losers and winners was sharper at low intensities. Interestingly, spatial aggregation of intensity had a strengthening effect on the bird community. Finally, the relationships linking intensity to the bird community, food production, and economic performance were integrated into a model aimed at optimizing intensity allocation. Optimal allocations reached win-no-lose solutions with the three criteria. They corresponded to targeted intensity modifications: many small changed, favoring homogeneous, extensive clusters, were optimal within an extensification scenario; while a few large changes, favoring heterogeneity, were optimal within an intensification scenario. We provide one of the first studies demonstrating that spatial aggregation of intensity can influence the biodiversity/intensity relationship. Our results also provide an opportunity to improve the effectiveness of conservation policies, at national scales, with spatial targeting: opposite targeting should be performed either to maximize biodiversity benefits or to increase production, while mitigating biodiversity impacts. Our results highlight the importance of mixed allocation strategies between land sparing/sharing extremes. In order to put these opportunities into effect, further research should address the technical solutions that achieve intensity modification at the farm level and design targeted policies that benefit biodiversity and other environmental criteria

Theoretical part of the diploma thesis (review) is focused on historical development of the Common Agricultural Policy (reforms from the years 1999 and 2003 are emphasized) and on the comparison of the agri-environment schemes (AES) of the Czech Republic, Slovak Republic, and Austria. The aim of the review was to summarize the processes, which led to the recent form of AES. In practical part of the thesis measures, which support maintaining and increasing of populations of ground game and birdlife, i.e. measures Catch Crops, Rich Seed Habitat (Biobelt), and Bird Area on Grasslands were evaluated. Data from Paying Agency SZIF were used. The study covers both, the (shortened) programming period 2004-2006 and the programming period 2007 {--} 2013 (years 2004 {--} 2008). Thesis is focused on region NUTS II Southeast. The following indicators were analysed: interest of the farmers in the selected AES measures, area on which the measures were carried out and amount of the financial support spent to support individual measures. Finally, steps to optimize the use of financial resources are suggested. Catch Crops are used as a measure on arable land. The highest interest of the farmers in Catch Crops was observed in the year 2004, when the largest number of the farmers entered this measure. The interest was decreasing in the following years (especially in the years 2007 and 2008, when the endowment was lowered). Catch Crops cover 6 {--} 8 % of the arable land of the region and the area has been increasing in time. Biobelt is only sporadically used measure (probably because of the underestimation of the costs), but interest in it (albeit low) has been increasing during the whole period. Measure Bird Area on Grasslands is restricted to nesting areas of Corncrake (Crex crex) and Waders (Charadrii). In NUTS III South Bohemian Region, the measure was applied on approximately 27 % of the area where it potentially can be used during the whole observed period. In NUTS III Plzeň Region, the area increased from 26% in the years 2004 {--} 2006 to 60 % in the years 2007 and 2008.

Im Rahmen der Gemeinsamen Agrarpolitik der Europäischen Union wurden Agrarumweltprogramme (AES) entwickelt, um die durch die Landwirtschaft verursachte Zerstörung der natürlichen Umwelt zu bekämpfen. Um die ökologische Wirksamkeit der Systeme zu verbessern, wird ein kollektiver Ansatz empfohlen, der sich auf eine Landschaft statt auf eine einzelne Betriebsebene konzentriert. Dieser Ansatz wird in ganz Europa selten angewendet, außer in den Niederlanden, wo seit 2016 alle AES gemeinsam realisiert werden müssen. Da die Teilnahme an den Programmen freiwillig ist, ist es von entscheidender Bedeutung, die Motivation der Landwirte zu verstehen, sich anzuschließen, da die Annahme und Umsetzung von Maßnahmen eine Voraussetzung für die Erreichung ist irgendwelche Effekte. Ziel dieser Studie ist es daher, die Motivation niederländischer Landwirte zur Teilnahme an kollektiven AES zu untersuchen und die wichtigsten Vor- und Nachteile des Programms herauszufinden, die von den Landwirten wahrgenommen werden. Eine Q-Studie mit 15 Landwirten aus sechs Provinzen zeigt drei vorherrschende Motivationsansichten: eine kollektivorientierte, eine wirtschaftsorientierte und eine umweltorientierte Perspektive. Alle Bauern eint ihre Zuneigung und Sorge für die Natur, die von unterschiedlichem Problembewusstsein und Kollektivzugehörigkeit begleitet wird. Finanzieller Ausgleich wird von allen als wichtig erachtet, jedoch eher als notwendiges Mittel, um notwendige Änderungen in der landwirtschaftlichen Praxis zu ermöglichen, denn als zusätzliche Einnahmequelle. Während die niederländischen Regelungen noch weiter verbessert werden können, um mehr Flexibilität, eine bessere Integration des Wissens der Landwirte und eine bessere Kommunikation zu ermöglichen, weisen alle Landwirte viele Vorbehalte im Zusammenhang mit kollektiven Maßnahmen zurück, was darauf hindeutet, dass der niederländische Ansatz über die nationalen Grenzen hinaus gefördert werden könnte. / Within the European Union’s Common Agricultural Policy, agri-environment schemes (AES) have been designed to address the degradation of the natural environment caused by agriculture. To improve the schemes’ ecological effectiveness, a collective approach focusing on a landscape instead of a single farm level is recommended. This approach is rarely applied across Europe except for the Netherlands, where all AES have to be realised collectively since 2016. As participation in the schemes is voluntary, understanding farmers’ motivation to join is crucial since the uptake and implementation of measures is prerequisite for achieving any effects. Hence, the aim of this study is to explore Dutch farmers’ motivation to participate in collective AES and to find out about the scheme’s main advantages and disadvantages perceived by the farmers. A Q study with 15 farmers from six provinces shows three dominant motivational views: a collective-oriented, a business-oriented and an environment-oriented perspective. All farmers unites their affection and care for nature, which is accompanied by different levels of problem awareness and affiliation to the collective. Financial compensation is deemed important by all, yet rather as necessary mean to enable required changes in farming practices than as additional source of revenue. While the Dutch schemes can still be further improved to allow for more flexibility, a better integration of the farmers’ knowledge and enhanced communication, all farmers dismiss many caveats related to collective action, indicating a potential to promote the Dutch approach beyond national borders.

No description available.

L'intensification de l'agriculture a joué un rôle crucial pour augmenter la production alimentaire au cours des dernières décennies. Plusieurs processus liés à l'intensification ont aussi causé d'importants dommages environnementaux, sur la biodiversité en particulier. L'agriculture doit aujourd'hui faire face au défi de satisfaire à une demande alimentaire croissante tout en améliorant son impact environnemental et sa durabilité. Il est nécessaire de connaître la forme de la relation entre biodiversité et intensité agricole pour déterminer où les politiques de conservation seront les plus efficaces et quelles allocations spatiales de l'intensité permettront de concilier production et biodiversité. Il existe peu de preuves empiriques de la forme de cette relation, de plus, l'influence de l'arrangement spatial de l'intensité sur la biodiversité demeure inconnue. Cette thèse avait pour objectif de déterminer comment cibler l'intensité agricole et son allocation spatiale afin d'atteindre des objectifs à la fois productifs et environnementaux. Afin de répondre à cette question, nous avons adopté une approche à l'échelle de la France entière, en couplant des bases de données décrivant l'agriculture et des oiseaux spécialistes des milieux agricoles à cette échelle. Nous avons caractérisé un gradient d'intensité à l'échelle du pays et étudié une communauté d'oiseaux spécialistes des milieux agricoles tout au long de ce gradient. Plusieurs descripteurs de cette communauté ont été utilisés, renseignant sa taille (richesse spécifique) mais aussi sa composition (spécialisation, niveau trophique, habitat). L'intensité agricole et les communautés d'oiseaux ont été reliées au niveau de la Petite Région Agricole (PRA; largeur moyenne = 22.4 km). Tout d'abord, nous avons développé une méthode permettant d'estimer un indicateur d'intensité agricole basé sur le coût intrant par hectare, au niveau de la PRA. Cet indicateur fournit une valeur d'intensité continue, pertinente à la fois pour les systèmes d'élevage et de culture. Ensuite, nous avons examiné les effets d'un gradient d'utilisation des sols (des prairies aux grandes cultures) et de leur hétérogénéité, sur la communauté d'oiseaux. L'hétérogénéité a un effet négatif sur les espèces spécialistes car elle entraine la perte de leur habitat. En revanche, elle avantage les espèces généralistes. Lors d'une troisième étape, nous avons montré que la communauté d'oiseaux était significativement influencée par l'intensité. Le long du gradient des espèces « gagnantes » remplacent des espèces « perdantes », ce changement étant plus marqué aux faibles intensités. L'effet de l'intensité sur la communauté d'oiseaux est renforcé par son agrégation spatiale. Enfin, les relations entre l'intensité, la communauté d'oiseaux, et les performances productives et économiques ont été intégrées dans un modèle d'optimisation de l'allocation de l'intensité. Les allocations optimales révèlent des solutions gagnant-non-perdant entre les trois critères de performance (biodiversité, production et économie). Ces allocations optimales correspondent à des modifications d'intensité ciblées: beaucoup de petits changements, favorisant des zones homogènes et extensives dans le cas d'un scénario d'extensification, à l'opposé de changements importants et moins nombreux, favorisant plus d'hétérogénéité, dans le cas d'un scénario d'intensification. Cette thèse apporte une des premières démonstrations de l'influence de l'agrégation spatiale de l'intensité sur la relation entre biodiversité et intensité. Nos résultats révèlent une opportunité pour améliorer l'efficacité des politiques de conservation de la biodiversité à l'échelle nationale. Il s'agit d'un ciblage de ces politiques, qui devra être différent pour maximiser la biodiversité à coût productif réduit ou pour augmenter la production tout en limitant les dommages sur la biodiversité / During the past several decades, agricultural intensification has been crucial to increase the food supply. Several processes related to intensification are very detrimental to the environment, particularly biodiversity. Today, agriculture is facing the challenge of satisfying its demand for food while improving its environmental sustainability. Knowledge of the shape of the relationship between biodiversity and intensity is necessary to determine both where conservation policies will be most effective and how to allocate intensity to reconcile production and biodiversity. Few empirical studies on this relationship exist, and the influence of the spatial arrangement of intensity on biodiversity remains untested. This Ph.D. thesis determined how to target both agricultural intensity and its spatial allocation for meeting production and conservation objectives of farmlands. To answer this research question, we used a country-scaled approach that combined two France-scaled databases that describe agriculture and farmland birds. We characterized a nationwide gradient of agricultural intensity and studied a farmland bird community along this gradient, using several trait-based descriptors (specialization, trophic level, and species main habitat). Agricultural intensity and bird communities were described at the Small Agricultural Region (SAR; mean width = 22.4 km) level. As a first step, we developed a novel method to estimate an intensity indicator that was based on Input Costs/ha, with SAR resolution. This indicator provides a continuous intensity measure that is relevant across different types of agricultural systems. Secondly, we investigated the effects of a gradient of land uses (grassland to arable land) and its heterogeneity on the bird community. We found habitat specialists suffered from habitat loss, while generalists benefited from heterogeneity. Thirdly, we showed that the community responded significantly to intensity, with winner species replacing loser species along the gradient. The shift between losers and winners was sharper at low intensities. Interestingly, spatial aggregation of intensity had a strengthening effect on the bird community. Finally, the relationships linking intensity to the bird community, food production, and economic performance were integrated into a model aimed at optimizing intensity allocation. Optimal allocations reached win-no-lose solutions with the three criteria. They corresponded to targeted intensity modifications: many small changed, favoring homogeneous, extensive clusters, were optimal within an extensification scenario; while a few large changes, favoring heterogeneity, were optimal within an intensification scenario. We provide one of the first studies demonstrating that spatial aggregation of intensity can influence the biodiversity/intensity relationship. Our results also provide an opportunity to improve the effectiveness of conservation policies, at national scales, with spatial targeting: opposite targeting should be performed either to maximize biodiversity benefits or to increase production, while mitigating biodiversity impacts. Our results highlight the importance of mixed allocation strategies between land sparing/sharing extremes. In order to put these opportunities into effect, further research should address the technical solutions that achieve intensity modification at the farm level and design targeted policies that benefit biodiversity and other environmental criteria