Climate and land use changes are both key factors affecting biodiversity. Moreover, the need to reconcile agricultural production and biodiversity, by improving existing conservation measures and by integrating environmental considerations into future agricultural policies, has become a major concern. The aim of the thesis was to study how environmental changes (climate and agricultural land use) and conservation measures implemented in response to these environmental pressures, may affect breeding bird communities. The first part of my work focused on assessing the effects of agri-environment schemes (AES) recently implemented in France. The results demonstrated overall mixed effectiveness of AES, although some of them seem to have the potential to improve the dynamics of declining populations. In the second part, I tried to predict the potential impacts of changes in future environments on bird communities. Predictions of potential impacts of different CAP scenarios by 2020 highlighted the need to develop scenarios at fine spatial scale, taking into account the diversity of agroecosystems in France. Thus, I developed different scenarios of changes in cropping patterns across French small agricultural regions, some of which developed at two different scales of policy-making: national and regional. Predicted impacts of these scenarios combined with various scenarios of climate and land use changes, proved especially that regionalization of extensification policies according to agroecosystems could help to maximize the conservation of common bird communities in agricultural landscapes. In conclusion, the development of such predictive approaches is useful for estimating the environmental impacts of potential changes in climate and land use, and is therefore a real tool for decision support to participate in the development of policies
