Designing grassland landscapes for economic or ecological priorities: application to livestock farming and birds
Résumé
Grassland birds are facing increasing threats due to the intensification of agricultural practices. Grazing or mowing can have negative and positive effects on wader dynamics at field scale and land use distribution influences these dynamics at landscape scale. The aim of this study was to assess the ecological and economic performances of several agricultural landscapes composed by different farm types. Based on a database from the Marais Poitevin (France), farm types were characterised using several indicators of management intensity and were used to generate several hypothetical landscapes which were compared to the current landscape according to their ecological and economic performances. A stage structured stochastic model was developed to asses the long term effects of grazing and mowing practices on ground nesting birds on contrasted landscapes. A simplified version of the meta-population model made it possible to asses the importance of the mowing/grazing ratio on bird dynamics in a grassland landscape. Stocking rate per hectare of main fodder area proved itself to be a good indicator of farm management intensity and four farm types were identified. Landscapes comprising either large or small extensive farms were the most efficient on an ecological viewpoint but small extensive farms had on average the poorest economic performances. From these results it was inferred that landscapes made off large extensive farms were more likely to reconcile economic and ecological priorities. However, accounting for the social aspects of farming calls attention to the potential role of small extensive farms in sustainable management of grassland landscapes.