Multi-scale trade-offs between production and environment in grassland agroecosystems: application to livestock farming systems and biodiversity conservation

In European grasslands, grazing and mowing regimes are major drivers of the maintenance of many wild species, either through direct or indirect effects. To date, both types of effects were studied separately, mainly at the field scale and with no quantification of performance. Objective of this study was to model the trade-offs between ecological and productive performance of a grassland agro-ecosystem at two nested scales i.e. field and farm scales. We developed a dynamic model linking grass dynamics controlled by grazing or mowing to stochastic population dynamics of two grassland bird species. Bird dynamics were driven by both direct and indirect effects of management. Viable control framework was used to predict productive and ecological performance. At field scale, results showed that the best ecological performance was obtained at intermediate levels of productive performance (60 to 108 grazing days /ha /year). Above 108 grazing days, no grazing strategy was viable for either species due to the negative direct effects of management. Between 108 and 240 grazing days, the ecological-productive relationship showed a concave Pareto like frontier. Any improvement in productive performance entailed a strong decrease in ecological performance. As expected, at farm scale the best ecological performance was obtained with extensive farms. However, the ecological-productive relationship showed a convex Pareto like frontier indicating the occurrence of compensations among management regimes. In intensive farms, it was necessary to allocate 40% of farm area in low-intensity grazing in order to compensate for the negative effects of mowing and high-intensity grazing on birds. However this land allocation involved a 25% reduction in productive performance. Finally, we explore several forms of complementarities among farm types to improve overall performance.