Different policy scenarios to promote various targets of biodiversity

Biodiversity loss in farmlands is widely documented, and agriculture intensification has been identified as a main driver of this decline. Numerous agri-environmental policies have been implemented to assess the negative impacts of agricultural intensification on biodiversity. However, most published studies focus on land-use scenarios, thus neglecting the economic dimension. We develop a bio-economic spatially explicit modelling across 620 small French agricultural areas, which couples a public decision maker under budgetary constraint, regional economic agents in a context of uncertainty and breeding bird dynamics. Using dynamic models, we analyse the direct impacts of several current economic scenarios of the Common Agriculture Policy on common bird communities through five ecological indicators, all related to breeding populations of birds in farmlands: the farmland bird index (FBI), a generalist bird index (GBI), the Shannon diversity index, a community specialization index (CSI) and a community trophic index (CTI). We consider these indicators to scan various functional traits of bird communities. Trends in the different indicators are significantly contrasted pending on economic policy scenarios. Scenarios promoting intensive crops lead to small but specialized communities with more granivorous species, hence a low trophic level for the community. By contrast, promoting extensive grasslands increases the population size, enhances high trophic level but decreases community specialization. Evaluation of agricultural policies should not rely on a single indicator per taxonomic group. In the context of potential reversal of current bird declines, bio-economic modelling, involving farmland incomes, is proposed as a relevant support for decision making about sustainable agri-environmental policies. Promoting extensive grasslands is essential for the sustainable management of bird communities and agriculture. We, however, reveal more complex economic effects and synergies between public incentives, which appear to give interesting leverage for enhancing the bio-economic effectiveness of agricultural policies. (C) 2011 Elsevier Ltd. All rights reserved.