Temporal variability of connectivity in agricultural landscapes: do farming activities help?

In landscapes where natural habitats have been severely fragmented by intensive farming, survival of many species depends on connectivity among habitat patches. Spatio-temporal structure of agricultural landscapes depends on interactions between the physical environment and farming systems, within a socio-economic and historical background. The question is how incentives in agricultural policies may influence connectivity? May they be used to manage the land for biodiversity conservation? We used simulations based on property field maps to compare connectivity on the same landscape during seven years of crop succession for two dairy farming systems, one being representative of conventional systems of western France, the second one representative of systems undergoing intensification of production. Connectivity is a measure of landscape structure and species characteristics based on individual area requirements and dispersal distance. Models used are based on weighed distances, considering differential viscosity for different land uses. The results show that, for a given farming system, physical and field patterns constraints are such that landscape connectivity remains the same over years, while it is significantly different between the two farming systems. This is consistent with the recent input of policies to promote environmentally friendly farming systems, and confirms that policies must encounter the landscape level. The analysis also demonstrates that the localisation of forest patches, resulting from long term land cover changes, plays a central role in connectivity and overrides changes in agricultural land uses.