- Fallow agricultural land provides habitat for threatened and declining farmland biodiversity. Policy change under the EU's Common Agricultural Policy (CAP) has been driving the area of fallows over the past decades. It is still unclear, whether positive relationships between farmland biodiversity and fallow area are general in time and space, and what landscape factors moderate them at large scales.
- We analysed associations between fallow area and species richness and abundance of 24 farmland birds in 3 years covering three CAP funding periods, by linking agricultural statistics at the district level to plot-level bird data from a national-scale monitoring scheme. We tested whether these relationships are moderated by species' habitat preferences and landscape configurational complexity, measured as the edge density of woody features.
- Species richness was positively associated with fallow area in all three funding periods. We found a hump-shaped response along a gradient of increasing landscape configurational complexity. The associations between fallow area and species richness peaked at intermediate values of edge density.
- The associations between species abundance and fallow area varied among species, but there was strong support for positive and consistent associations in 15 (63%) of the studied species. There was little support for a moderating effect of landscape configurational complexity on the associations of fallow area and bird abundance.
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Policy implications. To support farmland biodiversity, we suggest promoting fallow land across all agricultural landscapes and anchoring respective ambitious targets in the CAP strategic plans. An increase of fallow land beyond minimum requirements through voluntary measures, such as eco-schemes and agri-environment schemes, should particularly target landscapes with intermediate configurational complexity.
