Interactive effects of landscape context constrain the effectiveness of local agri-environmental management.
Ecological theory predicts that the effectiveness of local agri-environmental management to enhance species richness at field scales will be the highest at intermediate levels of landscape complexity because of nonlinear effects of landscape context on field-scale diversity. We examined how landscape complexity determined effectiveness of local agri-environmental management in terms of effects on species richness of birds, plants, spiders and bees in 232 extensive and intensive paired fields (112 arable fields and 120 grasslands) from 18 regions located in six European countries. As predicted, landscape complexity enhanced field-scale species richness in a mostly nonlinear (sigmoidal) way, with earlier species richness increases in extensive than in intensive fields along landscape complexity gradients. Length of semi-natural boundaries (for arable fields) and proportion of unfarmed habitat (for grasslands) were the landscape features influencing species richness. The relationships between effectiveness of local management and landscape complexity for all taxa were best described with hump-shaped curves, indicating the highest effectiveness at intermediate landscape complexities. Synthesis and applications. We used models to investigate how and why effects of local management intensity on species richness vary along wide gradients of landscape complexity. We conclude that landscape-scale management options should take priority over local extensification measures within agri-environmental programmes. These programmes should follow a hierarchical multi-scale approach directed to address landscape-scale constraints on local diversity.