In recent decades, agricultural intensification and landscape simplification have dramatically affected farmland biodiversity. To reduce this trend, agri-environmental schemes (AES) of the Common Agricultural Policy (CAP) were launched in the European Union in the early 1990s. Since then an effort has been made to asses the effectiveness of these measures, but, in the Mediterranean region, where olive groves are among the predominant crops, the effectiveness of AESs to maintain farmland biodiversity remains poorly evaluated. In conventional olive farming, the only AES now in practice are the implementation of herbaceous, non-crop vegetation within crops (i.e. ground covers) aimed at preventing soil erosion, and the maintenance of hedges. These practices, when applied separately, can increase structural complexity, likely benefitting farmland biodiversity at different spatial scales; however, little is known about the potential synergistic effects when these measures are applied in combination in Mediterranean agroecosystems. This study assessed the combined effects of herbaceous ground cover and hedges on passerine communities of olive groves over a 4-yr period. Hedges, and to a lesser extent ground covers, efficiently increased the abundance and richness of passerine communities of olive groves, particularly that of insectivorous birds, but the effects of both measures were independent of each other. Hedges were particularly relevant to the richness and abundance of passerine communities, especially at distances up to 50 m. Therefore, we suggest that management should promote the creation of a hedge network embedded in the olive grove matrix, for example by promoting or maintaining hedgerows located between properties. This study underscores the important role of increasing structural complexity in Mediterranean perennial agroecosystems through the implementation of ground covers and maintaining hedges, to preserve farmland passerine communities, and encourages the use of these agri-environmental measures as a tool in landscape planning and conservation.
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Vol. 50 • No. 2