Effects of soil tillage regime and frequency of cultivation on grassland bird assemblages in Mediterranean drylands

摘要

Conservation agriculture (CA) gained recently some visibility in the Mediterranean region. By affecting soil and plant ecology, CA is expected to influence other biological groups, notably farmland birds. This study aims to assess (1) the importance of tillage regime (conventional vs. no-tillage) and frequency of cultivation under these two regimes in determining the richness and abundance of birds in extensive grasslands originated within rotational cropping systems, and (2) how tillage systems contribute to changes in bird richness and abundance, comparatively to other drivers of bird ecology in Mediterranean farmland. We conducted bird censuses (point counts) from 2012 to 2016 in 34-52 fields per year of 15 farms in Evora region (Southern Portugal). Generalized Linear Mixed Models were used to link bird abundance/richness with agricultural descriptors. Both tillage regime and cultivation frequency showed weak effects on Species richness and Total bird abundance. However, a strong variability in the response to tillage descriptors was found between species. For the little bustard and the Iberian grey shrike, a strong interaction with the annual weather regime and opposite trends for the effect of tillage regime were detected. Despite its moderate influence on bird assemblages comparatively to other major drivers of bird richness and abundance (i.e. grazing and annual weather regime), CA could constitute a potential complementary "greening measure" to manage extensive grasslands within rotational cropping systems, particularly in areas where soil erosion is a problem, although some species may not benefit from its implementation.