Conservation of grassland patches failed to enhance colonization of ground-active beetles on formerly cultivated plots

The dry grasslands of the Mediterranean Basin have been traditionally managed since ancient times, but have been drastically degraded by recent human activities such as cultivation. Cultivated plots in a dry grassland of Southern France were abandoned more than 20 years ago, but their vegetation and ground-active beetle community structure and composition differ considerably from neighbouring uncultivated grassland plots. Because these formerly cultivated plots are adjacent to an uncultivated grassland area, they constitute a model system for examining beetle recolonization patterns on field margins. No edge effect or ecotone was identified on the margins between two of the formerly cultivated plots and the uncultivated dry grassland; there was no significant peak of beetles species richness in this area. All the most common dry grassland beetle species (mainly saprophagous and predatory species, which are less habitat-specialist than phytophagous species) had already recolonized the formerly cultivated plots. However, although uncultivated dry grassland was adjacent to the formerly cultivated plots it was insufficient for complete regeneration of dry grassland beetle communities on formerly cultivated plots, indicating habitat quality remained lower even after 20 years. Understanding the causes of spatial variation in active-ground beetles at the species level is important before the ecological restoration of habitat quality to its prior state, using the adjacent steppe as a reference.