Restoration of insect communities after land use change is shaped by plant diversity: a case study on carabid beetles (Carabidae)

There is no doubt about the insect decline currently taking place in ecosystems with large anthropogenic impacts. Thus, there is a need for practices that avoid insect decline and or help to recover insect communities that have already suffered. Plant diversity has been shown to be positively related to insect abundance and diversity and to ecosystem functions provided by insects. However, it remains open if increased plant diversity can help to recover decreased populations. Here, we tested over one decade the effects of plant diversity on the carabid community in a large grassland biodiversity experiment and how plant diversity fostered the establishment of a natural grassland community after conversion of an arable field. There was a dramatic decline in carabid abundance from 2003, the first year after establishing the diversity experiment, to 2005. However, subsequently, the abundance increased constantly. One year after the land use change most individuals and species were those commonly found in agricultural fields. In subsequent years the community was dominated by grassland species. While plant diversity did not affect the abundance and richness of the carabid community, the turnover to a more native grassland community was accelerated by plant diversity in the first years after the land use change. In contrast, in later years plant diversity stabilized the community assemblage. Our study shows that high plant diversity can contribute to a faster transition of insect populations towards naturally occurring community assemblages and at later stages to more stabilized assemblages.