Seasonal variability in the response of ground beetles (Coleoptera: Carabidae) to a forest edge in a heterogeneous agricultural landscape in Japan

Abstract

Understanding arthropod responses to forest edges is essential to understanding both the characteristics of agro-ecosystems and the potential ecosystem services provided by forests adjacent to farmland in heterogeneous agricultural landscapes. Seasonal differ- ence in the responses of carabid beetles to forest edges was determined using transects that extended from the edge of the forest 22.5 m into the interior of a forest and 22.5 m into the meadow in three seasons, early summer, late summer and mid-autumn. The responses of carabids to the forest edge in terms of species richness and abundance differed significantly in the three seasons. The species richness and abundance peaked in the meadow 4.5 m from the edge and were low in the forest in summer, whereas they peaked at the edge and remained high in the forest in autumn. Species-level analyses revealed that several species did not move between habitats, indicating that the forest edge acted as a barrier for these species. Many species, however, peaked in the meadow near the edge and the distribu- tion of one species along the meadow-forest transect changed with the seasons. Our results indicate that secondary forests are not an effective sources of predators of pests, but do function as overwintering sites for some species. Because many species that prefer open land hibernate in field boundaries and fallow fields, the quality and spatial configuration of these habitats is important. Furthermore, in terms of pest management the seasonal dynamics of not only carabid beetles but other beneficial arthropods such as spiders and parasitoids should be considered.