Time-lagged response of carabid species richness and composition to past management practices and landscape context of semi-natural field margins.

Field margins are key features for the maintenance of biodiversity and associated ecosystem services in agricultural landscapes. Little is known about the effects of management practices of old semi-natural field margins, and their historical dimension regarding past management practices and landscape context is rarely considered. In this paper, the relative influence of recent and past management practices and landscape context (during the last five years) were assessed on the local biodiversity (species richness and composition) of carabid assemblages of field margins in agricultural landscapes of northwestern France. The results showed that recent patterns of carabid species richness and composition were best explained by management practices and landscape context measured four or five years ago. It suggests the existence of a time lag in the response of carabid assemblages to past environmental conditions of field margins. The relative contribution of past management practices and past landscape context varied depending on the spatial scale at which landscape context was taken into account. Carabid species richness was higher in grazed or sprayed field margins probably due to increased heterogeneity in habitat conditions. Field margins surrounded by grasslands and crops harbored species associated with open habitats whilst forest species dominated field margins surrounded by woodland. Landscape effect was higher at fine spatial scale, within 50 m around field margins. The present study highlights the importance of considering time-lagged responses of biodiversity when managing environment. It also suggests that old semi-natural field margins should not be considered as undisturbed habitats but more as management units being part of farming activities in agricultural landscapes, as for arable fields.