The influence of riparian buffer strips on carabid beetle (Coleoptera, Carabidae) assemblage structure and diversity in intensively managed grassland fields

Abstract

The use of riparian buffer strips as a means of reducing diffuse pollution in European grassland systems is becoming more common and consequently there is a need for comprehensive research on the influence of buffer strip management, placement and structure on biodiversity. Carabid assemblages were examined in a range of riparian zones in intensively managed grassland in Scotland. Carabids were monitored by pitfall trapping in riparian zones open to grazing, wide riparian buffer strips (>5 m wide), narrow boundary strips (<2 m wide) and adjacent fields in order to determine factors influencing carabid diversity and assemblage structure. While carabid diversity was greater in open riparian zones and narrow boundary strips when compared to the adjacent fields, it was actually poorer in wide riparian buffers when compared to open zones thus indicating wide buffers may actually be detrimental to carabid diversity. Carabid assemblages in wide riparian buffers were, however, more distinct from the adjacent field than narrow boundary strips or riparian zones open to grazing. Consequently, while the presence of wide riparian buffers may not promote carabid diversity within the actual buffer strips, by adding an additional habitat that supports a distinct carabid assemblage, riparian buffer strips may promote diversity at the landscape level. Carabid assemblage structure was driven by a combination of soil and vegetation characteristics in addition to physical attributes including distance from the watercourse and width of the strip. Only when we have a better understanding of the factors influencing biodiversity within riparian buffer strips can we start to formulate effective management prescriptions that fuse their dual function of pollution mitigation and biodiversity promotion.