Relative abundance and movement of the carabid beetle Scaphinotus angusticollis in managed coniferous riparian forests of southwestern British Columbia

Riparian reserves designed to protect stream ecosystems are valuable to the conservation of riparian obligate and forest-preferring species; however, there have been few studies of terrestrial invertebrates with more general habitat requirements. To characterize the use of riparian reserves by terrestrial insects, we examined the ecology of Scaphinotus angusticollis Mannerheim, a large and abundant carabid beetle with a broad distribution in coniferous forests of western North America. Population sizes and movement behaviour of S. angusticollis were contrasted among clearcuts, 30 m reserves, and unharvested riparian forests near Vancouver, British Columbia, Canada, with three sites per habitat type. The relative abundances of S. angusticollis were as high in 30 m reserve habitats as they were in unharvested forests, whereas populations in clearcuts were approximately half the size of those found in 30 m reserves. Beetle distributions relative to nearby streams were similar across habitat types. Beetles moved twice as far in 30 m reserves than in clearcuts, suggesting there are differences in this beetle’s perception of reserve habitat. This study provides evidence that 30 m riparian reserves offer habitat that maintains population sizes and facilitates movement of terrestrial insect species like S. angusticollis at levels similar to that of unharvested riparian forests.