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1 December 2005 Effects of Forest Roads on Spatial Distribution of Boreal Carabid Beetles (Coleoptera: Carabidae)
Matti J. Koivula
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The total network of Finnish forest roads has increased from a few hundred km in 1950 to currently over 120,000 km, but the ecological consequences of that process on invertebrates are poorly understood. I pitfall-trapped carabid beetles (Coleoptera: Carabidae) at roadsides and in adjacent forests along six forest roads in Finland. I carried out two studies on whether roads function as obstacles to the movement of forest carabids, or dispersal corridors for generalist and open-habitat species. In addition to these two studies, I compiled carabid observations from national entomologists to get an overview on carabid richness and on life-history traits associated with roadside carabids. A forest carabid Calathus micropterus (Duftschmid) was less abundant on the roadsides, compared to the adjacent forests. However, species richness and the abundance of a habitat generalist Pterostichus niger (Schaller) showed the opposite, and open-habitat species were solely caught on the roadsides. At the roadsides, generalists decreased in abundance with increasing distance to the nearest large open-habitat area along the road. This result may indicate that roadsides are dispersal corridors and/or “sink” habitat for these carabids. I did not detect such a trend for open-habitat species, which may indicate that roadsides are habitats, not just dispersal corridors for these carabids. Multivariate Regression Trees showed that the roadside and forest carabid assemblages were different. Forest type played a key role in shaping carabid assemblages of forests, whereas roadside carabid assemblages were mostly affected by factors related to lighting conditions (road width, proximity of open habitat, and compass direction). I caught several forest carabids between the ruts of forest roads, indicating that these beetles frequently cross forest roads. The 97 carabid species found by Finnish entomologists from different kinds of roadsides, reported here, indicate that roadsides host rich carabid assemblages of relatively common species mostly associated with open and man-made habitats.

Matti J. Koivula "Effects of Forest Roads on Spatial Distribution of Boreal Carabid Beetles (Coleoptera: Carabidae)," The Coleopterists Bulletin 59(4), 465-487, (1 December 2005).
Received: 3 February 2005; Accepted: 1 May 2005; Published: 1 December 2005

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