Windstorm is the main natural disturbance in temperate forests. Canopy perforation induces important ecological changes in terms of microclimate and ground microhabitats and creates patchy open areas in the forest mosaic. In managed oak-hornbeam forests storm-damaged in France in 1999, we sampled carabid beetles by pitfall and window-flight interception traps in 2001. I compared ground beetle assemblages in unlogged natural openings vs closed forests. I studied short-term gap and gap size effects on carabid abundance, richness and assemblage composition (species and ecological groups based on habitat preference). Shortly after the disturbance, I observed a diversification of ground beetle assemblages in gaps at both air and ground levels in spite of a lower abundance in pitfall traps. The cumulative species richness for an equal sampling effort was greater in gaps (even in small ones) than in the closed forest. This richness increased with increasing gap area. Some forest species significantly declined in gaps, but none disappeared. Other forest species remained unaffected and several corticolous and arboricolous species were even favoured. Gap area did not significantly affect the forest group. Several open-land species appeared or increased in abundance in gaps. Their colonization was favoured by gap area. The assemblage composition, studied by NMDS and ANOSIM test, clearly differed between gaps (even small) and forest controls. Gaps larger than 0.3 ha were grouped according to the composition and colonization of open-land species. In uncleared gaps, the short-term community dynamics was dominated by colonization rather than local extinction processes.