Short-term effect of windstorm disturbance on saproxylic beetles in broadleaved temperate forests - Part I: Do environmental changes induce a gap effect?

Windstorm created small gaps with large amounts of sun-exposed dead wood in managed oak-hornbeam forest in France in 1999. The short-term effect of these gaps for saproxylic beetle abundance, species richness and assemblage composition were compared with closed-forest stands and seedling-sapling stands. We observed a strong differentiation of saproxylic assemblage in gaps compared with undisturbed stands but richness was only slightly higher in gaps. Contrary to expectations, the abundance of primary wood consumers on the whole, highly dominated by bark beetles, was as high in undisturbed plots as in gaps. However, longhorn and buprestid beetles responded positively in gaps. The later-successional xylophagous beetles on the whole were not significantly less abundant in gaps, in spite of the lower abundance of some shade-preferring species (Anobiidae, Eucnernidae, Melandryidae). Gap changes had a positive impact on the floricolous and xylomycetophagous insects, even if the species response was contrasted. Saproxylic communities were also distinct in gaps and in seedling-sapling stands. Both species richness and number of characteristic species were higher in gaps than in seedling-sapling stands. The abundance of later-successional xylophagous and xylomycetophagous insects was equal in gaps and in seedling-sapling stands. The abundance of saproxylic predators seemed to follow the population levels of all xylophagous insects. Because of their richness and faunistic dissimilarity with other open stands and closed-canopy controls, uncleared gaps may enhance the gamma diversity at the forest scale. In response to management issues underlying this research project, saproxylic diversity would benefit from the maintenance of some uncleared gaps. Moreover, in managed temperate, deciduous forests, my results suggest to retain more sun-exposed harvesting residue in fellings in order to enhance biodiversity. (c) 2005 Elsevier B.V. All rights reserved.