The effect of coppicing on insect biodiversity. Small-scale mosaics of successional stages drive community turnover

Abstract

Most European temperate woodlands are managed as high forests by clear-cutting or selective cutting. Such forests are shady environments, providing limited opportunities for light-demanding woodland associated organisms. Coppicing has been identified as a suitable tool for biodiversity conservation, because it leads to a spatially and temporally dynamic mosaic of open and closed-canopy successional stages. However, the number of studies on insects is still limited in this respect, and cross-taxon comparisons are needed.We analysed the effect of the successional stage of coppice (time since last felling of coppice layer) on butterflies, moths, and saproxylic beetles, in floodplain coppice-with-standards woods dominated by oak (Quercus robur) and ash (Fraxinus angustifolia) in Lower Austria. We compared species richness, community composition, and life-history traits of the target groups among four stages of coppice: (i) Freshly cut: stands in the first season after felling; (ii) Young coppice: stands 3–7 years after felling; (iii) Mid-aged: advanced stage in 10–15 years after felling with dense undergrowth and high canopy closure; and (iv) Mature: latest stage of coppice, 30–40 years old.We found differences in species richness of butterflies and moths among the stages. Butterfly richness peaked in young coppice and was lowest in dense mid-aged stage. Moth richness was higher in late stages (mid-aged and mature) than in early ones (freshly cut and young). There was no effect on richness of saproxylic beetles. Species compositions of moths and beetles, however, differed among the stages, with the most pronounced difference between early and late stages. The successional stage affected composition of life-history traits of all study groups, showing that the particular stages are exploited by species with different functional/ecological associations to their habitat or by different trophic guilds.The results show that the diversity of all three target groups profited from coppicing. The small-scale mosaic of successional stages created by coppicing supports the existence of diversified communities of insects with both light-demanding and shade-tolerant species. Conservation managers may set variable rotation lengths in order to support threatened species associated with particular stages. In order to further support diversity of saproxylic beetles, conservation management should prioritize maintaining coppice-with-standards woods over simple coppices, some of the standards should be retained to become potential veteran trees in the future, coppice stools should be kept relatively high, and some of the felled trees or larger branches may be left in place on the ground for decay.