Can spruce plantations support a diverse, forest-associated arthropod fauna?

Plantation forests constitute a large proportion of the forest estate in many countries, particularly in the temperate regions of Europe. In countries like Britain and Ireland, a large proportion of these plantations are comprised of non-native conifers, particularly Picea sitchensis and Picea abies. Furthermore, cover of natural woodlands is declining and they are becoming increasingly fragmented within intensively managed agricultural landscapes. In light of this, it is important that the potential of these plantations to support a diverse flora and fauna, particularly of forest-associated species, is assessed. We compared arthropod diversity in pure stands of P. sitchensis and P. abies, and also in P. abies mixed stands with native species to that in native woodlands in forty five sites across Ireland. Spiders and Carabid beetles were sampled with pitfall traps and moths were sampled using light traps. A range of environmental parameters were measured including vegetation cover, stand structure, soil attributes, and landscape variables such as forest cover. Invertebrate species composition and richness differed between plantations and native woodlands, particularly for key forest-associated species. However, conifer dominated stands mixed with native species did not support fauna associated with semi-natural woodlands. Responses also differed by taxonomic group. At the stand scale arthropods were related to litter and vegetation cover, whereas amount of forest cover within 1km was important for moths. These findings suggest that forest policy aimed at promotion of biodiversity in plantations should support greater diversity of stand structure and tree species composition. Although planting of species of native provenance has increased in recent years, particularly in mixed stands, this trend should be encouraged further, by increasing the proportion of these species in a mix.