The initial effects of afforestation on the ground-dwelling spider fauna of Irish peatlands and grasslands

Across Europe, the majority of afforestation is carried out on former agricultural land. Given this current planting trend it is important to assess the impact that afforestation will have on the flora and fauna of habitats typically used for afforestation. The study aim was to investigate the initial effects of afforestation (5 years after planting) on the ground-dwelling spider fauna within three habitats (peatlands, improved grasslands and wet grasslands) in Ireland. A paired sampling approach was used where 24 pairs of unplanted and planted sites (eight within each habitat type) were matched for habitat, vegetation type, soil properties, and geographical location. The planted sites were comprised of 5-year-old stands of Sitka spruce (Picea sitchensis). Within each habitat pitfall traps were established in areas of vegetation cover representative of the site as a whole, as well as in supplementary features which may also contribute to the biodiversity of a site, for instance in hedgerows, wet flushes, and the edges of ditches or streams.During the study 33,157 spiders were collected in 189 species and 18 families. Forty species sampled were associated with open habitats whereas 15 species were associated with forested habitats, 54 species were associated with wet habitats whereas two species were associated with dry habitats. Across the habitats fewer wet-associated species and fewer rare species were supported after afforestation. In particular areas of wet flush in the peatlands supported a unique and diverse spider fauna which was lost after afforestation. In contrast, the planted improved grasslands were more species rich, and supported a greater number of spider species associated with low vegetation than comparable unplanted sites. The hedgerow spider fauna did not differ notably in assemblage composition between the unplanted and planted sites. This study suggests that even in the early stages of the forest cycle (first 5 years) there is a change in the spider fauna, with the rare or specialist species being replaced by habitat generalists or species associated with forested habitats. It is also suggested that peatlands are particularly sensitive to afforestation, indicating that in terms of biodiversity loss, this habitat is the least suitable for afforestation.