Structural indicators of spider communities across the forest plantation cycle

Abstract

Given the expansion of plantation forests in Ireland over recent years, there is a need to assess their impact on biodiversity and to identify how sustainable forest management strategies can incorporate biodiversity. We aimed to assess the impact of plantation forests on spider communities and identify structural indicators of their diversity. Pitfall traps were used to sample spiders in Sitka spruce (Picea sitchensis) and ash (Fraxinus excelsior) plantations at different stages of the forest cycle and cover of vegetation, dead wood and soil organic content were measured within each site. Ordinations revealed that spider assemblages were separated by both forest development and canopy species across the forest cycle. The pre-thicket ash and spruce assemblages were similar, whereas canopy species had a greater effect in the more structurally developed stands. The mature ash plots formed a distinct group from the other stands. Overall species richness was highest in the spruce and ash pre-thicket stands, and in the mature spruce stands with a more open canopy.Mature ash stands had the lowest species richness. Lower field layer vegetation was positively correlated with total spider species richness and open habitat specialist species richness whereas canopy closure had a negative effect on these species variables. Forest spider species were positively correlated with litter cover, depth and twig cover. To enhance the diversity of open and forest spider species within a stand, the growth of lower field layer vegetation should be encouraged at all stages of the forest cycle, whilst retaining features typical of a mature forest. Within a plantation, a mosaic of different aged stands will sustain both open and forest specialists to enhance diversity. The distinct assemblages found in the mature plantations indicate that on a landscape scale, the establishment of both ash and spruce plantations will enhance overall diversity.

Identifying practical indicators of biodiversity for stand-level management of plantation forests

“…Birds range over wider areas than members of any of the other taxa, and are therefore affected by environmental variation at the plantation and landscape scales (Pithon et al 2005). Species assemblages present in the sites surveyed are analysed in more detail in related work (French et al in press;Oxbrough et al 2005;Smith et al 2005;Wilson et al 2006). …”

“…For further details on survey methodology, see French et al (in press) for vegetation, Oxbrough et al (2005) for spiders, Wilson et al (2006) for birds and Smith et al (2005) for all taxonomic groups, environmental and management data and overall study design. Nomenclature follows for mosses, Stace (1997) for vascular plants and Beaman (1994) for birds.…”

“…(Day et al 1993;Fahy and Gormally 1998;Humphrey et al 1999;Oxbrough et al 2005) and birds (Currie and Balmford 1982;Bibby et al 1989;Duffy et al 1997;O’Halloran et al 1999). …”

“…Dispersal is an important mechanism in the succession of forest vascular plants, as demonstrated by the relationship with proximity to old woodland. For spiders, whose young can disperse long distances by ballooning, a more important factor may be the development of suitable habitat in the form of high cover of conifer litter or bryophytes (Table 9; Oxbrough et al 2005). For birds, dispersal is likely to be much less important than the development of suitable or unsuitable forest structures with age.…”

Communities of ground-living spiders in deciduous forests: Does tree species diversity matter?

“…In addition to these biotic interactions, spider communities are influenced to a large degree by abiotic environmental factors comprising structural and microclimatic features of the habitat (Hatley and MacMahon 1980;Uetz 1990;Niemelä et al 1996;Gurdebeke et al 2003;Oxbrough et al 2005), which in turn might be affected by forest stand diversity (e.g. via litter diversity and differing decomposition dynamics).…”