The influence of forest landscape composition and structure on spider communities in Mafra (Portugal) and Hamsterley forest (England, United Kingdom)

Abstract

The present work proposed to evaluate the effects of land use and fragmentation on spider diversity and community structure. In Portugal, Oak, Pine, Eucalyptus and Shrubland were sampled to study the effects of habitat complexity on diversity, while abundance and richness were analyzed across a Eucalyptus-Grassland ecotone. In England, assemblage structure and diversity were assessed in different aged blocks of Sitka spruce and Oak woodland. Multivariate analyses were used to classify and ordinate data to assess the influence of measured environmental variables on spider distribution. Estimated values of richness calculated using non-parametric estimators confirmed that richness increased in areas with decreasing levels of disturbance. Using CCA, both crown cover and soil pH significantly influenced spider distribution in the forest areas. Across a Eucalyptus-Grassland ecotone, both abundance and richness were highest in Grassland, with spider abundance greatest 10m away from the boundary, and estimated richness highest at the Grassland-edge. A high degree of mixing was observed between the two habitats, with no apparent edge-associated species. Along a successional gradient in Sitka spruce, the number of species decreased with increasing plantation age, and was linked to the concomitant loss of vegetation complexity with increased canopy closure. Finally, 23 additions to the Portuguese checklist are provided.