Isolated trees and forest patches: Patterns in canopy arthropod abundance and diversity in Pinus sylvestris (Scots Pine)

Fragmentation and management of temperate forests has resulted in the creat ion of isolated patches of habitat ranging in size from the single tree to large stands of forest and plantation. Pyrethroid knockdown sampling of can opy arthropods in Pinus sylvestris in a British heathland matrix revealed l arger forest patches (10 ha) supported greater populations of certain arthr opod specialists than small patches (1 ha), and that individual trees suppo rt a qualitatively different fauna with a stronger heathland influence. Fur ther, patch edges differ from patch interiors, particularly with respect to woodland specialist spiders. Feeding guilds differ between edges and inter iors. Scaffold-web building spiders prefer larger patches, whilst aphid spe cies with long rostra capable of penetrating thick exposed cuticle predomin ate on exposed single trees (P = 0.007) and patch edges. Predator densities were lower on single trees (P = 0.024), but there was little evidence of a compensatory increase in density of herbivores. No evidence was found for species-area or density-area effects, suggesting patch heterogeneity with r espect to edge and interior may be relatively important at the scales exami ned. The taxa examined in greatest detail were the Homoptera, Lepidoptera, Symphyta, Coleoptera and Araneae, with the latter group identified to speci es level to examine relationships between feeding guild and patch character . Microclimatic variables related to exposure are proposed to be an importa nt determinant of the patterns observed. (C) 2000 Elsevier Science B.V. All rights reserved.