Patterns of arthropod abundance, vegetation, and microclimate at boreal forest edge and interior in two landscapes: Implications for forest birds

The effects of anthropogenic edges on leaf-litter and shrub arthropods were examined in both agriculture and forestry-dominated landscapes in central Saskatchewan, Canada. Microclimate, vegetation, and shrub and leaf-litter arthropods were sampled at south-facing forest edges and interiors of three sites within each landscape. Forest edges in the agricultural landscape were older and had vegetation structures that differed from those in the forestry landscape. This resulted in a sharper contrast in microclimate (temperature and humidity) between edge and interior in forests abutting agriculture than in stands abutting recent clearcuts. Arthropods from the leaf-litter and shrub-layer samples exhibited different responses to edges. In both landscapes, total shrub-arthropod abundance was not significantly affected by edges, while total leaf-litter arthropod abundance was lower at edges than in forest interiors. This reduced abundance of leaf-litter arthropods could negatively affect birds and other insectivorous vertebrates or could have been caused by greater vertebrate predation there. Forest edges in agriculture and forestry landscapes represent relative extremes in edge maturity, demonstrating that age of edges cannot completely mitigate edge effects on microclimate and abundance of arthropods. We discuss the implications of our findings for influences of forest fragmentation and landscape change on forest birds.