Edge responses of epigaeic arthropods to small-scale forest disturbance: Evidence from boreal mixedwood forests adjacent to in situ oil sands development

Oil sands in situ thermal development creates extensive linear and polygonal disturbances that fragment boreal forests and generate complex edge environments. Arthropod assemblages in this context remain poorly understood. This study quantified responses of three epigaeic arthropod taxa to forest edges adjacent to three disturbance types: narrow linear corridors, wide linear corridors, and well pads in fragmented boreal forest. A total of 108,580 individuals representing 309 epigaeic species were collected. Edge effects were taxon-specific and dependent on disturbance geometry. Arthropod abundance exhibited contrasting edge responses with ground beetle and spider catch declining modestly and steeply, respectively, from the edge; whereas rove beetle catch increased from the edge. The spatial extent of edge influence was limited, generally stabilizing within 10 – 35 m of the edge across taxa with no proportional expansion in wider disturbances. Species richness and diversity were comparatively insensitive to disturbance type and distance. Community β-diversity shifted significantly along the edge-interior gradient for all taxa, with greatest dissimilarity within the first 20 m from the edge. Multivariate analysis indicated that environmental gradients, such as soil temperature index, tree basal area, coarse woody material attributes, organic matter thickness, and vegetation structure were highly correlated with arthropod assemblages. These findings demonstrate that edge effects in boreal arthropod communities are spatially constrained, mechanistically correlated with microhabitat conditions, and not predictably scaled by disturbance width or shape. Incorporating fine-scale environmental heterogeneity into reclamation and landscape planning will be critical for mitigating biodiversity impacts in fragmented boreal forest.