The response of corticolous lichens, bryophytes, and vascular plants to anthropogenic edges in northern hardwood forest preserves is compared in east-coast and mid-west (NW Minnesota) sites, using micro-epiphytes on red oak (Quercus rubra) and sugar maple (Acer saccharum). The drastically attenuated lichen flora in the east, apparently due to regional air pollution, restricts the usefulness of these bioindicators, even 120 km from New York City. The forest edge is not necessarily equated with increased light. Established edges may have pronounced shoot growth that shades epiphytes. In the absence of air pollution, lichen and bryophyte species exhibit individual responses to light, humidity, and substrate chemistry. Thus summary variables such as total cover or species richness have limited value as bioindicators of forest integrity.