We document the effect of Mexico City on the epiphytic lichens of Abies religiosa by comparing the communities occurring at Desierto de los Leones, a protected area near to the city, with those at El Chico National Park, a location 100 km upwind (or crosswind) from the city. The first community had 47% fewer species, 62% less lichen cover, and a species abundance pattern that revealed a highly disturbed community. The differences between these communities were greater at the trunk base than at the height of two m, and much stronger when evaluated from a species to species perspective. Among a variety of factors, site air quality may account for many of the observed differences.