Most lichen produce secondary compounds that have a variety of functions, including pathogen resistance, deterrence of herbivory, and protection from irradiance. In lichen, production of a given secondary compound is a taxonomically significant trait. Thus, community composition may be strongly affected by ultraviolet light exposure, since certain species are able to produce UV-screening compounds while others cannot. To determine the effect of UV exposure on lichen communities, lichen morphospecies were sampled in pasture, forest edge, and forest interior environments and assayed for the presence of UV-absorbing secondary compounds. The Shannon-Weiner diversity index of UV-screening compounds was significantly higher in the pasture than in the forest edge and than in the forest interior. However, the forest edge and interior communities did not differ significantly from one another with respect to diversity of UV-protective compounds. This is persuasive evidence that a sufficient intensity of UV exposure is a significant factor in determining the species composition of lichen communities. Therefore, altering light intensities within a forest (e.g. through fragmentation or selective deforestation) may alter lichen community composition if the change in the light regime is sufficiently dramatic.