Aspect and vertical distribution of lichen species on Populus grandidentata.

Abstract

In summary, all species differ in their requirements of the particular balance of light and moisture, their ability to effect anchorage, and perhaps their ability to compete with other species. The more ubiquitous species are those with the broadest tolerances, while the more restricted species, whether in vertical distribution or in aspect, are presumably those with the most rigid requirements. It is this spectrum of varying tolerances, preferences, and requirements, which determines the distributional patterns of corticolous lichens.