Non-vascular epiphytes have been determined to grow in a non-random distribution in the canopies of Acer macrophyllum in the Hoh Rainforest, Washington. Nitrogen (N) source has been suggested as a potention driver of the distribution, and stable isotopic analyses were used to consider the influence of this factor. Three epiphyte species, the lycophyte Selaginella oregana, and bryophytes Rhytidiadelphus loreus, and Neckera douglasii, and four trunk dwelling species, Selaginella oregana, and the bryophytes Hypnum subimponens, Leucolepis acanthoneuron, and Metaneckera menziesii, were selected for analyses on the basis of their distribution on five host trees. Samples of plant tissues, as well as canopy and trunk soil were analyzed using isotope ratio mass spectrometry to identify the N source of each species. N source varied significantly by species and growing location. δ15N values of all bryophyte species confirmed an atmospheric N source. Results for the lycophyte S. oregana varied significantly in response to its relationship with R. loreus, which grows above it in mats in the inner canopy. Selaginella oregana appears to use canopy soil N in the presence of R. loreus, and atmospheric N in its absence on the trunk. These findings suggest the role of niche partitioning in the coexistence of S. oregana and R. loreus within the canopy, and illustrate the likely ability of S. oregana to vary its N source based on competition for the resource. No study of this kind has been conducted in the Hoh Rainforest to date, and this work highlights the intersection of abiotic and biotic factors in determining epiphyte species distributional patterns in the temperate forest ecosystem.