Across ecosystems, habitat heterogeneity positively influences species diversity. Epiphytes comprise approximately ten percent of the overall vascular flora on earth but, in rainforest canopies, they can contribute substantially to forest diversity. The diversity of epiphytes in tree crowns has been attributed to differences in microclimate, light, and structural characteristics, such as branch size among different areas of the tree crown that create microhabitats to which epiphyte species are specialized. In northern temperate rainforests, non-vascular epiphyte species showed non-random distribution patterns across broad zones within tree crowns but there was little variation in microclimate. Thus, structural characteristics might have a stronger influence on epiphyte distributions than microclimate. To better understand the influence of structural characteristics on non-vascular epiphyte distribution patterns, we surveyed epiphytes on three Acer macrophyllum trees every meter around the trunk from the base to the crown using the point-intercept method. Additionally, one fallen A. macrophyllum tree was surveyed from base to crown. In each tree, three branches were surveyed on all sides. Structural characteristics were noted at each meter to determine the relationship between structural heterogeneity and epiphyte species composition and distributions. Biomass samples from the fallen tree were sorted by species for comparison to percent cover estimates.
Results/Conclusions
We found a significant effect of trunk height on species richness. We also found a significant effect of structure on richness; trunk zones with multiple structural characteristics, such as broken branches and burls, had more species. This relationship was also supported with composition analyses, suggesting that certain species are specialized to different fine-scale substrate and microhabitat types even within a single tree. Branches had significantly different species than trunk zones, aligning with our hypothesis of height and substrate-related preferences. There was a positive significant relationship between epiphyte biomass and percent cover. This relationship was positive for six of seven individual species analyzed. The high structural diversity in northern temperate rainforest trees influenced the fine-scale distribution of non-vascular epiphytes and may explain their coexistence in tree crowns.