Anthropogenic influences on epiphytic biodiversity across the Portland urban airshed

Background/Question/Methods

Epiphytic lichens and bryophytes are an important component of Pacific Northwest forest ecosystems, contributing to nutrient cycling, essential forage, and overall biodiversity. The impact of increasing urbanization on forest biodiversity has yet to be fully understood. Urban forests, however, are rapidly emerging as a new model system for examining the potential impacts of global change on forest health. The characterization of epiphytic lichen and bryophyte communities are a well-recognized method for assessing the impacts of air pollution and anthropogenic influence on plant community structure and function. The movement of urban air pollution plumes across rural landscapes suggests that arboreal lichen and bryophyte communities may serve as early indicators of changing air quality and ecosystem function in downwind environments. In this study, I present results of a ground and arboreal epiphytic community analysis that extends along an urban to rural transect from the urban forest of Forest Park, Portland, Oregon to rural Estacada, Oregon. Three research sites with varying distance (0km, 83km, and 117km) from the urban center were sampled and epiphytic community composition was quantified.

Results/Conclusions

As predicted, ground-based surveys showed a shift in epiphytic communities with distance from urban center, consistent with our understanding of airshed dynamics. Epiphytic lichen community composition varied across all sites. Eutrophic lichen species increased with proximity to urban center, while oligotrophic species decreased. The number of cyanolichen species also decreased with proximity to urban center. These preliminary results suggest a regional air quality gradient across these three sites. The results observed here are similar to observations made in other regional bioindication studies, and suggests that an understanding of urban air pollution travel is essential for the preservation of epiphytic community structure and function in rural landscapes. Studies are currently underway to further quantify arboreal bryophyte communities, and to determine the impact altered bryophyte community composition may have on canopy processes. This work further improves our understanding of anthropogenic influence on both ground and arboreal epiphyte communities, and demonstrates the potential influence of urbanization on regional ecosystem services.