Urban Forested Parks and Tall Tree Canopies Contribute to Macrolichen Epiphyte Biodiversity in Urban Landscapes

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Urban Forestry & Urban Greening

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Land use changes through urbanization can dramatically impact floral and faunal species-specific survival and alter patterns of regional biodiversity. These changes can lead to complex, ecosystem scale interactions that yield both positive and negative impacts on urban and ex-urban biota. The Pacific Northwest region is one of the most rapidly urbanizing areas of the United States, with the human population estimated to increase more than fifty percent by 2050. Despite rapid population growth in the Pacific Northwest and a forest system known to provide extraordinary ecosystem services, relatively little is known about how human activities affect urban tree biology and the services these trees provide. Specifically, little is known about how urbanization impacts tall tree canopy epiphyte communities, a unique and sensitive component of Pacific Northwest trees which are known to contribute essential ecosystem functions. Here, we revisit a historic study of urban epiphytic lichen communities, initially conducted 18 years ago in Portland, Oregon, USA. Additionally, to compare ground and canopy-based survey methods and to gain a broader understanding of urban epiphytic communities, we comprehensively investigated the biodiversity of stratified urban canopy epiphyte lichen communities, for the first time. Our results show that tall, urban conifer trees and urban parks and forested areas can provide both heterogeneous and stratified habitats for urban-tolerant epiphytic lichens. We found significant and highly eutrophied lichen communities in all epiphytic surveys, suggesting that continued urbanization in the Portland metro region may further impact these communities despite overall gains in regional air quality during the 18 year study period. Our results support the distinct homogenization of urban epiphytic lichen communities, suggesting that it may be necessary to expand beyond measures of biodiversity to consider community composition and functional biodiversity in assessments of the ecology and potential ecosystem services of epiphyte communities within urbanizing landscapes.



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