DISSERTATION RESEARCH: Assessing urbanization impacts on canopy epiphyte biodiversity and function in Pacific Northwest forests.

Portland State University, Portland OR

Investigators

Abstract

--------------------------------------------------------- DISSERTATION RESEARCH: Canopies in the urban cloud: assessing urbanization impacts on canopy epiphyte biodiversity and function in Pacific Northwest forests While relatively small in size, the lichens and mosses growing in forest canopies in the Pacific Northwest have a big impact on how the forest works. One role they perform is the cycling of nutrients in these forested ecosystems. Although important, lichens and mosses are especially sensitive to the fallout from urban pollution. Preliminary studies indicate that exposure to urban pollutants may lead to dramatic shifts in the moss and lichen communities in forest canopies of the Pacific Northwest, including the total loss of very sensitive, yet ecologically important, lichens that can capture nitrogen from the air. Although the extreme sensitivity of these lichens makes them particularly vulnerable to atmospheric pollution, to date there has been no study to assess the impacts of the spread of urban environments on these forest canopy lichen communities or how nutrients are used in the canopy. This is particularly important as transportation and transportation-sourced pollutants increase throughout the Pacific Northwest. This research will create important new understanding of the impacts of growing urban environments on nearby tree canopies and forested ecosystems of the Pacific Northwest. The results obtained here will be useful to estimate how much nitrogen forests receive through pollution. Collectively, these efforts will aid researchers and government agencies in identifying canopy areas at risk of being damaged around the rapidly increasing urban centers in the Pacific Northwest. Biodiversity loss associated with human alteration of ecosystems is a major planetary concern, and rapid expansion of global urban areas contributes to this loss. Urbanization can replace endemic species with widespread generalist species, creating a homogenized ecosystem with resulting impacts on ecosystem function. While many studies have identified land-use change as the main driver of terrestrial biodiversity loss, relatively few studies, to date, have explored how the transport and exposure of urban air plumes to downwind ecosystems may also be driving modern biodiversity loss. The Pacific Northwest is known for its many pristine, and iconic, coniferous forests that harbor an immense biomass and biodiversity of canopy epiphytes (lichens and mosses). Recently, the Pacific Northwest has experienced rapid population growth and many endemic tree canopy epiphytic species are extremely sensitive to the increasing effects of urbanization (increasing reactive nitrogen and heavy metal deposition). This research aims to assess how urban-induced shifts in epiphyte community structure influence Pacific Northwest forest ecosystem process by examining how community shifts in canopy epiphytes affect canopy nitrogen cycles. This study will address how rates of canopy cyanolichen nitrogen fixation vary across an established regional urbanization gradient and address the overall contribution of moss-associated nitrogen fixation potential in Pseudotsuga menziesii tree canopies, a previously unidentified source of canopy nitrogen fixation in Pacific Northwest forests.