As part of Drs. Sally Hacker and Eric Seabloom's labs, Phoebe Zarnetske investigates how invasive beach grasses impact the ecology and geomorphology of Pacific Northwest (PNW) coastal dunes. Over the last century, two non-native beach grasses were introduced to stabilize sand near coastal communities in the PNW (Ammophila arenaria in late 1800's, A. breviligulata in 1935). These introductions led to invasions across the entire dune-back beach system (nearly 50% of the coastline), changing it from a mobile sand environment with patchy native vegetation to large, vegetated and stabilized foredune ridges. Zarnetske's research with Drs. Hacker and Seabloom has shown that removing these invaders to promote the recovery of threatened shorebirds has unintended negative consequences for the native dune plant community. Zarnetske's wind tunnel and species interaction experiments with Drs. Hacker, Seabloom, Ruggiero, and colleagues have shown that each grass differs in its ability to capture sand and build dunes through a feedback between sand supply rates and grass growth habit. These experiments help explain why A. arenaria is associated with taller, steeper dunes, while A. breviligulata is associated with lower, wider dunes. Zarnetske's modeling research has shown that potential further invasions of A. breviligulata are possible, and that while the grasses coexist, A. breviligulata is consistently the dominant species in the system. Combined with field data, this research shows that vegetation plays an important role in shaping coastal dunes through time and space. Further, Zarnetske's research provides valuable insight to help predict changes to dune shape, guide ecosystem restoration efforts, and inform decision-making that balances the need for ecosystem services and ecosystem conservation.
Hacker's lab focuses on coastal community ecology and ecosystem services in systems such as estuaries, salt marshes, coastal dunes, and rocky intertidal.