Oregon’s coastal foredunes were first altered in the early 1900s by the introduction of two non-native grass species (Ammophila arenaria and Ammophila breviligulata), which significantly changed the landscape and shaped the dunes into what we see today. There are six coastal communities in Oregon with official dune management plans that allow for dune grading (i.e., flattening) and other types of dune management/maintenance to preserve viewsheds and reduce sand inundation. These management practices and the use of the non-native grasses to stabilize the sand affect both the dune ecosystem and physical morphology, and there is a growing need to quantify and understand the effects of the management techniques and how much sand the different types of dune grasses trap.

We are working to (1) determine when coastal foredunes have been graded and replanted in the last two decades by detecting vegetation cover change on aerial imagery, and (2) collect and analyze topographic data to explore the differences in managed and unmanaged dune morphology. The results will be included in a new Oregon Coastal Dunes Management Guidebook, along with a synthesis of the best-available science to guide future foredune management practices.

Part of a system in Nehalem dune system in Oregon, USA was graded in February 2021 to promote nesting spaces for native shore birds. We took advantage of this opportunity to set up a common garden experiment involving native and non-native species. Nine 20x10m plots were set up, with 4 mono species plots, 2 poly species plots and 2 control plots with no vegetation. The morphology of the area is monitored bimonthly and vegetation characteristics are monitored seasonally in order to understand the capacity of species to trap sand and build dunes. All these data feed into the sand transport model, AeoLiS, which we are working to develop and make changes to to implement species-specifics characteristics on sand trapping and better understand the evolution of coastal dunes in the longer term.

Related Pubs:
Dickey, J., Wengrove, M., Cohn, N., Ruggiero, P. and Hacker, S.D., 2023. Observations and modeling of shear stress reduction and sediment flux within sparse dune grass canopies on managed coastal dunes. Earth Surface Processes and Landforms.

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