Grantee Research Project Results

Increased storm severity and sea-level-rise resulting from climate change have greatly elevated the risk of coastal communities. These risks have been exacerbated by alterations to coastal ecosystems and the introduction of non-native species. In the Pacific Northwest of the United States, coastal dunes protect about one-half of the coastline, and our initial results suggest that increases in wave height and sea level rise could increase the frequency with which waves overtop and erode dunes. Intentional planting of non-native grasses (Ammophila spp.) may have initially increased coastal protection from flooding by building tall foredunes parallel to the shoreline. However, an unintentional second invasion appears to be decreasing foredune height, thereby increasing risk exposure. In addition, many agencies are removing beach grasses to restore habitat for imperiled species. The effects of these conservation actions on flooding risk are unknown. Managers of west coast dune systems are faced with an apparent conundrum. Climate change is increasing the need for the protection services of grass dominated coastal dunes, but conservation mandates the removal of these invasive grasses to favor recovery of threatened and endangered species. Furthermore, the uncontrolled invasion by the second grass, A. breviligulata, is associated with declines in dune height and biodiversity. Despite the conflicting values of coastal protection and conservation, neither invasive species dynamics nor coastal protective values have been quantified under future invasion and climate change scenarios. Here we propose research to address three fundamental objectives: (1) determine the relationship between climate change and beach grass invasion, (2) determine the effects of non-native beach grass invasion on coastal vulnerability, and (3) determine if conservation management alters coastal vulnerability to flooding under a range of climate change, invasion and management scenarios.

We have assembled a large dataset that includes shoreline change, dune geomorphology, and vegetation data necessary to understand the interaction between sand supply, dune grass invader, and the effects on foredune geomorphology (Objective 1). We have collected shoreline change, dune geomorphology, and vegetation data along 77 transects surveyed from Grays Harbor, Washington, to Bandon, Oregon. Analysis shows that dune geomorphology is the result of both sand supply and dune grass species —sites with high sand supply and Ammophila breviligulata as the dominant invader feature shorter and wider dunes compared to sites that have low sand supply and A. arenaria as the dominant invader. We have begun experiments to look at the mechanisms of this interaction. To assess vulnerability to storm waves and sea level we have applied total water level (TWL) models developed by Ruggiero to our dune geomorphology measurements (Objective 2). Our calculations thus far suggest that shorter dunes dominated by A. breviligulata are more vulnerable to overtopping than taller dunes dominated by A. arenaria. We are in the process of resolving the results of different models to understand how foredunes dominated by either species respond to erosion. To assess vulnerability of dunes to various climate change, invasion, and management scenarios, we have developed a number of realistic climate change scenarios relevant to foredune flooding risk (Objective 3). These include sea level rise and increases in wave heights. We have begun to apply these scenarios to current grass invasion dynamics, but in addition, to projected invasion scenarios including the situation in which A. breviligulata dominates along the entire Oregon coast. We have not started the work on applying these models to different management scenarios. Finally, one of us (Hacker) has worked as part of a collaborative group that is considering the functions and services provided by estuarine and coastal ecosystems. The knowledge of dunes gained from this grant has contributed substantially to this broader, international research and we have a number of papers published from this group.

We will continue to collect more data along our transects, maintain our experiments, apply models to our data, write papers, and make presentations at meetings.

Sally Hacker:

http://www.science.oregonstate.edu/~hackers/Site/Homepage.html Exit

Peter Ruggiero:

http://geo.oregonstate.edu/people/faculty/Peter_Ruggiero Exit

Eric Seabloom:

http://www.cbs.umn.edu/eeb/contacts/eric-seabloom Exit