RESEARCH:

invasions and ecosystem services

 
 

In the U.S. Pacific Northwest (PNW), the introductions and subsequent invasions of two Ammophila beach grasses caused landscape-scale transformations of coastal dune shape. The grasses created large, continuous, and densely vegetated foredune ridges parallel to the shoreline, replacing the natural sand-shifting and densely vegetated environment. The invasions resulted in threatening the Western snowy plover, and declines in some native plants.


At the same time, the large foredunes created by Ammophila provide an important ecosystem service for humans - coastal protection from overtopping waves. My research investigates both the positive and negative effects of these invasions. I seek to understand the biological and physical mechanisms that influence invasion success, community composition, and dune shape, as well as the implications of removing the invaders. It is especially important to understand these mechanisms and implications in light of documented increases in wave heights, and predictions of sea level rise during climate change.

 

Coastal Dune Research

  1. 1.Beach grass invasions in the U.S. Pacific Northwest

  2. 2.Biophysical feedbacks influence coastal dune shape

  3. 3.Species interactions, environmental gradients, and coexistence

  4. 4.Coastal foredune evolution: evidence for biotic control

  5. 5.Non-target effects of invasive species management

1. Beach grass invasions in the U.S. Pacific Northwest

Along the PNW coast, my colleagues and I documented correlations between coastal foredune shape, dominant beach grass species, and sediment supply rate (Hacker et al. 2011). To uncover the mechanisms behind these patterns, we designed two experiments to characterize the biophysical feedback among beach grass species and sediment supply. The experiments included a large-scale wind tunnel experiment and a mesocosm experiment (Zarnetske 2011, Zarnetske et al. 2012).


We found a species-specific control on foredune shape that is driven by plant morphology and growth responses to sediment supply rate. We determined that the European Ammophila arenaria is the superior dune building species followed by the U.S. East Coast A. breviligulata species, and the native Elymus mollis grass (Zarnetske et al. 2012). This work has led to developing dynamic numerical models that predict species-specific coastal dune shape from community composition.


This research shows strong support for ecological controls on dune geomorphology and coastal protection from waves.

2. Biophysical feedbacks influence dune shape

How do species interactions change along environmental gradients, and in turn, how does this influence invasion potential and species coexistence? To address these questions, I collaborated with ecologists and mathematicians to generate numerical models that examine the influence of beach grass species interactions and sediment supply gradients on PNW beach grass community composition. (Zarnetske 2011).


The models provide key insight about potential future invasion scenarios, including long term community composition and dominant species. When combined with species-specific dune building ability (Zarnetske et al. 2012), this research helps anticipate potential changes in dune geomorphology resulting from changes in community composition, and inform probabilistic models of risk to wave overtopping (Seabloom et al. in press).

3. Species interactions, environmental gradients, and coexistence

O.H. Hinsdale Wave Research Laboratory

Our experimental work shows that biological variables (plant morphology and growth form) as well as physical variables (sediment supply) influence dune shape. How do the relative contributions of biological vs. physical variables change over different time scales? This research focuses on a section of the Pacific Northwest coast, the Columbia River Littoral Cell (CRLC), and combines high resolution data on vegetation community composition, sediment supply rates, and foredune shape along 100 km of coastline, over 21 years (Ruggiero et al. 2011, Zarnetske 2011, Zarnetske et al. in prep).

4. Coastal foredune evolution: evidence for biotic control

Ammophila invasions caused the federal listing of the Western snowy plover (Charadrius alexandrinus nivosus) which prefers bare ground habitat with sparse vegetation. We investigated how nearly 20 years of management targeted at the removal of Ammophila for plover recovery are impacting native plant species and dune morphology along 500 km of coastline in the PNW (Zarnetske et al. 2010).


Despite increased plovers and decreased Ammophila in treated areas, plover habitat restoration also has had the unintentional effect of reducing the richness and abundance of native dune plants. Additionally, frequent Ammophila removal has prevented the re-establishment of the natural disturbance regime and dune function. This research shows that a single-species approach to restoration and management can result in unintended negative effects. We suggest adopting a more synthetic community-wide management approach  (Zarnetske et al. 2010).

5. Non-target effects of invasive species management

Links

relevant papers:

2013, Global Change Biology: Invasive grasses, climate change, and exposure to storm-wave overtopping in coastal dune ecosystems.

2012, Ecology: Biophysical feedback mediates effects of invasive grasses on coastal dune shape.

2012, Oikos: Subtle differences in two non-native congeneric beach grasses significantly affect their colonization, spread, and impact

2011, PhD Dissertation: The influence of biophysical feedbacks and species interactions on grass invasions and coastal dune morphology in the Pacific Northwest, USA.

2010, Ecosphere: Non-target effects of invasive species management: beachgrass, birds, and bulldozers in coastal dunes

main collaborators: Sally Hacker (Oregon State University, OSU), Eric Seabloom (Univ. of Minnesota, UMN), Peter Ruggiero (OSU), Tarik Gouhier (OSU), Vrushali Bokil (OSU), Timothy Maddux (OSU), Jason Killian (OSU), Daniel Cox (OSU), Jeremy Mull (OSU), Aaron David (UMN)

funding: NSF IGERT Ecosystem Informatics, NOAA Seagrant, Hatfield Marine Science Center, O.H. Hinsdale Wave Research Laboratory, OSU Zoology Department, EPA, SERDP.