Does removal of an invasive species restore the disturbance regime and native community on coastal dunes?

Background/Question/Methods

Invasive species can extensively alter disturbance regimes by changing the structure and function of an ecosystem’s biotic and abiotic components.  Introductions and subsequent invasions of European beachgrass (Ammophila arenaria) and American beachgrass (Ammophila breviligulata) to the Pacific Northwest coastal dune ecosystem caused dramatic morphological and ecological changes.  The sand-binding Ammophila species and the dense mats of vegetation they form, changed the natural disturbance regime for native foredune flora and fauna by effectively removing the disturbance of wind-blown sand.  Without the constant sand shifting, late successional species were favored, resulting in an altered community composition, dune morphology, and the loss of native dune flora and fauna.  Currently, habitat restoration efforts for the federally threatened Western snowy plover (Charadrius alexandrinus) repeatedly remove Ammophila species on the foredune, generating flattened areas for nesting.  To investigate whether plover habitat restoration is also restoring the system’s native vegetation community and dune morphology, we completed a series of paired sets of transects inside and outside the plover habitat restoration areas.

Results/Conclusions

When compared with Ammophila dominated areas, we found little evidence for whole-system recovery in the restoration areas.  This suggests that under current restoration efforts, the Western snowy plover cannot act as an umbrella species for the foredune ecosystem.  Rather, a focus on multi-species recovery and restoration of dune geomorphic processes is necessary for whole-system recovery.  Our results have implications for restoration efforts around the world where Ammophila invasions have extensively altered the structure and function of the coastal dune ecosystem.