Spartina Eradication Plan
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H. T. HARVEY & ASSOCIATES ECOLOGICAL CONSULTANTS Humboldt Bay Regional Spartina Eradication Plan Final Report Project # 3192-01 Prepared for: Joel Gerwein, Project Manager California State Coastal Conservancy 1330 Broadway, 13th Floor Oakland, CA 94612-2530 Prepared by: H. T. Harvey & Associates 5 April 2013 1125 16th Street, Suite 209 Arcata, CA 95521 Ph: 707.822.4141 F: 707.822.4848 Executive Summary This Draft Humboldt Bay Regional Spartina Eradication Plan (Regional Plan) describes an approach for eradicating invasive cordgrass (genus Spartina) at a regional scale. In their non-native ranges, invasive Spartina species displace native plant species, reduce biodiversity, disrupt natural ecological function, and alter habitats for fish and wildlife species. Spartina eradication in the Humboldt Bay region is needed to restore sensitive coastal wetland habitats and to eliminate the threat of spread that untreated Spartina poses to other estuaries on the West Coast. This Regional Plan presents a toolbox of control methods to address infested wetlands at different stages of treatment with varying site characteristics. The control methods presented are based on demonstrated effectiveness and ongoing research. We embrace an adaptive management approach, which will allow us to make plan changes in response to new information, treatment successes and failures, funding opportunities, logistical constraints, and other unforeseeable factors. The region covered in this plan is called the Management Area, and includes Humboldt Bay and the Eel and Mad River Estuaries, on the northern California coast. Regional Spartina eradication is part of a larger West Coast collaborative eradication extending from British Columbia, Canada to California. In 2010, the coast- wide Spartina Action Coordination Team (ACT) identified Spartina eradication in the Management Area as a high priority task, noting that increased focus is needed in this region to achieve eradication success. The importance of coordination, political will, and adequate funding has been demonstrated at several other sites of Spartina invasion (such as Willapa Bay, Washington and the San Francisco Estuary, California) where coordinated programs have resulted in nearly complete Spartina eradication (Boe et al. 2010). This Regional Plan is consistent with critical elements that ACT identified as needed for all regions, including eradication of existing Spartina infestations, habitat restoration, prevention, early detection, rapid response to new invasions, and communication and outreach. Additionally, this Regional Plan addresses factors unique to the Management Area that affect how Spartina can be eradicated, as compared to other eradication methods and efforts on the West Coast. Factors unique to the Management Area include: • The Management Area currently contains just one species (S. densiflora) of the 4 non-native Spartina species that have invaded other areas of the West Coast. • S. densiflora has infested 1672 acres since its inadvertent introduction to Humboldt Bay in the 1870s, representing the oldest and most extensive occurrence of this species on the West Coast. • Approximately 90% of tidal marsh habitat in the Management Area has been invaded by S. densiflora to some extent, with evidence that the invasion is still progressing. • Continuing encroachment by S. densiflora threatens high elevation salt marsh, a diverse plant community that provides habitat for rare plant species, and that is already scarce in the Management Area. • Encroachment into mudflat habitats is becoming evident in some locations within the Management Area. S. densiflora does not extend as low in the intertidal zone as the invasive S. alterniflora, which Final Humboldt Bay Regional H. T. Harvey & Associates i Spartina Eradication Plan 5 April 2013 rapidly converted over 9,000 acres of mudflat habitat into dense cordgrass meadows in Willapa Bay before eradication by coordinated regional efforts there. • No native Spartina species occur in the Management Area. The only Spartina species that naturally occurs on the West Coast is S. foliosa, and its range extends only as far north as Bodega Bay, California. In the San Francisco Estuary, hybrid crosses between S. foliosa and invasive Spartina species (especially S. alterniflora, but also S. densiflora) pose a major management challenge. • S. densiflora is less responsive to herbicide treatments then other invasive Spartina species, leading ACT to prioritize the development of improved treatment methods for this species (Boe et al. 2010). • Mechanical treatment methods that effectively kill established stands of S. densiflora in 2 years have recently been developed and continue to be refined; substantial recovery by native plant communities following treatment has been documented. • Various combinations of chemical and mechanical methods are currently under investigation in the Management Area, having been used effectively to treat S. densiflora elsewhere. • Approximately 20% of lands infested by S. densiflora in the Management Area have received some level of treatment to date. This Regional Plan is intended to expedite current eradication efforts and provide regional coordination. This Regional Plan calls for an agency or other entity to be designated to perform regional coordination, appropriately referred to as the Regional Coordinator. The Regional Coordinator will be responsible for coordinated implementation of the Regional Plan, and will provide the long-term presence and commitment needed to eradicate Spartina. The Regional Coordinator will coordinate and lead acquisition and administration of funding, permitting, planning, implementation, monitoring, communication, and outreach. Public agencies will support the Regional Coordinator’s efforts; private landowners are not expected to fulfill these responsibilities, although willing landowners will be encouraged to participate. The Regional Coordinator will be the main communication conduit and hub among all Management Area parties involved. The Regional Coordinator will share information on work accomplished at the regional level and will collaborate with other West Coast managers who are eradicating invasive Spartina. The Humboldt Bay Harbor, Recreation and Conservation District has been identified as a possible agency to serve as the Regional Coordinator, with support from several additional agencies and non-governmental organizations. The California State Coastal Conservancy (Conservancy) will provide scientific and permitting support and may fund some of the eradication measures and/or help the Regional Coordinator acquire funding for implementation. The Humboldt Bay National Wildlife Refuge will provide scientific and logistical support, and a regional Spartina advisory committee may be formed to foster interagency and community communication and participation. The intended readers and audience for this Draft Regional Plan are resource managers, resource agency staff, landowners, and the local community and public. Sections 1 to 3 provide background information, including an overview and Regional Plan’s policy context; a description of the general physical geography of the Final Humboldt Bay Regional H. T. Harvey & Associates ii Spartina Eradication Plan 5 April 2013 Management Area; and information on Spartina ecology and the ecological impacts of Spartina invasion, with a focus on S. densiflora. Sections 4 to 6 present details on how regional Spartina eradication can be achieved; readers who are primarily interested in potential Spartina control actions in the Management Area should focus on these sections. The eradication strategy includes a discussion of the steps needed to eradicate existing invasive Spartina and enhance native plant communities; procedures for minimizing reinvasion; guidelines for monitoring; and means of communication and outreach. An overview of permits that will likely be required to perform eradication work is presented, with discussion of how permitting can be facilitated through coordination at a regional level. Lastly, a characterization of costs associated with plan implementation is provided. Extensive background information was gathered in the process of preparing this Regional Plan, and much of it is included in appendices (Appendices A to C). The Conservancy is the lead agency responsible for complying with the California Environmental Quality Act for regional Spartina eradication. A Programmatic Environmental Impact Report (PEIR) (CSCC 2012) is being prepared concurrently with development of this Regional Plan to assess potential environmental impacts and recommend mitigation measures to avoid, minimize, or mitigate impacts. Both the Draft Regional Plan and the PEIR will be available for public review and comment. Final Humboldt Bay Regional H. T. Harvey & Associates iii Spartina Eradication Plan 5 April 2013 Table of Contents Executive Summary ............................................................................................................................................................. i Table of Contents .............................................................................................................................................................. iv List of Contributors .......................................................................................................................................................... vii Acknowledgements .........................................................................................................................................................