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ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Invasive Species and Pollinator Health » Research » Research Project #438655

Research Project: Reducing the Impact of Invasive Weeds in Pacific West Estuaries through Plant Community Restoration

Location: Invasive Species and Pollinator Health

Project Number: 2030-22300-032-019-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Sep 15, 2020
End Date: Sep 14, 2025

Our goal is to assess and develop plant community restoration approaches to resist weed invasions, enhance ecosystem services, and improve integrated weed management (IWM) and restoration outcomes with primary focus on European yellow flag iris (Iris pseudacorus) in tidal wetland ecosystems. Focal weeds include alien yellow flag iris (European Iris pseudacorus) and dense-flowered cordgrass (South American Spartina densiflora) in tidal wetland ecosystems. The ultimate goal of IWM in natural areas is to restore and conserve native plant communities that contribute to invasion resistance, yet plant community restoration efforts typically do not include invasion prevention measures. Under climate change, survival of plant species and assembly of plant communities in a restoration context will depend on novel community interactions and environmental processes. Environmental variability coupled with biotic interactions such as interspecific competition can influence the invasibility of restoration sites and their resilience to recover once invasive species have been removed. Establishment and persistence of desirable vegetation following weed removal requires knowledge of the distribution of plant species relative to variation in environmental conditions. Knowledge of plant species that have traits that confer an advantage that have allowed them to persist with invasive weeds with ongoing selection within resident populations can provide an evolutionary advantage in a restoration context. Identification of adapted native species and their plant traits, and improved understanding of environmental interactions that promote their persistence within invaded communities is an important first step towards understanding how to assemble invasion-resistant plantings to increase restoration success. Understanding the relationships between spatial environmental variability, plant species occurrence, the functional roles that both alien and native species play within the plant community, and the outcome of their interactions is needed for restoration strategies to prevent new infestations following management to remove weeds. In addition, increasing our knowledge on key plant traits of native and invasive species will provide critical knowledge for optimal design of restoration efforts to maximize ecosystem services such as biodiversity, water purification and atmospheric carbon sequestration.

The Cooperator and ARS will evaluate restoration approaches that confer resistance to weed invasion, improve the outcome of integrated weed management (IWM), and restore ecosystem services in invaded estuaries of the Pacific West region. This effort complements new ARS research to assess IWM alternatives for restoration managers. A multi-faceted case study will be implemented to improve understanding of the invasiveness and impacts of invasive yellow flag iris (European Iris pseudacorus) to support restoration of vegetation in the San Francisco Bay-Delta Estuary. Dr. Castillo will assess traits and ecological roles of yellow flag iris at five populations in its native range, along an estuarine gradient in the Guadalquivir Estuary. In California the team will collaborate on a parallel assessment in the invaded range. The team will collect data on I. pseudacorus abundance and the community composition of vegetation and will evaluate and compare the impact of the focal species on plant community diversity at study sites in both occupied ranges. Persistent native plant associates co-occurring with iris, suggesting some degree of resistance to invasion, will be identified and key functional traits and functional groups of these species will be evaluated. Insight into the role of pre-adaption for invasion will be gained by comparing the functional composition of species pools across environmental gradients in the native range to those in the invaded San Francisco Bay-Delta Estuary through comparative analyses. The Cooperator will participate in evaluation of germination requirements of the iris in the invaded range, and pollination ecology in both ranges. The Cooperator will also analyze the data obtained in a common garden experiment in Spain, including plants from native and invaded range study sites, to investigate traits and differences in growth form among populations that influence plant community composition and diversity. The Cooperator will also collaborate on evaluation of a 2-year common garden experiment conducted in California using invasive alien iris populations to better understand biomass allocation, survival and traits at juvenile, pre-reproductive, and reproductive life stages of the plants. Dr. Castillo will also collaborate on assessment of wetland plant communities impacted by invasive Ludwigia hexapetala in freshwater wetlands at California’s Laguna de Santa Rosa watershed. Results from studies of invasive Iris and Ludwigia spp. will be used to design future experiments to assess competitive outcomes and strength of interactions between the invasive and native species, plant functional groups relative to environmental variables environmental variable. Collectively these results will provide knowledge of the capacity of native species to provide biotic resistance to invasion in an IWM-restoration context. The Cooperator will contribute data analyses and collaborate on manuscripts reporting results for publication in scientific journals, and presentations at scientific conferences.