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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, 2024

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. 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. Two case studies will be performed. The first supports restoration of wetland vegetation in the San Francisco Bay-Delta Estuary. Four yellow flag iris invasion sites along an estuarine salinity gradient will be identified to assess occurrence and abundance of plant species and functional groups relative to environmental variation and level of invasion. Persistent native plant associates within invaded plots suggesting some degree of resistance to invasion will be identified. Experiments will follow to assess competitive outcomes and strength of interactions between native species, plant functional groups, and the iris relative to environmental conditions, and the capacity of native species to provide invasion resistance in a restoration context. Iris will be introduced into plant species pools to evaluate invasion resistance. The Cooperator will assess traits and ecological roles of yellow flag iris at four populations in its native range, along an estuarine gradient in the Guadalquivir Estuary. The Cooperator will also conduct 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. . 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 range through comparative analyses. In a second study, a planned tidal wetland restoration project in the Eel River Estuary, northwestern California coast, provides a model study system for evaluation of plant community restoration methods to support enhanced ecosystem services through rapid carbon (C) sequestration during colonization by wetland vegetation. Restored tidal wetlands potentially accrete at high rates and sequester more C than natural wetlands in equilibrium with sea level rise, but C sequestration is influenced by the productivity and C content of colonizing vegetation. New tidal wetland restoration sites are often rapidly invaded by alien plant species that are often the earliest colonizers of newly disturbed sites. Dense-flowered cordgrass is a problematic weed along shores of Eel River Estuary tidal sloughs, pointing to the need to study the impacts of invasive cordgrass and alternative native vegetation on C sequestration to support the restoration goals to enhance ecosystem services. The Cooperator and ARS will conduct pre-restoration baseline studies to quantify baseline C pools and sequestration rates in marsh sediments using Verified Carbon Standard methodologies for tidal wetlands, and in standing plant biomass.