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United States Department of Agriculture

Agricultural Research Service


Location: Exotic and Invasive Weeds Research

2012 Annual Report

1a. Objectives (from AD-416):
1) Assess the marsh-wide abundance, distribution and habitat/community characteristics of invasive Lepidium latifolium and endangered Cordylanthus mollis ssp. mollis, before and after implementation of weed management control strategies. 2) Assess weed treatment efficacy, plant community succession, and non-target effects across environmental gradients within the marsh. 3) In pilot scale experiments, test alternative approaches for weed control in sensitive areas where invasive weeds directly interact with vulnerable endangered plants. 4) Conduct demographic-based research to evaluate weed response to management actions, and to diagnose causes of poor population performance of native plants, and provide biologically based data for integrated weed management strategies and endangered plant recovery.

1b. Approach (from AD-416):
GPS technology will be used to record geospatial data on population size, distribution, and habitat conditions of target weeds and endangered plants at Southampton Bay Natural Preserve, Benicia, California. Random control and treatment plots will be stratified by discrete within-marsh hydrogeomorphic settings that correlate with observed phenological differences in Lepidium latifolium growth. Baseline evaluation will include evaluation of L. latifolium stem density, biomass and plant community associates, and sediment physico-chemical characteristics. Post-treatment evaluations will track changes in weed density, biomass and community succession to evaluate efficacy of management actions, and the need for adaptive change in approach. A life table response experiment (LTRE) will be conducted to evaluate weed demography and the direct response of soft bird’s-beak to Lepidium alternative weed control approaches. C. mollis ssp. mollis individuals in 0.25m-2 plots within Lepidium invaded subpopulations (treatment plots) will be tagged, and survivorship and life stage transitions will be recorded. At the end of the annual life cycle, fecundity of C. mollis will be quantified. Management option impacts on C. mollis population growth rates and survivorship will be compared. Results will be directly applicable to weed control strategies, conservation management, ecological restoration and endangered plant recovery efforts.

3. Progress Report:
The agreement was established in support of Objective 1 of the in-house project, the goal being to develop effective weed control efforts that facilitate the recovery of soft bird’s-beak (C. mollis), a federally listed endangered tidal marsh plant that is directly impacted by perennial pepperweed (L. latifolium). In FY12, ARS scientists from Davis, California, tracked the phenological development of pepperweed to determine optimal time for herbicide applications. They assessed the distribution, abundance and habitat characteristics of pepperweed and soft bird’s-beak before and after annual weed management. In FY12, they tagged 144 rare plants in treatments with and without pepperweed or management, and with herbicide treatments to evaluate demographic responses and parameterize a model for management of endangered plant recovery. In experimental plots, they collected live biomass and density data to evaluate efficacy of alternative management methods (hand spraying/wicking). Before treatment, 57% of the occupied area had ~100% cover of pepperweed. Following three years of treatment, occupied area has been significantly reduced and 71% of the originally invaded area has been reduced to stands with low density and cover. In FY12, ARS scientists quantified a 163% increase in the population size of the endangered plant since the baseline year. These results demonstrate weed management actions can be modified and successfully implemented in sensitive tidal wetlands without disturbance to endangered plant populations. FWS is using the project as a model for an expansion of weed management efforts in endangered species habitat throughout the San Francisco Estuary.

4. Accomplishments

Last Modified: 07/26/2017
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