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United States Department of Agriculture

Agricultural Research Service


Location: Exotic and Invasive Weeds Research

2009 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, CA. Random control and treatment plots will be stratified within 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. Documents Reimbursable with DOi- Fish & Wildlife. Log 39319.

3. Progress Report
The Sacramento-San Joaquin Delta is the largest source of California’s water for agricultural, urban and industrial use. Irrigation and other Delta water diversions depend on sustainable management and recovery of the San Francisco Estuary that has been impacted by aquatic weeds. Let unchecked, propagules of aquatic invasive weeds in natural systems are hydrologically dispersed and can colonize agricultural and natural ecosystems throughout the watershed. The first record of exotic Lepidium latifolium (perennial pepperweed) in California is from Yolo County, from which it spread to the Delta and San Francisco Estuary, and to western crop and rangelands. While extensive research has focused on perennial pepperweed control in rangelands, little attention has been devoted to its control in aquatic systems. A 3-year research project entitled “Lepidium latifolium management for endangered species and tidal marsh recovery” was initiated in summer 2009, to provide science support for effective weed control efforts that facilitate the recovery of a federally listed endangered tidal marsh plant directly impacted by perennial pepperweed, and the impacted native plant community. This partnership with US-FWS and California Dept Parks & Recreation (DPR) provides ARS research support to evaluate efficacy of management actions for control of invasive pepperweed and their influence on the occurrence, demographic performance and recovery of endemic plant species to North Bay - San Francisco Estuary marshes within the federal Solano Water Project service area. To date, we have collected baseline data prior to DPR’s initiation of weed control actions in spring 2010. Using GPS technology, we mapped the 2009 pre-control distribution of L. latifolium within the preserve, and recorded weed abundance classes and microhabitat types for each patch. We also mapped the baseline distribution and abundance of endangered soft bird’s-beak (Cordylanthus mollis), and collected data on it abundance, habitat position, and plant community associates. Using these data, we established rare plant protection zones per FWS criteria for DPR herbicide application actions in 2010, and to plan life table response experiments to be initiated in 2010. We initiated baseline demographic monitoring of the rare plants with and without pepperweed, tagging 200 individuals within a total of 5 sub-areas, and 40 randomly chosen subplots stratified by marsh inundation zones, and we are tracking their growth and survivorship through the season (through mid-November). We stratified the preserve by pepperweed occupied microhabitat type (upland-wetland ecotone; channel edge), and also by tidal inundation gradient (bay shore, mid-marsh, upper marsh). We randomly selected four 10m X 4m plots within each of 2 microhabitats and 3 marsh zones for a total of 24 efficacy evaluation plots. Within these plots, we measured pepperweed stem density and biomass, plant community composition, and collected sediment cores for physico-chemical evaluation. Seasonal demographic monitoring and sample analysis are still in progress.

4. Accomplishments

Last Modified: 2/23/2016
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