This project summarizes the opinion of 52 experts on the future research needs in the area of invasive plants in California. Experts included academics at private and public universities, Cooperative Extension educators, land managers, members of nongovernmental organizations (NGOs), employees of restoration companies, and federal, state, and local agency personnel. Surveys were conducted through in-person interviews, written questionnaires, and workshops. The objective was to identify high-priority needs for future research on issues related to invasive plants in California's wildlands. More specifically, the goals were to (1) create a forum for assessing high-priority research needs, (2) guide future research toward these high-priority needs, and (3) facilitate connections and interactions among academic disciplines and between researchers and practitioners by increasing awareness of the range of ongoing research on invasive plants. Priority needs were chosen for 10 broad research topic areas, with specific subtopics addressed within each of these areas. In addition to noting specific research areas, there was a general need expressed for a synthesis of existing scientific information, particularly about the biology and ecology of invasive plants and the ecological impacts, control and management tools, restoration activities, and related social issues surrounding invasive plants. A mutual exchange of information was also considered important among the academic researcher and the field practitioner, as was the development of more effective training programs for land managers.

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Red sesbania is an invasive South American shrub that has rapidly expanded its range along California waterways, emphasizing the need to prioritize eradication sites at a regional scale. To accomplish this, we updated baseline location data in summer 2010 using field surveys throughout the state. We collected relevant GPS attribute data for GIS analysis and eradication prioritization modeling. The regional survey identified upstream and downstream extents for each watershed, as well as outliers in urban areas. We employed the Weed Heuristics: Invasive Population Prioritization for Eradication Tool (WHIPPET) to prioritize red sesbania sites for eradication, and revised the WHIPPET model to consider directional propagule flow of a riparian species. WHIPPET prioritized small populations isolated from larger infestations, as well as outliers in residential areas. When we compared five experts' assessments of a stratified sample of the red sesbania populations to WHIPPET's prioritization results, there was a positive, but nonsignificant, correlation. The combination of WHIPPET and independent expert opinion suggests that small, isolated populations and upstream source populations should be the primary targets for eradication. Particular attention should be paid to these small populations in watersheds where red sesbania is a new introduction. The use of this model in conjunction with evaluation by the land manager may help prevent the establishment of new seed sources and protect uninfested riparian corridors and their adjacent watersheds.

Cape ivy (Delairea odorata) is a highly invasive climbing perennial vine that is primarily distributed in coastal communities of California and Oregon, with patchy infestations in some inland riparian areas. In this study, we evaluated light as a potential environmental limitation to the spread of Cape ivy into inland regions of the western United States. Cape ivy was collected from four locations representing the north to south range. Plants were grown for 9 to 11 weeks in full sunlight and under two shade regimes (20 and 6% of full sunlight). The experiment was conducted twice at two temperature regimes. Results show some within-and among-population variability, with the southernmost San Diego County population having the highest biomass under the warmer growing conditions and the three northern populations responding most favorably in the cooler growing conditions. Despite the minor differences within and between populations, Cape ivy grew very poorly in full sunlight in both experiments. Although plants growing under 6% light grew better than those in full sunlight, they were far less robust compared to plants growing at 20% light. Our results indicate that while Cape ivy will not persist in areas with prolonged high intensity sunlight, characterized by much of the interior regions of California and Oregon, it is expected to invade and spread in areas with reduced light, including coastal regions frequently exposed to fog or cloudy conditions, or sub-canopy layers of riparian forests or woodlands. These communities should be the target areas for early detection and rapid response programs to prevent further Cape ivy invasion.