The California Department of Water Resources (DWR) developed this Invasive Plant Management Plan (or Plan) as part of the Conservation Strategy of the Central Valley Flood Protection Plan (CVFPP). The Conservation Strategy tiers from the Conservation Framework, which was an integral part of the State’s preferred SSIA, identified in the 2012 CVFPP. The Conservation Strategy describes how to make progress toward meeting the environmental objectives of the Central Valley Flood Protection Act of 2008 (Act) and related legislation throughout the flood management system in the Systemwide Planning Area (SPA). The SPA comprises five Conservation Planning Areas (CPAs) in California’s Central Valley: the Feather River CPA, the Upper and Lower Sacramento River CPAs, and the Upper and Lower San Joaquin River CPAs (Figure 1-1). The SSIA includes developing and implementing multipurpose projects, and this Plan will guide the invasive plant management approaches undertaken as part of these projects.
The Conservation Strategy recognizes invasive plants as a primary stressor on the habitats, species, and ecosystem processes that are the focus of conservation planning. As of 2014, at least 68 plant species considered to be invasive by the California Invasive Plant Council (Cal-IPC) potentially occur in upland, riparian, wetland, and open water habitats in the Sacramento and San Joaquin Valleys (Cal-IPC 2013a). Many are widespread and abundant in vegetation managed as part of State Plan of Flood Control (SPFC) operation and maintenance (O&M). These species degrade riverine and floodplain habitats by altering ecosystem processes and displacing native plants. In addition, some of these invasive species, such as tamarisk (or saltcedar) (Tamarix spp.), giant reed (Arundo donax), and red sesbania (Sesbania punicea), are stressors that increase the cost and difficulty of operating and maintaining the SPFC.
These species can alter hydrology and sedimentation rates in riparian and aquatic systems (Cal-IPC 2011a) and can degrade flood system effectiveness. Importantly, recent studies have shown that certain invasive plant species have greater impacts on channel conveyance than native species adapted to the same areas (Stone et al. 2013). Dense stands of certain invasive species can alter channel morphology by retaining sediments and increasing the hydraulic roughness of the channel, which restricts flows and reduces flood conveyance (Bossard et al. 2000). For example, saltcedar traps and stabilizes alluvial sediments, narrowing stream channels and contributing to more frequent flooding (Bossard et al. 2000). Species with shallow root systems, such as giant reed and red sesbania, promote bank undercutting, collapse, and erosion (Bossard et al. 2000; Cal-IPC 2011b). Invasive terrestrial plants can reduce groundwater availability by transpiring large amounts of water, leaving less water available for native riparian vegetation (Bossard et al. 2000).
Invasive plants can also reduce the integrity of native riparian plant communities by outcompeting native plants, reducing habitat quality and food supply for wildlife, and interfering with wildlife management (Bossard et al. 2000; Cal-IPC 2011a). Nationally, invasive species are the second greatest threat to endangered species, after habitat destruction (Cal-IPC 2011a), and approximately 42 percent of the species listed as threatened or endangered by the federal Endangered Species Act (ESA) are at risk primarily because of the adverse effects of invasive species (Pimentel et al. 2005). Aquatic invasive plants can degrade aquatic habitat by reducing areas of open water used by waterfowl for resting, by shading out algae in the water column and thereby diminishing the basis of the aquatic food web, and by displacing native aquatic plants that are used for food or shelter by wildlife (Bossard et al. 2000). In addition, invasive aquatic plants often form dense mats that kill fish by lowering pH, dissolved oxygen, and light levels and by increasing carbon dioxide and turbidity (Bossard et al. 2000).
Because of these adverse effects and the threats they pose to achieving the goals of the Conservation Strategy, this Plan is driven by the following vision: to reduce the impact of invasive plants as a stressor on conservation targets and as an impediment to the operation and maintenance of the State Plan of Flood Control.
This Plan seeks to increase DWR institutional support for an SPA-wide invasive plant treatment program, and facilitate consistent invasive vegetation treatment actions by levee maintaining agencies and other partners such as the California Department of Fish and Wildlife and the United States Fish and Wildlife Service who are also conducting invasive plant control efforts. SPA-wide implementation of invasive plant treatment faces challenges that include ever-decreasing O&M budgets, regulatory requirements to protect sensitive resources, and the need to meet multiple and sometimes conflicting management objectives. This Plan recognizes those challenges, but it is beyond the scope of a single plan to resolve them all. Instead, the Plan provides first steps toward addressing the challenges through a series of goals, objectives, and implementation actions. The Plan includes measurable objectives for the treatment of four target species (Initial Priority Species) in Channel Maintenance Areas within the SPA (Channel Maintenance Areas; Figure 1-2) and identified in the DWR State Plan of Flood Control Descriptive Document (DWR 2010). It is the intent of this Plan to increase the resources available for invasive plant treatment actions by fashioning an approach that meets multiple needs and, therefore, may take advantage of funding sources not previously available for these actions.